Author name code: paletou
ADS astronomy entries on 2022-09-14
author:"Paletou, Frederic" 
------------------------------------------------------------------------  

Title: The Gaia-ESO Public Spectroscopic Survey: Motivation,
    implementation, GIRAFFE data processing, analysis, and final data
    products
Authors: Gilmore, G.; Randich, S.; Worley, C. C.; Hourihane, A.;
   Gonneau, A.; Sacco, G. G.; Lewis, J. R.; Magrini, L.; Francois, P.;
   Jeffries, R. D.; Koposov, S. E.; Bragaglia, A.; Alfaro, E. J.; Allende
   Prieto, C.; Blomme, R.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.;
   Recio-Blanco, A.; Smiljanic, R.; Van Eck, S.; Zwitter, T.; Bensby, T.;
   Flaccomio, E.; Irwin, M. J.; Franciosini, E.; Morbidelli, L.; Damiani,
   F.; Bonito, R.; Friel, E. D.; Vink, J. S.; Prisinzano, L.; Abbas,
   U.; Hatzidimitriou, D.; Held, E. V.; Jordi, C.; Paunzen, E.; Spagna,
   A.; Jackson, R. J.; Maiz Apellaniz, J.; Asplund, M.; Bonifacio, P.;
   Feltzing, S.; Binney, J.; Drew, J.; Ferguson, A. M. N.; Micela, G.;
   Negueruela, I.; Prusti, T.; Rix, H. -W.; Vallenari, A.; Bergemann,
   M.; Casey, A. R.; de Laverny, P.; Frasca, A.; Hill, V.; Lind, K.;
   Sbordone, L.; Sousa, S. G.; Adibekyan, V.; Caffau, E.; Daflon, S.;
   Feuillet, D. K.; Gebran, M.; Gonzalez Hernandez, J. I.; Guiglion,
   G.; Herrero, A.; Lobel, A.; Merle, T.; Mikolaitis, S.; Montes, D.;
   Morel, T.; Ruchti, G.; Soubiran, C.; Tabernero, H. M.; Tautvaisiene,
   G.; Traven, G.; Valentini, M.; Van der Swaelmen, M.; Villanova, S.;
   Viscasillas Vazquez, C.; Bayo, A.; Biazzo, K.; Carraro, G.; Edvardsson,
   B.; Heiter, U.; Jofre, P.; Marconi, G.; Martayan, C.; Masseron, T.;
   Monaco, L.; Walton, N. A.; Zaggia, S.; Aguirre Borsen-Koch, V.; Alves,
   J.; Balaguer-Nunez, L.; Barklem, P. S.; Barrado, D.; Bellazzini, M.;
   Berlanas, S. R.; Binks, A. S.; Bressan, A.; Capuzzo-Dolcetta, R.;
   Casagrande, L.; Casamiquela, L.; Collins, R. S.; D'Orazi, V.; Dantas,
   M. L. L.; Debattista, V. P.; Delgado-Mena, E.; Di Marcantonio, P.;
   Drazdauskas, A.; Evans, N. W.; Famaey, B.; Franchini, M.; Fremat, Y.;
   Fu, X.; Geisler, D.; Gerhard, O.; Gonzalez Solares, E. A.; Grebel,
   E. K.; Gutierrez Albarran, M. L.; Jimenez-Esteban, F.; Jonsson, H.;
   Khachaturyants, T.; Kordopatis, G.; Kos, J.; Lagarde, N.; Ludwig,
   H. -G.; Mahy, L.; Mapelli, M.; Marfil, E.; Martell, S. L.; Messina,
   S.; Miglio, A.; Minchev, I.; Moitinho, A.; Montalban, J.; Monteiro,
   M. J. P. F. G.; Morossi, C.; Mowlavi, N.; Mucciarelli, A.; Murphy,
   D. N. A.; Nardetto, N.; Ortolani, S.; Paletou, F.; Palous, J.;
   Pickering, J. C.; Quirrenbach, A.; Re Fiorentin, P.; Read, J. I.;
   Romano, D.; Ryde, N.; Sanna, N.; Santos, W.; Seabroke, G. M.; Spina,
   L.; Steinmetz, M.; Stonkute, E.; Sutorius, E.; Thevenin, F.; Tosi,
   M.; Tsantaki, M.; Wright, N.; Wyse, R. F. G.; Zoccali, M.; Zorec,
   J.; Zucker, D. B.
Bibcode: 2022arXiv220805432G
Altcode:
  The Gaia-ESO Public Spectroscopic Survey is an ambitious project
  designed to obtain astrophysical parameters and elemental abundances
  for 100,000 stars, including large representative samples of the
  stellar populations in the Galaxy, and a well-defined sample of 60
  (plus 20 archive) open clusters. We provide internally consistent
  results calibrated on benchmark stars and star clusters, extending
  across a very wide range of abundances and ages. This provides a
  legacy data set of intrinsic value, and equally a large wide-ranging
  dataset that is of value for homogenisation of other and future
  stellar surveys and Gaia's astrophysical parameters. This article
  provides an overview of the survey methodology, the scientific aims,
  and the implementation, including a description of the data processing
  for the GIRAFFE spectra. A companion paper (arXiv:2206.02901)
  introduces the survey results. Gaia-ESO aspires to quantify both
  random and systematic contributions to measurement uncertainties. Thus
  all available spectroscopic analysis techniques are utilised, each
  spectrum being analysed by up to several different analysis pipelines,
  with considerable effort being made to homogenise and calibrate the
  resulting parameters. We describe here the sequence of activities up to
  delivery of processed data products to the ESO Science Archive Facility
  for open use. The Gaia-ESO Survey obtained 202,000 spectra of 115,000
  stars using 340 allocated VLT nights between December 2011 and January
  2018 from GIRAFFE and UVES. The full consistently reduced final data set
  of spectra was released through the ESO Science Archive Facility in late
  2020, with the full astrophysical parameters sets following in 2022.

Title: The Gaia-ESO Public Spectroscopic Survey: Implementation,
    data products, open cluster survey, science, and legacy
Authors: Randich, S.; Gilmore, G.; Magrini, L.; Sacco, G. G.; Jackson,
   R. J.; Jeffries, R. D.; Worley, C. C.; Hourihane, A.; Gonneau, A.;
   Viscasillas Vàzquez, C.; Franciosini, E.; Lewis, J. R.; Alfaro, E. J.;
   Allende Prieto, C.; Blomme, T. Bensby R.; Bragaglia, A.; Flaccomio, E.;
   François, P.; Irwin, M. J.; Koposov, S. E.; Korn, A. J.; Lanzafame,
   A. C.; Pancino, E.; Recio-Blanco, A.; Smiljanic, R.; Van Eck, S.;
   Zwitter, T.; Asplund, M.; Bonifacio, P.; Feltzing, S.; Binney, J.;
   Drew, J.; Ferguson, A. M. N.; Micela, G.; Negueruela, I.; Prusti,
   T.; Rix, H. -W.; Vallenari, A.; Bayo, A.; Bergemann, M.; Biazzo, K.;
   Carraro, G.; Casey, A. R.; Damiani, F.; Frasca, A.; Heiter, U.; Hill,
   V.; Jofré, P.; de Laverny, P.; Lind, K.; Marconi, G.; Martayan, C.;
   Masseron, T.; Monaco, L.; Morbidelli, L.; Prisinzano, L.; Sbordone,
   L.; Sousa, S. G.; Zaggia, S.; Adibekyan, V.; Bonito, R.; Caffau,
   E.; Daflon, S.; Feuillet, D. K.; Gebran, M.; González Hernández,
   J. I.; Guiglion, G.; Herrero, A.; Lobel, A.; Maíz Apellániz,
   J.; Merle, T.; Mikolaitis, S.; Montes, D.; Morel, T.; Soubiran,
   C.; Spina, L.; Tabernero, H. M.; Tautvaišienė, G.; Traven, G.;
   Valentini, M.; Van der Swaelmen, M.; Villanova, S.; Wright, N. J.;
   Abbas, U.; Aguirre Børsen-Koch, V.; Alves, J.; Balaguer-Núnez,
   L.; Barklem, P. S.; Barrado, D.; Berlanas, S. R.; Binks, A. S.;
   Bressan, A.; Capuzzo--Dolcetta, R.; Casagrande, L.; Casamiquela, L.;
   Collins, R. S.; D'Orazi, V.; Dantas, M. L. L.; Debattista, V. P.;
   Delgado-Mena, E.; Di Marcantonio, P.; Drazdauskas, A.; Evans, N. W.;
   Famaey, B.; Franchini, M.; Frémat, Y.; Friel, E. D.; Fu, X.; Geisler,
   D.; Gerhard, O.; González Solares, E. A.; Grebel, E. K.; Gutiérrez
   Albarrán, M. L.; Hatzidimitriou, D.; Held, E. V.; Jiménez-Esteban,
   F.; Jönsson, H.; Jordi, C.; Khachaturyants, T.; Kordopatis, G.; Kos,
   J.; Lagarde, N.; Mahy, L.; Mapelli, M.; Marfil, E.; Martell, S. L.;
   Messina, S.; Miglio, A.; Minchev, I.; Moitinho, A.; Montalban, J.;
   Monteiro, M. J. P. F. G.; Morossi, C.; Mowlavi, N.; Mucciarelli, A.;
   Murphy, D. N. A.; Nardetto, N.; Ortolani, S.; Paletou, F.; Palouus, J.;
   Paunzen, E.; Pickering, J. C.; Quirrenbach, A.; Re Fiorentin, P.; Read,
   J. I.; Romano, D.; Ryde, N.; Sanna, N.; Santos, W.; Seabroke, G. M.;
   Spagna, A.; Steinmetz, M.; Stonkuté, E.; Sutorius, E.; Thévenin,
   F.; Tosi, M.; Tsantaki, M.; Vink, J. S.; Wright, N.; Wyse, R. F. G.;
   Zoccali, M.; Zorec, J.; Zucker, D. B.; Walton, N. A.
Bibcode: 2022arXiv220602901R
Altcode:
  In the last 15 years different ground-based spectroscopic surveys
  have been started (and completed) with the general aim of delivering
  stellar parameters and elemental abundances for large samples of
  Galactic stars, complementing Gaia astrometry. Among those surveys,
  the Gaia-ESO Public Spectroscopic Survey (GES), the only one performed
  on a 8m class telescope, was designed to target 100,000 stars using
  FLAMES on the ESO VLT (both Giraffe and UVES spectrographs), covering
  all the Milky Way populations, with a special focus on open star
  clusters. This article provides an overview of the survey implementation
  (observations, data quality, analysis and its success, data products,
  and releases), of the open cluster survey, of the science results and
  potential, and of the survey legacy. A companion article (Gilmore et
  al.) reviews the overall survey motivation, strategy, Giraffe pipeline
  data reduction, organisation, and workflow. The GES has determined
  homogeneous good-quality radial velocities and stellar parameters for a
  large fraction of its more than 110,000 unique target stars. Elemental
  abundances were derived for up to 31 elements for targets observed with
  UVES. Lithium abundances are delivered for about 1/3 of the sample. The
  analysis and homogenisation strategies have proven to be successful;
  several science topics have been addressed by the Gaia-ESO consortium
  and the community, with many highlight results achieved. The final
  catalogue has been released through the ESO archive at the end of
  May 2022, including the complete set of advanced data products. In
  addition to these results, the Gaia-ESO Survey will leave a very
  important legacy, for several aspects and for many years to come.

Title: Deep learning application for stellar parameters determination:
    I-constraining the hyperparameters
Authors: Gebran, Marwan; Connick, Kathleen; Farhat, Hikmat; Paletou,
   Frédéric; Bentley, Ian
Bibcode: 2022OAst...31...38G
Altcode: 2022arXiv220112476G
  Machine learning is an efficient method for analysing and interpreting
  the increasing amount of astronomical data that are available. In
  this study, we show a pedagogical approach that should benefit anyone
  willing to experiment with deep learning techniques in the context
  of stellar parameter determination. Using the convolutional neural
  network architecture, we give a step-by-step overview of how to
  select the optimal parameters for deriving the most accurate values
  for the stellar parameters of stars: T<SUB>eff</SUB>, log g, [M/H],
  and v<SUB>e</SUB>sin i. Synthetic spectra with random noise were used
  to constrain this method and to mimic the observations. We found that
  each stellar parameter requires a different combination of network
  hyperparameters and the maximum accuracy reached depends on this
  combination as well as the signal-to-noise ratio of the observations,
  and the architecture of the network. We also show that this technique
  can be applied to other spectral-types in different wavelength ranges
  after the technique has been optimized.

Title: The use of Deep Learning in stellar classification
Authors: Connick, Kathleen; Gebran, Marwan; Paletou, Frédéric
Bibcode: 2021scgr.confE...1C
Altcode:
  We are applying various ML/DL techniques for the purpose of stellar
  spectroscopy. Having already ran tests with Principal Component Analysis
  (PCA) and Sliced Inverse Regression (SIR), we now turn our focus to
  Convolution Neural Network (CNN), among other techniques, in order to
  find the most accurate derivations for stellar parameters: effective
  temperature, surface gravity, projected equatorial rotational velocity,
  microturbulence velocity and metallicity.

Title: VizieR Online Data Catalog: ESPaDOnS and NARVAL
    spectropolarimeters (IRAP) (Petit P., 2021)
Authors: Petit, P.; Paletou, F.; Mathias, P.; Glorian, Jm.; Amato, A.
Bibcode: 2021yCat....102043P
Altcode:
  We list the stellar spectroscopic and spectropolarimetric observations
  available in the PolarBase data base. For each star equatorial
  coordinates, first Julian date of observation, last Julian date
  of observation, number of observations are given, and a detection
  diagnosis of polarized signatures (in cross-correlated pseudo-line
  profiles) are given. <P />(1 data file).

Title: Full non-LTE spectral line formation. I. Setting the stage
Authors: Paletou, F.; Peymirat, C.
Bibcode: 2021A&A...649A.165P
Altcode: 2021arXiv210312009P
  Radiative transfer out of local thermodynamic equilibrium (NLTE) has
  been increasingly adressed, mostly numerically, for about six decades
  now. However, the standard NLTE problem most often refers to the
  only deviation of the distribution of photons from their equilibrium,
  that is to say a Planckian distribution. Hereafter we revisit after
  Oxenius (1986, Kinetic theory of particles and Photons - Theoretical
  Foundations of non-LTE Plasma Spectroscopy, Springer) the so-called
  full NLTE problem, which considers coupling and therefore solving
  self-consistently for deviations from equilibrium distributions of
  photons as well as for massive particles constituting the atmospheric
  plasma.

Title: An adaptive Gaussian quadrature for the Voigt function
Authors: Paletou, F.; Peymirat, C.; Anterrieu, E.; Böhm, T.
Bibcode: 2020A&A...633A.111P
Altcode: 2019arXiv191208427P
  We evaluate an adaptive Gaussian quadrature integration scheme
  suitable for the numerical evaluation of generalized redistribution
  in frequency functions. The latter are indispensable ingredients for
  "full non-LTE" radiation transfer computations, assuming potential
  deviations of the velocity distribution of massive particles from the
  usual Maxwell-Boltzmann distribution. A first validation is made with
  computations of the usual Voigt profile.

Title: VizieR Online Data Catalog: Stellar parameters of M and K
    dwarfs (Houdebine+, 2019)
Authors: Houdebine, E. R.; Mullan, D. J.; Doyle, J. G.; de La
   Vieuville, G.; Butler, C. J.; Paletou, F.
Bibcode: 2019yCat..51580056H
Altcode:
  Observations of (R-I)<SUB>C</SUB> (Cousin's photometric system) or
  (R-I)&lt;SU photometric system) for our samples of K and M dwarfs
  were taken from several papers. We selected eight samples of K and M
  dwarfs according to their (R-I)<SUB>C</SUB> colors. This represents
  a total sample of 2765 K and M dwarfs. Most stars in this sample
  are nearby or large proper motion stars. We also completed these
  samples of stars with a ninth sample of stars: the M0-M1 sample,
  which includes some stars from the samples of stars from B12 and M15
  (see Table 1), as well as several stars initially from the M2 sample,
  which were found to have higher temperatures (we included in the M0-M1
  sample stars down to the spectral type dM1.5). <P />(3 data files).

Title: The Mass-Activity Relationships in M and K Dwarfs. I. Stellar
    Parameters of Our Sample of M and K Dwarfs
Authors: Houdebine, Éric R.; Mullan, D. J.; Doyle, J. G.; de La
   Vieuville, Geoffroy; Butler, C. J.; Paletou, F.
Bibcode: 2019AJ....158...56H
Altcode: 2019arXiv190507921H
  Empirical correlations between stellar parameters such as rotation
  or radius and magnetic activity diagnostics require estimates
  of the effective temperatures and the stellar radii. The aim of
  this study is to propose simple methods that can be applied to
  large samples of stars in order to derive estimates of the stellar
  parameters. Good empirical correlations between red/infrared colors
  (e.g., (R - I)<SUB> C </SUB>) and effective temperatures have been
  well established for a long time. The more recent (R - I)<SUB> C
  </SUB> color-T <SUB>eff</SUB> correlation using the data of Mann et
  al. (hereafter M15) and Boyajian et al. (hereafter B12) shows that
  this color can be applied as a temperature estimate for large samples
  of stars. We find that the mean scatter in T <SUB>eff</SUB> relative
  to the (R - I)<SUB> C </SUB>-T <SUB>eff</SUB> relationship of B12 and
  M15 data is only ±3σ = 44.6 K for K dwarfs and ±3σ = 39.4 K for M
  dwarfs. These figures are small and show that the (R - I)<SUB> C </SUB>
  color can be used as a first-guess effective temperature estimator
  for K and M dwarfs. We derive effective temperatures for about 1910
  K and M dwarfs using the calibration of (R - I)<SUB> C </SUB> color-T
  <SUB>eff</SUB> from B12 and M15 data. We also compiled T <SUB>eff</SUB>
  and metallicity measurements available in the literature using the
  VizieR database. We determine T <SUB>eff</SUB> for 441 stars with
  previously unknown effective temperatures. We also identified 21 new
  spectroscopic binaries and one triple system from our high-resolution
  spectra. <P />Based on Gaia DR2 and Hipparcos parallax measurements.

Title: Sliced Inverse Regression: application to fundamental stellar
    parameters
Authors: Kassounian, Sarkis; Gebran, Marwan; Paletou, Frédéric;
   Watson, Victor
Bibcode: 2019OAst...28...68K
Altcode: 2019arXiv190111003K
  We present a method for deriving the stellar fundamental parameters. It
  is based on a regularized sliced inverse regression (RSIR).We first
  tested it on noisy synthetic spectra of A, F, G, and K-type stars,
  and inverted simultaneously their atmospheric fundamental parameters:
  T<SUB>eff</SUB>., log g, [M/H] and v sin i. Different learning databases
  were calculated using a range of sampling in T<SUB>eff</SUB>., log g,
  v sin i, and [M/H]. Combined with a principal component analysis
  (PCA) nearest neighbors (NN) search, the size of the learning
  database is reduced. A Tikhonov regularization is applied, given the
  ill-conditioning of SIR. For all spectral types, decreasing the size of
  the learning database allowed us to reach internal accuracies better
  than PCA-based NN-search using larger learning databases. For each
  analyzed parameter, we have reached internal errors that are smaller
  than the sampling step of the parameter. We have also applied the
  technique to a sample of observed FGK and A stars. For a selection
  of well-studied stars, the inverted parameters are in agreement with
  the ones derived in previous studies. The RSIR inversion technique,
  complemented with PCA pre-processing proves to be efficient in
  estimating stellar parameters of A, F, G, and K-type stars.

Title: Toulouse 2D numerical radiative transfer codes
Authors: Paletou, F.; Léger, L.; Chane-Yook, M.; Auer, L. H.
Bibcode: 2019arXiv190305971P
Altcode:
  A tutorial associated with the distribution of 2D non-LTE multilevel
  atom radiative transfer codes.

Title: Deep learning determination of stellar atmospheric fundamental
    parameters
Authors: Kou, R.; Petit, P.; Paletou, F.; Kulenthirarajah, L.; Glorian,
   J. -M.
Bibcode: 2018sf2a.conf..167K
Altcode:
  In order to estimate fundamental parameters (effective temperature,
  surface gravity and metallicity) of the large amount of stars in the
  PolarBase data base, we need a fast and reliable algorithm. With this
  aim, we developed a convolutional neural network able to derive this
  parameter triplet. Our neural network was trained on observed spectra
  from the PolarBase and Elodie data bases (M to F stars). We used the
  spectral region between 6095 and 6185 Angströms which has proved its
  efficiency in a number of previous studies. We analyzed the outcome
  of our approach for a sample of spectra from the same data bases. We
  discuss the accuracy and reliability of the neural network depending
  on the parameter domain, size and quality of the training data set.

Title: On Milne-Barbier-Unsöld relationships
Authors: Paletou, Frédéric
Bibcode: 2018OAst...27...76P
Altcode: 2017arXiv171107026P
  This short review aims to clarify upon the origins of so-called
  Eddington-Barbier relationships, which relate the emergent specific
  intensity and the flux to the photospheric source function at specific
  optical depths. Here we discuss the assumptions behind the original
  derivation of Barbier (1943).We also point to the fact that Milne had
  already formulated these two relations in 1921.

Title: VizieR Online Data Catalog: Rotation-Activity Correlations
    in K-M dwarfs. I. (Houdebine+, 2016)
Authors: Houdebine, E. R.; Mullan, D. J.; Paletou, F.; Gebran, M.
Bibcode: 2017yCat..18220097H
Altcode:
  We selected a sample of 419 late-K dwarfs on the basis of (R-I)
  measurements available in the literature. Searching through databases
  at the European Southern Observatory (ESO) and Observatoire de Haute
  Provence (OHP), we identified spectra of 112 different stars that
  are suitable for our purposes. The spectra that we use to determine
  vsini came from two different echelle spectrographs: HARPS (High
  Accuracy Radial velocity Planet Search, ESO; R=115000) and SOPHIE
  (OHP; R=75000). <P />(6 data files).

Title: VizieR Online Data Catalog: Rotation-Activity Correlations
    in K-M dwarfs II. (Houdebine+, 2017)
Authors: Houdebine, E. R.; Mullan, D. J.; Bercu, B.; Paletou, F.;
   Gebran, M.
Bibcode: 2017yCat..18370096H
Altcode:
  The spectra that we use for determining the CaII and Hα equivalent
  widths in the present study of dK4-dM4 stars came from three different
  echelle spectrographs; HARPS (High Accuracy Radial velocity Planet
  Search, ESO), SOPHIE (OHP), and FEROS (The Fiber-fed Extended Range
  Optical Spectrograph). <P />The stars in our samples include all stars
  from all observing programs that have been carried out with HARPS
  and SOPHIE for stars belonging to the following spectral sub-types:
  dK4, dK6, dM2, and dM3. For dM4 stars, we compiled all measurements
  of vsini available in the literature (see Paper I; Houdebine+ 2016,
  J/ApJ/822/97). For the dK6 and dM3 samples, we also supplemented
  our own measurements with measurements available in the literature,
  notably for active stars (see Paper I). <P />(7 data files).

Title: Inference of an explanatory variable from observations in
a high-dimensional space: application to high-resolution spectra
    of stars
Authors: Watson, V.; Trouilhet, JF.; Paletou, F.; Girard, S.
Bibcode: 2017arXiv170602213W
Altcode:
  Our aim is to evaluate fundamental parameters from the analysis of the
  electromagnetic spectra of stars. We may use $10^3$-$10^5$ spectra;
  each spectrum being a vector with $10^2$-$10^4$ coordinates. We thus
  face the so-called "curse of dimensionality". We look for a method
  to reduce the size of this data-space, keeping only the most relevant
  information.As a reference method, we use principal component analysis
  (PCA) to reduce dimensionality. However, PCA is an unsupervised method,
  therefore its subspace was not consistent with the parameter. We thus
  tested a supervised method based on Sliced Inverse Regression (SIR),
  which provides a subspace consistent with the parameter. It also shares
  analogies with factorial discriminant analysis: the method slices the
  database along the parameter variation, and builds the subspace which
  maximizes the inter-slice variance, while standardizing the total
  projected variance of the data. Nevertheless the performances of SIR
  were not satisfying in standard usage, because of the non-monotonicity
  of the unknown function linking the data to the parameter and because
  of the noise propagation. We show that better performances can be
  achieved by selecting the most relevant directions for parameter
  inference. Preliminary tests are performed on synthetic pseudo-line
  profiles plus noise. Using one direction, we show that compared to
  PCA, the error associated with SIR is 50$\%$ smaller on a non-linear
  parameter, and 70$\%$ smaler on a linear parameter. Moreover, using
  a selected direction, the error is 80$\%$ smaller for a non-linear
  parameter, and 95$\%$ smaller for a linear parameter.

Title: Sliced Inverse Regression for the inference of stellar
    fundamental parameters
Authors: Watson, V.; Trouilhet, JF.; Paletou, F.; Gebran, M.
Bibcode: 2017arXiv170610121W
Altcode:
  We aim at finding the value of an explanatory variable, through its
  expression in a large data-vector, without knowing the link function
  between the explanatory variable and the data-space. Sliced Inverse
  Regression (SIR) method allows for the projection of a data-vector onto
  a subspace consistent with the explanatory variable variation. We
  suggest a method based on the SIR subspace, that gives the most
  efficient estimation of an unknown explanatory variable.

Title: The Rotation-Activity Correlations in K and M Dwarfs. II. New
    Constraints on the Dynamo Mechanisms in Late-K and M Dwarfs Before
    and At the Transition to Complete Convection
Authors: Houdebine, E. R.; Mullan, D. J.; Bercu, B.; Paletou, F.;
   Gebran, M.
Bibcode: 2017ApJ...837...96H
Altcode: 2017arXiv170107608H
  We study the rotation-activity correlations (RACs) in a sample of
  stars from spectral type dK4 to dM4. We study RACs using chromospheric
  data and coronal data. We study the Ca II line surface fluxes-P/\sin
  I RACs. We fit the RACs with linear homoscedastic and heteroscedastic
  regression models. We find that these RACs differ substantially from
  one spectral sub-type to another. For dM3 and dM4 stars, we find
  that the RACs cannot be described by a simple model, but instead
  that there may exist two distinct RAC behaviors for the low-activity
  and the high-activity stellar sub-samples, respectively. Although
  these results are preliminary and will need confirmation, the data
  suggest that these distinct RACs may be associated with different
  dynamo regimes. We also study {R}<SUB>{HK</SUB>}<SUP>\prime </SUP>
  as a function of the Rossby number R <SUB>0</SUB>. We find (I) for
  dK4 stars, {R}<SUB>{HK</SUB>}<SUP>\prime </SUP> as a function of R
  <SUB>0</SUB> agrees well with previous results for F-G-K stars and
  (II) in dK6, dM2, dM3, and dM4 stars, at a given R <SUB>0</SUB>, the
  values of {R}<SUB>{HK</SUB>}<SUP>\prime </SUP> lie at a factor of 3,
  10, 20, and 90, respectively, below the F-G-K RAC. Our results suggest
  a significant decrease in the efficiency of the dynamo mechanism(s)
  as regards chromospheric heating before and at dM3, I.e., before and at
  the transition to complete convection. We also show that the ratio of
  coronal heating to chromospheric heating L <SUB>X</SUB>/L <SUB>HK</SUB>
  increases by a factor of 100 between dK4 and dM4 stars. <P />Based
  on observations available at Observatoire de Haute Provence and the
  European Southern Observatory databases and on Hipparcos parallax
  measurements.

Title: Discovery of a complex linearly polarized spectrum of
    Betelgeuse dominated by depolarization of the continuum
Authors: Aurière, M.; López Ariste, A.; Mathias, P.; Lèbre, A.;
   Josselin, E.; Montargès, M.; Petit, P.; Chiavassa, A.; Paletou, F.;
   Fabas, N.; Konstantinova-Antova, R.; Donati, J. -F.; Grunhut, J. H.;
   Wade, G. A.; Herpin, F.; Kervella, P.; Perrin, G.; Tessore, B.
Bibcode: 2016A&A...591A.119A
Altcode: 2016arXiv160504702A
  Context. <ASTROBJ>Betelgeuse</ASTROBJ> is an M supergiant that
  harbors spots and giant granules at its surface and presents linear
  polarization of its continuum. <BR /> Aims: We have previously
  discovered linear polarization signatures associated with
  individual lines in the spectra of cool and evolved stars. Here,
  we investigate whether a similar linearly polarized spectrum exists
  for <ASTROBJ>Betelgeuse</ASTROBJ>. <BR /> Methods: We used the
  spectropolarimeter Narval, combining multiple polarimetric sequences
  to obtain high signal-to-noise ratio spectra of individual lines, as
  well as the least-squares deconvolution (LSD) approach, to investigate
  the presence of an averaged linearly polarized profile for the
  photospheric lines. <BR /> Results: We have discovered the existence
  of a linearly polarized spectrum for <ASTROBJ>Betelgeuse</ASTROBJ>,
  detecting a rather strong signal (at a few times 10<SUP>-4</SUP>
  of the continuum intensity level), both in individual lines and in
  the LSD profiles. Studying its properties and the signal observed for
  the resonant Na I D lines, we conclude that we are mainly observing
  depolarization of the continuum by the absorption lines. The linear
  polarization of the Betelgeuse continuum is due to the anisotropy of
  the radiation field induced by brightness spots at the surface and
  Rayleigh scattering in the atmosphere. We have developed a geometrical
  model to interpret the observed polarization, from which we infer the
  presence of two brightness spots and their positions on the surface
  of <ASTROBJ>Betelgeuse</ASTROBJ>. We show that applying the model
  to each velocity bin along the Stokes Q and U profiles allows the
  derivation of a map of the bright spots. We use the Narval linear
  polarization observations of <ASTROBJ>Betelgeuse</ASTROBJ> obtained
  over a period of 1.4 yr to study the evolution of the spots and of the
  atmosphere. <BR /> Conclusions: Our study of the linearly polarized
  spectrum of <ASTROBJ>Betelgeuse</ASTROBJ> provides a novel method
  for studying the evolution of brightness spots at its surface and
  complements quasi-simultaneous observations obtained with PIONIER at
  the VLTI. <P />Based on observations obtained at the Télescope Bernard
  Lyot (TBL) at Observatoire du Pic du Midi, CNRS/INSU and Université
  de Toulouse, France.

Title: A new method for the inversion of atmospheric parameters of
    A/Am stars
Authors: Gebran, M.; Farah, W.; Paletou, F.; Monier, R.; Watson, V.
Bibcode: 2016A&A...589A..83G
Altcode: 2016arXiv160301146G
  Context. We present an automated procedure that simultaneously derives
  the effective temperature T<SUB>eff</SUB>, surface gravity log g,
  metallicity [Fe/H], and equatorial projected rotational velocity vsini
  for "normal" A and Am stars. The procedure is based on the principal
  component analysis (PCA) inversion method, which we published in a
  recent paper . <BR /> Aims: A sample of 322 high-resolution spectra
  of F0-B9 stars, retrieved from the Polarbase, SOPHIE, and ELODIE
  databases, were used to test this technique with real data. We selected
  the spectral region from 4400-5000 Å as it contains many metallic
  lines and the Balmer Hβ line. <BR /> Methods: Using three data sets
  at resolving powers of R = 42 000, 65 000 and 76 000, about ~6.6 ×
  10<SUP>6</SUP> synthetic spectra were calculated to build a large
  learning database. The online power iteration algorithm was applied to
  these learning data sets to estimate the principal components (PC). The
  projection of spectra onto the few PCs offered an efficient comparison
  metric in a low-dimensional space. The spectra of the well-known A0-
  and A1-type stars, Vega and Sirius A, were used as control spectra
  in the three databases. Spectra of other well-known A-type stars
  were also employed to characterize the accuracy of the inversion
  technique. <BR /> Results: We inverted all of the observational
  spectra and derived the atmospheric parameters. After removal of a
  few outliers, the PCA-inversion method appeared to be very efficient
  in determining T<SUB>eff</SUB>, [Fe/H], and vsini for A/Am stars. The
  derived parameters agree very well with previous determinations. Using
  a statistical approach, deviations of around 150 K, 0.35 dex, 0.15 dex,
  and 2 km s<SUP>-1</SUP> were found for T<SUB>eff</SUB>, log g, [Fe/H],
  and vsini with respect to literature values for A-type stars. <BR />
  Conclusions: The PCA inversion proves to be a very fast, practical,
  and reliable tool for estimating stellar parameters of FGK and
  A stars and for deriving effective temperatures of M stars. <P
  />Based on data retrieved from the Polarbase, SOPHIE, and ELODIE
  archives.Table 2 is only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A83">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A83</A>

Title: Rotation-Activity Correlations in K and M Dwarfs. I. Stellar
    Parameters and Compilations of v sin I and P/sin I for a Large Sample
    of Late-K and M Dwarfs
Authors: Houdebine, E. R.; Mullan, D. J.; Paletou, F.; Gebran, M.
Bibcode: 2016ApJ...822...97H
Altcode: 2016arXiv160407920H
  The reliable determination of rotation-activity correlations (RACs)
  depends on precise measurements of the following stellar parameters:
  T <SUB>eff</SUB>, parallax, radius, metallicity, and rotational speed
  v sin I. In this paper, our goal is to focus on the determination of
  these parameters for a sample of K and M dwarfs. In a future paper
  (Paper II), we will combine our rotational data with activity data
  in order to construct RACs. Here, we report on a determination of
  effective temperatures based on the (R-I)<SUB> C </SUB> color from
  the calibrations of Mann et al. and Kenyon &amp; Hartmann for four
  samples of late-K, dM2, dM3, and dM4 stars. We also determine stellar
  parameters (T <SUB>eff</SUB>, log(g), and [M/H]) using the principal
  component analysis-based inversion technique for a sample of 105 late-K
  dwarfs. We compile all effective temperatures from the literature for
  this sample. We determine empirical radius-[M/H] correlations in our
  stellar samples. This allows us to propose new effective temperatures,
  stellar radii, and metallicities for a large sample of 612 late-K and
  M dwarfs. Our mean radii agree well with those of Boyajian et al. We
  analyze HARPS and SOPHIE spectra of 105 late-K dwarfs, and we have
  detected v sin I in 92 stars. In combination with our previous v sin
  I measurements in M and K dwarfs, we now derive P/sin I measures for
  a sample of 418 K and M dwarfs. We investigate the distributions of
  P/sin I, and we show that they are different from one spectral subtype
  to another at a 99.9% confidence level. <P />Based on observations
  available at Observatoire de Haute Provence and the European Southern
  Observatory databases and on Hipparcos parallax measurements.

Title: VizieR Online Data Catalog: PCA-based inversion of stellar
    parameters (Gebran+, 2016)
Authors: Gebran, M.; Farah, W.; Paletou, F.; Monier, R.; Watson, V.
Bibcode: 2016yCat..35890083G
Altcode:
  Inverted effective temperatures, surface gravities, projected rotational
  velocities, metalicities, and radial velocities for the selected
  A stars. The "closest" are the values found in Vizier catalogues
  closest to our inverted parameters, while "median" are the median of
  the catalogue values. Outliers are marked as "1" in the "outliers"
  column (see sect. 6) <P />(1 data file).

Title: Numerical radiative transfer with state-of-the-art iterative
    methods made easy
Authors: Lambert, Julien; Paletou, Frédéric; Josselin, Eric;
   Glorian, Jean-Michel
Bibcode: 2016EJPh...37a5603L
Altcode: 2015arXiv150901158L
  This article presents an on-line tool and its accompanying software
  resources for the numerical solution of basic radiation transfer out
  of local thermodynamic equilibrium (LTE). State-of-the-art stationary
  iterative methods such as Accelerated Λ-iteration and Gauss-Seidel
  schemes, using a short characteristics-based formal solver are
  used. We also comment on typical numerical experiments associated to
  the basic non-LTE radiation problem. These resources are intended for
  the largest use and benefit, in support to more classical radiation
  transfer lectures usually given at the Master level.

Title: Estimating Stellar Fundamental Parameters Using PCA:
    Application to Early Type Stars of GES Data
Authors: Farah, W.; Gebran, M.; Paletou, F.; Blomme, R.
Bibcode: 2015sf2a.conf....3F
Altcode: 2015arXiv150803978F
  This work addresses a procedure to estimate fundamental stellar
  parameters such as T_{eff}, log g, [Fe/H], and v sin i using a
  dimensionality reduction technique called principal component analysis
  (PCA), applied to a large database of synthetic spectra. This technique
  shows promising results for inverting stellar parameters of observed
  targets from Gaia Eso Survey.

Title: The GSO Data Centre
Authors: Paletou, F.; Glorian, J. -M.; Génot, V.; Rouillard, A.;
   Petit, P.; Palacios, A.; Caux, E.; Wakelam, V.
Bibcode: 2015sf2a.conf...37P
Altcode: 2015arXiv150803163P
  Hereafter we describe the activities of the Grand Sud-Ouest Data
  Centre operated for INSU (CNRS) by the OMP--IRAP and the Université
  Paul Sabatier in Toulouse, in a collaboration with the OASU--LAB in
  Bordeaux and OREME--LUPM in Montpellier.

Title: Principal component analysis-based inversion of effective
    temperatures for late-type stars
Authors: Paletou, F.; Gebran, M.; Houdebine, E. R.; Watson, V.
Bibcode: 2015A&A...580A..78P
Altcode: 2015arXiv150704202P
  We show how the range of application of the principal component
  analysis-based inversion method of Paletou et al. (2015, A&amp;A,
  573, A67) can be extended to data for late-type stars. Besides being
  an extension of its original application domain, which applied to FGK
  stars, we also used synthetic spectra for our learning database. We
  discuss our results for effective temperatures in comparison with
  previous evaluations made available from VizieR and Simbad services at
  CDS. <P />Based on data obtained from the ESO Science Archive Facility.

Title: Discovery of starspots on Vega. First spectroscopic detection
    of surface structures on a normal A-type star
Authors: Böhm, T.; Holschneider, M.; Lignières, F.; Petit, P.;
   Rainer, M.; Paletou, F.; Wade, G.; Alecian, E.; Carfantan, H.;
   Blazère, A.; Mirouh, G. M.
Bibcode: 2015A&A...577A..64B
Altcode: 2014arXiv1411.7789B
  Context. The theoretically studied impact of rapid rotation on stellar
  evolution needs to be compared with these results of high-resolution
  spectroscopy-velocimetry observations. Early-type stars present a
  perfect laboratory for these studies. The prototype A0 star Vega has
  been extensively monitored in recent years in spectropolarimetry. A
  weak surface magnetic field was detected, implying that there might
  be a (still undetected) structured surface. First indications of the
  presence of small amplitude stellar radial velocity variations have
  been reported recently, but the confirmation and in-depth study with
  the highly stabilized spectrograph SOPHIE/OHP was required. <BR />
  Aims: The goal of this article is to present a thorough analysis of
  the line profile variations and associated estimators in the early-type
  standard star Vega (A0) in order to reveal potential activity tracers,
  exoplanet companions, and stellar oscillations. <BR /> Methods: Vega
  was monitored in quasi-continuous high-resolution echelle spectroscopy
  with the highly stabilized velocimeter SOPHIE/OHP. A total of 2588
  high signal-to-noise spectra was obtained during 34.7 h on five
  nights (2 to 6 of August 2012) in high-resolution mode at R = 75 000
  and covering the visible domain from 3895-6270 Å. For each reduced
  spectrum, least square deconvolved equivalent photospheric profiles were
  calculated with a T<SUB>eff</SUB> = 9500 and log g = 4.0 spectral line
  mask. Several methods were applied to study the dynamic behaviour of
  the profile variations (evolution of radial velocity, bisectors, vspan,
  2D profiles, amongst others). <BR /> Results: We present the discovery
  of a spotted stellar surface on an A-type standard star (Vega) with
  very faint spot amplitudes ΔF/Fc ~ 5 × 10<SUP>-4</SUP>. A rotational
  modulation of spectral lines with a period of rotation P = 0.68 d has
  clearly been exhibited, unambiguously confirming the results of previous
  spectropolarimetric studies. Most of these brightness inhomogeneities
  seem to be located in lower equatorial latitudes. Either a very thin
  convective layer can be responsible for magnetic field generation at
  small amplitudes, or a new mechanism has to be invoked to explain the
  existence of activity tracing starspots. At this stage it is difficult
  to disentangle a rotational from a stellar pulsational origin for the
  existing higher frequency periodic variations. <BR /> Conclusions:
  This first strong evidence that standard A-type stars can show surface
  structures opens a new field of research and ask about a potential
  link with the recently discovered weak magnetic field discoveries in
  this category of stars. <P />Based on observations obtained with the
  SOPHIE spectrograph at the 2 m OHP telescope operated by the Institut
  National des Sciences de l'Univers (INSU) of the Centre National de
  la Recherche Scientifique of France (CNRS).

Title: VizieR Online Data Catalog: Fundamental stellar parameters
    from PolarBase (Paletou+, 2015)
Authors: Paletou, F.; Boehm, T.; Watson, V.; Trouilhet, J. -F.
Bibcode: 2015yCat..35730067P
Altcode: 2015yCat..35739067P
  Our reference spectra are taken from the Elodie stellar library
  (Prugniel et al. 2007, astro-ph/0703658, Cat. III/251; Prugniel
  &amp; Soubiran 2001A&amp;A...369.1048P, Cat. III/218). <P />Our
  main purpose is inverting of stellar parameters from high-resolution
  spectra coming from Narval and ESPaDOnS spectropolarimeters. These
  data are now available from the public database PolarBase (Petit et
  al., 2014PASP..126..469P, Cat. J/PASP/126/469). Narval is a modern
  spectropolarimeter operating in the 380-1000nm spectral domain,
  with a spectral resolution of 65000 in its polarimetric mode. It is
  an improved copy, adapted to the 2m TBL telescope, of the ESPaDOnS
  spectropolarimeter, which is in operations since 2004 at the 3.6m
  aperture CFHT telescope. <P />(1 data file).

Title: Inversion of stellar fundamental parameters from ESPaDOnS
    and Narval high-resolution spectra
Authors: Paletou, F.; Böhm, T.; Watson, V.; Trouilhet, J. -F.
Bibcode: 2015A&A...573A..67P
Altcode: 2014arXiv1411.4859P
  The general context of this study is the inversion of stellar
  fundamental parameters from high-resolution Echelle spectra. We aim at
  developing a fast and reliable tool for the post-processing of spectra
  produced by ESPaDOnS and Narval spectropolarimeters. Our inversion
  tool relies on principal component analysis. It allows reducing
  dimensionality and defining a specific metric for the search of
  nearest neighbours between an observed spectrum and a set of observed
  spectra taken from the Elodie stellar library. Effective temperature,
  surface gravity, total metallicity, and projected rotational velocity
  are derived. Various tests presented in this study that were based
  solely on information coming from a spectral band centred on the Mg i
  b-triplet and had spectra from FGK stars are very promising. <P />Based
  on observations obtained at the Télescope Bernard Lyot (TBL, Pic du
  Midi, France), which is operated by the Observatoire Midi-Pyrénées,
  Université de Toulouse, Centre National de la Recherche Scientifique
  (France) and the Canada-France-Hawaii Telescope (CFHT) which is operated
  by the National Research Council of Canada, CNRS/INSU and the University
  of Hawaii (USA).

Title: Using Virtual Observatory with Python: querying remote
    astronomical databases
Authors: Paletou, F.; Zolotukhin, I.
Bibcode: 2014arXiv1408.7026P
Altcode:
  This tutorial is devoted to extending an existing catalogue with
  data taken elsewhere, either from CDS Vizier or Simbad database. As
  an example, we used the so-called 'Spectroscopic Survey of Stars
  in the Solar Neighborhood' (aka. S4N, Allende Prieto et al. 2004)
  in order to retrieve all objects with available data for the set of
  fundamental stellar parameters effective temperature, surface gravity
  and metallicity. Then for each object in this dataset we query Simbad
  database to retrieve the projected rotational velocity. This combines
  Vizier and Simbad queries made using Python astroquery module. The
  tutorial covers remote database access, filtering tables with arbitrary
  criteria, creating and writing your own tables, and basics of plotting
  in Python.

Title: VizieR Online Data Catalog: PolarBase catalogue of stellar
    spectra (Petit+, 2014)
Authors: Petit, P.; Louge, T.; Theado, S.; Paletou, F.; Manset, N.;
   Morin, J.; Marsden, S. C.; Jeffers, S. V.
Bibcode: 2014yCat..61260469P
Altcode:
  We list the stellar spectroscopic and spectropolarimetric observations
  available in the PolarBase data base. For each star equatorial
  coordinates, first Julian date of observation, last Julian date
  of observation, number of observations are given, and a detection
  diagnosis of polarized signatures (in cross-correlated pseudo-line
  profiles) are given. <P />(1 data file).

Title: PolarBase: A Database of High-Resolution Spectropolarimetric
    Stellar Observations
Authors: Petit, P.; Louge, T.; Théado, S.; Paletou, F.; Manset, N.;
   Morin, J.; Marsden, S. C.; Jeffers, S. V.
Bibcode: 2014PASP..126..469P
Altcode: 2014arXiv1401.1082P
  PolarBase is an evolving data base that contains all stellar
  data collected with the ESPaDOnS and NARVAL high-resolution
  spectropolarimeters, in their reduced form, as soon as they become
  public. As of early 2014, observations of 2,000 stellar objects
  throughout the Hertzsprung-Russell diagram are available. Intensity
  spectra are available for all targets, and the majority of the
  observations also include simultaneous spectra in circular or linear
  polarization, with the majority of the polarimetric measurements being
  performed only in circularly polarized light (Stokes V). Observations
  are associated with a cross-correlation pseudo-line profile in all
  available Stokes parameters, greatly increasing the detectability
  of weak polarized signatures. Stokes V signatures are detected
  for more than 300 stars of all masses and evolutionary stages, and
  linear polarization is detected in 35 targets. The detection rate in
  Stokes V is found to be anti-correlated with the stellar effective
  temperature. This unique set of Zeeman detections offers the first
  opportunity to run homogeneous magnetometry studies throughout
  the H-R diagram. The web interface of PolarBase is available at
  http://polarbase.irap.omp.eu.

Title: PCA-based inversion of stellar fundamental parameters from
    high-resolution Echelle spectra
Authors: Paletou, F.; Trouilhet, J. -F.; Boehm, T.
Bibcode: 2014arXiv1401.1083P
Altcode:
  The general context of this study is the inversion of stellar
  fundamental parameters from high-resolution Echelle spectra. We
  aim at developing a fast and reliable tool for the post-processing
  of spectra produced, in particular, by the Espadons and Narval
  spectropolarimeters. Our inversion tool relies on principal component
  analysis. It allows reduction of dimensionality and the definition
  of a specific metric for the search of nearest neighbours between an
  observed spectrum and a set of synthetic spectra. Effective temperature,
  surface gravity, total metallicity and projected rotation velocity are
  derived. Our first tests, essentially done from the sole information
  coming from the spectral band that the RVS spectrometer will soon
  observe from the GAIA space observatory, and with spectra from mainly
  FGK-dwarfs are very promising. We also tested our method with a few
  targets beyond this domain of the H-R diagram.

Title: Conceptual design of the data handling system for the European
    Solar Telescope
Authors: Ermolli, Ilaria; Cauzzi, Gianna; Collados, Manuel; Paletou,
   Frederic; Reardon, Kevin; Aboudarham, Jean; Cirami, Roberto; Cosentino,
   Rosario; Del Moro, Dario; Di Marcantonio, Paolo; Giorgi, Fabrizio;
   Lafon, Martine; Pietropaolo, Ermanno; Romano, Paolo
Bibcode: 2012SPIE.8448E..1SE
Altcode:
  We present an overview of the conceptual design of the data handling
  unit of the ECS, the Control System for the European Solar Telescope
  (EST). We will focus on describing the critical requirements for this
  unit resulting from the overall design of the telescope, together with
  its architecture and the results of the feasibility analysis carried
  out to date.

Title: A critical evaluation of the principal component analysis
    detection of polarized signatures using real stellar data
Authors: Paletou, F.
Bibcode: 2012A&A...544A...4P
Altcode: 2012arXiv1206.5139P
  The general context of this study is the post-processing of multiline
  spectropolarimetric observations of stars, and in particular the
  numerical analysis techniques aiming at detecting and characterizing
  polarized signatures. Using real observational data, we compare and
  clarify several points concerning various methods of analysis. We
  applied and compared the results of simple line addition, least-squares
  deconvolution, and denoising by principal component analysis to
  polarized stellar spectra available from the TBLegacy database of the
  Narval spectropolarimeter. This comparison of various approaches of
  distinct sophistication levels allows us to make a safe choice for the
  next implementation of on-line post-processing of our unique database
  for the stellar physics community.

Title: Laboratory Measurements of the Zeeman Effect in the - System
    of Iron Monohydride
Authors: Crozet, Patrick; Tourasse, Guillaume; Ross, Amanda J.;
   Tokaryk, D. W.; Paletou, Frederic; Ariste, Arturo Lopez
Bibcode: 2012mss..confERA09C
Altcode:
  We have used a hollow cathode sputtering source, flowing a mixture of 10
  % H_2 in Ar ∼45 standard cm^3/minute to form FeH radicals. Sputtering
  from iron required currents ≥ 250 mA. A permanent magnet was placed
  2--3 cm below the cathode, generating magnetic fields 3000--4500
  Gauss. Output from a Sirah Matisse Ti:sapphire laser was focused
  to a beamwaist &amp;lt; 1mm to probe a reasonably homogeneous
  region of the magnetic field, with the laser operating around 1
  μm for the 0-0 band and 890 nm for the 1-0 band of the F ^4Δ←X
  ^4Δ system in FeH. The magnetic field is calibrated to 0.5 %
  accuracy from the Zeeman response of the Ar I line at 10958.339
  cm<SUP>-1</SUP>. Several spectra have been taken for lines of the
  R branches of the F ^4Δ<SUB>7/2</SUB>←X ^4Δ<SUB>7/2</SUB> and F
  ^4Δ<SUB>5/2</SUB>←X ^4Δ<SUB>5/2</SUB> sub-bands, showing resolved
  structures at Doppler resolutions. Unresolved structures are seen
  for the Q and P transitions. Landé factors have been determined for
  the upper state (relying on ground state data from LMR work. <P />We
  gratefully acknowledge financial support from the French agency ANR,
  and from the CNRS (PNPS programme) for this work.}) either from fits
  to peak positions, or by simulating observed profiles when this was
  impossible. The Landé factors have been used to deduce a magnetic
  field of 2200 Gauss in sunspots from lines near 1 μm observed at
  the solar telescope THEMIS (Tenerife) in July 2011. Stokes V profiles
  were recorded at the telescope, for optimum sensitivity. The magnetic
  field deduced from atomic lines (Ti,Fe) is around 10 % higher than that
  found from FeH, compatible with molecules forming at higher altitudes
  in the solar atmosphere. <P />J.M. Brown, H. Korsgen, S.P. Beaton,
  &amp; K.M. Evenson, J. Chem. Phys. 124 234309 (2006)

Title: Long-term magnetic field monitoring of the Sun-like star ξ
    Bootis A
Authors: Morgenthaler, A.; Petit, P.; Saar, S.; Solanki, S. K.; Morin,
   J.; Marsden, S. C.; Aurière, M.; Dintrans, B.; Fares, R.; Gastine,
   T.; Lanoux, J.; Lignières, F.; Paletou, F.; Ramírez Vélez, J. C.;
   Théado, S.; Van Grootel, V.
Bibcode: 2012A&A...540A.138M
Altcode: 2011arXiv1109.5066M
  <BR /> Aims: We aim to investigate the long-term temporal evolution
  of the magnetic field of the solar-type star ξ Bootis A, both from
  direct magnetic field measurements and from the simultaneous estimate
  of indirect activity indicators. <BR /> Methods: We obtained seven
  epochs of high-resolution, circularly-polarized spectra from the
  NARVAL spectropolarimeter between 2007 and 2011, for a total of 76
  spectra. Using approximately 6100 photospheric spectral lines covering
  the visible domain, we employed a cross-correlation procedure to compute
  a mean polarized line profile from each spectrum. The large-scale
  photospheric magnetic field of the star was then modelled by means
  of Zeeman-Doppler Imaging, allowing us to follow the year-to-year
  evolution of the reconstructed magnetic topology. Simultaneously, we
  monitored the width of several magnetically sensitive spectral lines,
  the radial velocity, the line asymmetry of intensity line profiles,
  and the chromospheric emission in the cores of the Ca II H and Hα
  lines. <BR /> Results: During the highest observed activity states,
  in 2007 and 2011, the large-scale field of ξ Bootis A is almost
  completely axisymmetric and is dominated by its toroidal component. The
  toroidal component persists with a constant polarity, containing
  a significant fraction of the magnetic energy of the large-scale
  surface field through all observing epochs. The magnetic topologies
  reconstructed for these activity maxima are very similar, suggesting
  a form of short cyclicity in the large-scale field distribution. The
  mean unsigned large-scale magnetic flux derived from the magnetic
  maps varies by a factor of about 2 between the lowest and highest
  observed magnetic states. The chromospheric flux is less affected and
  varies by a factor of 1.2. Correlated temporal evolution, due to both
  rotational modulation and seasonal variability, is observed between
  the Ca II emission, the Hα emission and the width of magnetically
  sensitive lines. The rotational dependence of polarimetric magnetic
  measurements displays a weak correlation with other activity proxies,
  presumably due to the different spatial scales and centre-to-limb
  darkening associated with polarimetric signatures, as compared to
  non-polarized activity indicators. Better agreement is observed on the
  longer term. When measurable, the differential rotation reveals a strong
  latitudinal shear in excess of 0.2 rad d<SUP>-1</SUP>. <P />Based on
  observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi,
  France) of the Midi-Pyrénées Observatory, which is operated by the
  Institut National des Sciences de l'Univers of the Centre National de la
  Recherche Scientifique of France.Tables 3-6 are available in electronic
  form at <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: Laboratory determination of Landé factors for the molecular
    radical FeH
Authors: Crozet, P.; Tourasse, G.; Ross, A.; Paletou, F.; López
   Ariste, A.
Bibcode: 2012EAS....58...63C
Altcode:
  We report laboratory measurements of the Zeeman response of lines in the
  0-0 Wing-Ford band of the F-X system (λ ~ 1 μm) of FeH, measured in
  magnetic fields 0.3 - 0.5 Tesla. New Landé factors are used to deduce
  the magnetic field in sunspots from Stokes V profiles recorded at the
  solar telescope THEMIS. The magnetic field deduced from atomic lines
  (Ti, Fe) is slightly higher than that found from FeH.

Title: Data handling and control  of the European Solar Telescope
Authors: Ermolli, I.; Bettonvil, F.; Cauzzi, G.; Cavaller, L.;
   Collados, M.; Di Marcantonio, P.; Grivel, C.; Paletou, F.; Romano,
   P.; Aboudarham, J.; Cirami, R.; Cosentino, R.; Giorgi, F.; Lafon,
   M.; Laforgue, D.; Reardon, K.; Sliepen, G.
Bibcode: 2012MSAIS..19..380E
Altcode:
  We describe some aspects of the facility operation that have been
  considered for the design of the data handling and control of the
  European Solar Telescope. The main sub-systems of the EST relevant for
  the control are summarized, together with some information on current
  solar data models.

Title: Detection of a weak surface magnetic field on Sirius A:
    are all tepid stars magnetic?
Authors: Petit, P.; Lignières, F.; Aurière, M.; Wade, G. A.; Alina,
   D.; Ballot, J.; Böhm, T.; Jouve, L.; Oza, A.; Paletou, F.; Théado, S.
Bibcode: 2011A&A...532L..13P
Altcode: 2011arXiv1106.5363P
  <BR /> Aims: We aim at a highly sensitive search for weak magnetic
  fields in main sequence stars of intermediate mass, by scanning classes
  of stars with no previously reported magnetic members. After detecting a
  weak magnetic field on the normal, rapidly rotating A-type star Vega, we
  concentrate here on the bright star Sirius A, taken as a prototypical,
  chemically peculiar, moderately rotating Am star. <BR /> Methods: We
  employed the NARVAL and ESPaDOnS high-resolution spectropolarimeters
  to collect 442 circularly polarized spectra, complemented by 60
  linearly polarized spectra. Using a list of about 1100 photospheric
  spectral lines, we computed a cross correlation line profile from every
  spectrum, leading to a signal-to-noise ratio of up to 30 000 in the
  polarized profile. <BR /> Results: We report the repeated detection of
  circularly polarized, highly asymmetric signatures in the line profiles,
  interpreted as Zeeman signatures of a large-scale photospheric magnetic
  field, with a line-of-sight component equal to 0.2 ± 0.1 G. <BR />
  Conclusions: This is the first polarimetric detection of a surface
  magnetic field on an Am star. Using rough estimates of the physical
  properties of the upper layers of Sirius A, we suggest that a dynamo
  operating in the shallow convective envelope cannot account for
  the field strength reported here. Together with the magnetic field
  of Vega, this result confirms that a new class of magnetic objects
  exists among non Ap/Bp intermediate-mass stars, and it may indicate
  that a significant fraction of tepid stars are magnetic. <P />Based on
  observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi,
  France) of the Midi-Pyrénées Observatory, which is operated by the
  Institut National des Sciences de l'Univers of the Centre National de
  la Recherche Scientifique of France, and at the Canada-France-Hawaii
  Telescope (CFHT) which is operated by the National Research Council of
  Canada, the Institut National des Sciences de l'Univers of the Centre
  National de la Recherche Scientifique of France, and the University
  of Hawaii.

Title: Exploring the magnetic topologies of cool stars
Authors: Morin, J.; Donati, J. -F.; Petit, P.; Albert, L.; Auriére,
   M.; Cabanac, R.; Catala, C.; Delfosse, X.; Dintrans, B.; Fares,
   R.; Forveille, T.; Gastine, T.; Jardine, M.; Konstantinova-Antova,
   R.; Lanoux, J.; Lignires, F.; Morgenthaler, A.; Paletou, F.; Velez,
   J. C. Ramirez; Solanki, S. K.; Thado, S.; Van Grootel, V.
Bibcode: 2011IAUS..273..181M
Altcode: 2010arXiv1009.2589M
  Magnetic fields of cool stars can be directly investigated through
  the study of the Zeeman effect on photospheric spectral lines using
  several approaches. With spectroscopic measurement in unpolarised
  light, the total magnetic flux averaged over the stellar disc can
  be derived but very little information on the field geometry is
  available. Spectropolarimetry provides a complementary information
  on the large-scale magnetic topology. With Zeeman-Doppler Imaging
  (ZDI), this information can be retrieved to produce a map of the vector
  magnetic field at the surface of the star, and in particular to assess
  the relative importance of the poloidal and toroidal components as
  well as the degree of axisymmetry of the field distribution. <P />The
  development of high-performance spectropolarimeters associated with
  multi-lines techniques and ZDI allows us to explore magnetic topologies
  throughout the Hertzsprung-Russel diagram, on stars spanning a wide
  range of mass, age and rotation period. These observations bring novel
  constraints on magnetic field generation by dynamo effect in cool
  stars. In particular, the study of solar twins brings new insight on
  the impact of rotation on the solar dynamo, whereas the detection of
  strong and stable dipolar magnetic fields on fully convective stars
  questions the precise role of the tachocline in this process.

Title: Broyden's method for the solution of the multilevel non-LTE
    radiation transfer problem
Authors: Nicolas, S.; Bigarré, L.; Paletou, F.
Bibcode: 2011A&A...527A...1N
Altcode: 2010arXiv1012.3841N
  This study concerns the fast and accurate solution of multilevel
  non-LTE radiation transfer problems. We propose and evaluate an
  alternative iterative scheme to the classical MALI method. Our study
  is instead based on the application of Broyden's method for the
  solution of nonlinear systems of equations. Comparative tests, in 1D
  plane-parallel geometry, of the popular MALI method and our alternative
  method are discussed. The Broyden method is typically 4.5 times faster
  than MALI. This makes it also fairly competitive with the Gauss-Seidel
  and Successive Over-Relaxation methods developed after MALI.

Title: Polarized Line Formation in Multi-dimensional Media. II. A
    Fast Method to Solve Problems with Partial Frequency Redistribution
Authors: Anusha, L. S.; Nagendra, K. N.; Paletou, F.
Bibcode: 2011ApJ...726...96A
Altcode:
  In the previous paper of this series, we presented a formulation of
  the polarized radiative transfer equation for resonance scattering
  with partial frequency redistribution (PRD) in multi-dimensional
  media for a two-level atom model with unpolarized ground level, using
  the irreducible spherical tensors {T}^K_Q(i,Ω) for polarimetry. We
  also presented a polarized approximate lambda iteration method to
  solve this equation using the Jacobi iteration scheme. The formal
  solution used was based on a simple finite volume technique. In this
  paper, we develop a faster and more efficient method which uses the
  projection techniques applied to the radiative transfer equation (the
  Stabilized Preconditioned Bi-Conjugate Gradient method). We now use a
  more accurate formal solver, namely the well-known two-dimensional (2D)
  short characteristics method. Using the numerical method developed in
  Paper I, we can consider only simpler cases of finite 2D slabs due to
  computational limitations. Using the method developed in this paper,
  we could compute PRD solutions in 2D media in the more difficult
  context of semi-infinite 2D slabs also. We present several solutions
  which may serve as benchmarks in future studies in this area.

Title: Data handling and control for the European Solar Telescope
Authors: Ermolli, Ilaria; Bettonvil, Felix; Cauzzi, Gianna; Cavaller,
   Lluis; Collados, Manuel; Di Marcantonio, Paolo; Paletou, Frederic;
   Romano, Paolo; Aboudarham, Jean; Cirami, Roberto; Cosentino, Rosario;
   Giorgi, Fabrizio; Lafon, Martine; Laforgue, Didier; Reardon, Kevin;
   Sliepen, Guus
Bibcode: 2010SPIE.7740E..0GE
Altcode: 2010SPIE.7740E..13E
  We introduce the concepts for the control and data handling systems of
  the European Solar Telescope (EST), the main functional and technical
  requirements for the definition of these systems, and the outcomes
  from the trade-off analysis to date. Concerning the telescope control,
  EST will have performance requirements similar to those of current
  medium-sized night-time telescopes. On the other hand, the science
  goals of EST require the simultaneous operation of three instruments
  and of a large number of detectors. This leads to a projected data
  flux that will be technologically challenging and exceeds that of
  most other astronomical projects. We give an overview of the reference
  design of the control and data handling systems for the EST to date,
  focusing on the more critical and innovative aspects resulting from
  the overall design of the telescope.

Title: Magnetic field and velocity of early M dwarfs (Donati+, 2008)
Authors: Donati, J. -F.; Morin, J.; Petit, P.; Delfosse, X.; Forveille,
   T.; Auriere, M.; Cabanac, R.; Dintrans, B.; Fares, R.; Gastine, T.;
   Jardine, M. M.; Lignieres, F.; Paletou, F.; Ramirez Velez, J. C.;
   Theado, S.
Bibcode: 2010yCat..73900545D
Altcode:
  Spectropolarimetric observations of the selected M dwarfs were collected
  with NARVAL and the 2m Telescope Bernard Lyot (TBL), between 2007
  January and 2008 February (in three different runs). <P />(2 data
  files).

Title: Magnetic field and velocity of early M dwarfs (Morin+, 2008)
Authors: Morin, J.; Donati, J. -F.; Petit, P.; Delfosse, X.; Forveille,
   T.; Albert, L.; Auriere, M.; Cabanac, R.; Dintrans, B.; Fares, R.;
   Gastine, T.; Jardine, M. M.; Lignieres, F.; Paletou, F.; Ramirez Velez,
   J. C.; Theado, S.
Bibcode: 2010yCat..73900567M
Altcode:
  We have collected 107 pairs of Stokes I (unpolarised) and V
  (circularly polarised) spectra with the twin instruments ESPaDOnS at
  CFHT (2003ASPC..307...41D) and NARVAL at TBL between January 2006
  and February 2008. All spectra were reduced using the Libre-Esprit
  pipeline, and the mean I and V line profiles were extracted using the
  Least-Squares Deconvolution (LSD) technique (1997MNRAS.291..658D). The
  star V374 Peg (2008MNRAS.384...77M) is also included in the discussion
  and in table1.dat. <P />(2 data files).

Title: A conjugate gradient method for solving the non-LTE line
    radiation transfer problem
Authors: Paletou, F.; Anterrieu, E.
Bibcode: 2009A&A...507.1815P
Altcode: 2009arXiv0905.3258P
  This study concerns the fast and accurate solution of the line radiation
  transfer problem, under non-LTE conditions. We propose and evaluate an
  alternative iterative scheme to the classical ALI-Jacobi method, and to
  the more recently proposed Gauss-Seidel and successive over-relaxation
  (GS/SOR) schemes. Our study is indeed based on applying a preconditioned
  bi-conjugate gradient method (BiCG-P). Standard tests, in 1D plane
  parallel geometry and in the frame of the two-level atom model with
  monochromatic scattering are discussed. Rates of convergence between
  the previously mentioned iterative schemes are compared, as are their
  respective timing properties. The smoothing capability of the BiCG-P
  method is also demonstrated.

Title: Preconditioned Bi-conjugate Gradient Method for Radiative
    Transfer in Spherical Media
Authors: Anusha, L. S.; Nagendra, K. N.; Paletou, F.; Léger, L.
Bibcode: 2009ApJ...704..661A
Altcode: 2009arXiv0906.2926A
  A robust numerical method called the Preconditioned Bi-Conjugate
  Gradient (Pre-BiCG) method is proposed for the solution of the radiative
  transfer equation in spherical geometry. A variant of this method called
  Stabilized Preconditioned Bi-Conjugate Gradient (Pre-BiCG-STAB) is also
  presented. These are iterative methods based on the construction of a
  set of bi-orthogonal vectors. The application of the Pre-BiCG method
  in some benchmark tests shows that the method is quite versatile,
  and can handle difficult problems that may arise in astrophysical
  radiative transfer theory.

Title: Multi-Line Stokes Inversion for Prominence Magnetic-Field
    Diagnostics
Authors: Casini, R.; López Ariste, A.; Paletou, F.; Léger, L.
Bibcode: 2009ApJ...703..114C
Altcode: 2009arXiv0906.2144C
  We present test results on the simultaneous inversion of the Stokes
  profiles of the He I lines at 587.6 nm (D<SUB>3</SUB>) and 1083.0 nm
  in prominences (90° scattering). We created data sets of synthetic
  Stokes profiles for the case of quiescent prominences (B &lt; 200 G),
  assuming a conservative value of 10<SUP>-3</SUP> of the peak intensity
  for the polarimetric sensitivity of the simulated observations. In
  this work, we focus on the error analysis for the inference of the
  magnetic field vector, under the usual assumption that the prominence
  can be assimilated to a slab of finite optical thickness with uniform
  magnetic and thermodynamic properties. We find that the simultaneous
  inversion of the two lines significantly reduces the errors on the
  inference of the magnetic field vector, with respect to the case of
  single-line inversion. These results provide a solid justification for
  current and future instrumental efforts with multi-line capabilities
  for the observations of solar prominences and filaments.

Title: Freeware Solutions for Spectropolarimetric Data Reduction
Authors: Paletou, F.; Rezaei, R.; Léger, L.
Bibcode: 2009ASPC..405...51P
Altcode:
  Most of the solar physicists use very expensive software for data
  reduction and visualization. We present hereafter a reliable freeware
  solution based on the Python language. This is made possible by the
  association of the latter with a small set of additional libraries
  developed in the scientific community. It provides then a very powerful
  and economical alternative to other interactive data languages. Although
  it can also be used for any kind of post-processing of data, we
  demonstrate the capabilities of such a set of freeware tools using
  THéMIS observations of the second solar spectrum.

Title: The Ground-Based Solar Observations Database BASS 2000
Authors: Paletou, F.; Lafon, M.; Maeght, P.; Grimaud, F.; Louge, T.;
   Aboudarham, J.
Bibcode: 2009ASPC..405..397P
Altcode:
  BASS 2000 is the French solar database for ground-based instruments. We
  describe hereafter our organization, our tasks and the products we can
  deliver to the international community. Our prospects cover data mining
  into the THéMIS archive, a participation to the EST endeavour and the
  creation and curation of the ESPaDOnS/NARVAL stellar spectra database.

Title: Why are Some A Stars Magnetic, while Most are Not?
Authors: Wade, G. A.; Silvester, J.; Bale, K.; Johnson, N.; Power, J.;
   Aurière, M.; Ligniéres, F.; Dintrans, B.; Donati, J. -F.; Hui Bon
   Hoa, A.; Mouillet, D.; Naseri, S.; Paletou, F.; Petit, P.; Rincon, F.;
   Toque, N.; Bagnulo, S.; Folsom, C. P.; Landstreet, J. D.; Gruberbauer,
   M.; Lueftinger, T.; Jeffers, S. V.; Lèbre, A.; Marsden, S. C.
Bibcode: 2009ASPC..405..499W
Altcode:
  A small fraction of intermediate-mass main sequence (A and B type)
  stars have strong, organised magnetic fields. The large majority
  of such stars, however, show no evidence for magnetic fields, even
  when observed with very high precision. In this paper we describe a
  simple model, motivated by qualitatively new observational results,
  that provides a natural physical explanation for the small fraction
  of observed magnetic stars.

Title: 2D Radiative Modeling of He I Spectral Lines Formed in Solar
    Prominences
Authors: Léger, L.; Paletou, F.
Bibcode: 2009ASPC..405..325L
Altcode:
  We present preliminary results of 2D radiative modeling of He I lines
  in solar prominences, using a new numerical code developed by us
  \citep*{leger_leger07}. It treats self-consistently the radiation
  transfer and the non-LTE statistical equilibrium of H and, in a
  second stage, the one of He using a detailed atomic model. Preliminary
  comparisons with new visible plus near-infrared observations made at
  high spectral resolution with THéMIS are very satisfactory.

Title: 2D non-LTE radiative modelling of He I spectral lines formed
    in solar prominences
Authors: Léger, L.; Paletou, F.
Bibcode: 2009A&A...498..869L
Altcode: 2008arXiv0811.4753L
  Context: The interpretation of high-resolution spectropolarimetric
  observations of solar prominences completed primarily at visible and
  near-infrared wavelengths, requires radiative modelling that takes
  into account both multi-dimensional geometry and complex atomic
  models. <BR />Aims: We enhance the interpretation of observations
  of He i multiplets, by considering 2D non-LTE unpolarized radiation
  transfer, and taking into account of the atomic fine-structure of
  helium. <BR />Methods: We apply our 2D non-LTE radiative transfer
  code, which is based on the multi-grid Gauss-Seidel/SOR iterative
  schemes. <BR />Results: It allows us to compute realistic emergent
  intensity profiles for the He i λ 10 830 Å and D<SUB>3</SUB>
  multiplets, which can be directly compared to the simultaneous and
  high-resolution observations completed at THéMIS. A preliminary 2D
  multi-thread modelling is also discussed.

Title: Magnetic geometries of Sun-like stars: exploring the
    mass-rotation plane
Authors: Petit, Pascal; Dintrans, B.; Aurière, M.; Catala, C.; Donati,
   J. -F.; Fares, R.; Gastine, T.; Lignières, F.; Morgenthaler, A.;
   Morin, J.; Paletou, F.; Ramirez Velez, J.; Solanki, S. K.; Théado, S.
Bibcode: 2009IAUS..259..441P
Altcode:
  Sun-like stars are able to continuously generate a large-scale
  magnetic field through the action of a dynamo. Various physical
  parameters of the star are able to affect the dynamo output, in
  particular the rotation and mass. Using the NARVAL spectropolarimeter
  (Observatoire du Pic du Midi, France), it is now possible to measure
  the large-scale magnetic field of solar analogues (i.e. stars very
  close to the Sun in the mass-rotation plane, including strict solar
  twins). From spectropolarimetric time-series, tomographic inversion
  enables one to reconstruct the field geometry and its progressive
  distortion under the effect of surface differential rotation. We
  show the first results obtained on a sample of main-sequence dwarfs,
  probing masses between 0.7 and 1.4 solar mass and rotation rates
  between 1 and 3 solar rotation rate.

Title: Magnetic geometries of Sun-like stars : impact of rotation
Authors: Petit, P.; Dintrans, B.; Aurière, M.; Catala, C.; Donati,
   J. -F.; Fares, R.; Gastine, T.; Lignières, F.; Morin, J.; Paletou,
   F.; Ramirez, J.; Solanki, S. K.; Théado, S.
Bibcode: 2008sf2a.conf..523P
Altcode:
  Sun-like stars are able to continuously generate a large-scale magnetic
  field through the action of a dynamo. Various physical parameters
  of the star are able to affect the dynamo output, in particular the
  rotation and mass. Using new generation stellar spectropolarimeters
  (ESPaDOnS@CFHT, NARVAL@TBL), it is now possible to measure the
  large-scale magnetic field of solar analogues (i.e. stars very close
  to the Sun in the stellar-parameter plane, including strict solar
  twins). From spectropolarimetric time-series, tomographic inversion
  of polarized Zeeman signatures allows us to reconstruct the field
  geometry and its progressive distortion under the effect of surface
  differential rotation. We detail the first results obtained on a sample
  of four main-sequence dwarfs, with masses close to 1 solar mass and
  rotation rates between 1 and 3 solar rotation rate.

Title: The magnetic field of solar prominences.
Authors: Paletou, F.
Bibcode: 2008sf2a.conf..559P
Altcode: 2008arXiv0810.2662P
  In his famous monographs, Einar Tandberg-Hanssen writes that ``the
  single, physically most important parameter to study in prominences may
  be the magnetic field. Shapes, motions, and in fact the very existence
  of prominences depend on the nature of the magnetic field threading
  the prominence plasma''. Hereafter we sumarize recent contributions
  and advances in our knowledge about the magnetic field of solar
  prominences. It mostly relies on high resolution and high sensitivity
  spectropolarimetry made both in the visible and in the near infrared.

Title: Large-scale magnetic topologies of early M dwarfs
Authors: Donati, J. -F.; Morin, J.; Petit, P.; Delfosse, X.; Forveille,
   T.; Aurière, M.; Cabanac, R.; Dintrans, B.; Fares, R.; Gastine, T.;
   Jardine, M. M.; Lignières, F.; Paletou, F.; Ramirez Velez, J. C.;
   Théado, S.
Bibcode: 2008MNRAS.390..545D
Altcode: 2008MNRAS.tmp.1077D; 2008arXiv0809.0269D
  We present here additional results of a spectropolarimetric survey of
  a small sample of stars ranging from spectral type M0 to M8 aimed at
  investigating observationally how dynamo processes operate in stars
  on both sides of the full convection threshold (spectral type M4). <P
  />The present paper focuses on early M stars (M0-M3), that is above
  the full convection threshold. Applying tomographic imaging techniques
  to time series of rotationally modulated circularly polarized profiles
  collected with the NARVAL spectropolarimeter, we determine the rotation
  period and reconstruct the large-scale magnetic topologies of six early
  M dwarfs. We find that early-M stars preferentially host large-scale
  fields with dominantly toroidal and non-axisymmetric poloidal
  configurations, along with significant differential rotation (and
  long-term variability); only the lowest-mass star of our subsample is
  found to host an almost fully poloidal, mainly axisymmetric large-scale
  field resembling those found in mid-M dwarfs. <P />This abrupt change in
  the large-scale magnetic topologies of M dwarfs (occurring at spectral
  type M3) has no related signature on X-ray luminosities (measuring
  the total amount of magnetic flux); it thus suggests that underlying
  dynamo processes become more efficient at producing large-scale fields
  (despite producing the same flux) at spectral types later than M3. We
  suspect that this change relates to the rapid decrease in the radiative
  cores of low-mass stars and to the simultaneous sharp increase of the
  convective turnover times (with decreasing stellar mass) that models
  predict to occur at M3; it may also be (at least partly) responsible for
  the reduced magnetic braking reported for fully convective stars. <P
  />Based on observations obtained at the Télescope Bernard Lyot
  (TBL), operated by the Institut National des Science de l'Univers
  of the Centre National de la Recherche Scientifique of France. <P
  />E-mail: donati@ast.obs-mip.fr (J-FD); jmorin@ast.obs-mip.fr (JM);
  petit@ast.obs-mip.fr (PP); xavier.delfosse@obs.ujf-grenoble.fr (XD);
  thierry.forveille@obs.ujf-grenoble.fr (TF); auriere@ast.obs-mip.fr
  (MA); remi.cabanac@ast.obs-mip.fr (RC); dintrans@ast.obs-mip.fr
  (BD); rfares@ast.obs-mip.fr (RF); tgastine@ast.obs-mip.fr
  (TG); mmj@st-and.ac.uk (MMJ); lignieres@ast.obs-mip.fr (FL);
  fpaletou@ast.obs-mip.fr (FP); julio.ramirez@obspm.fr (JCRV);
  sylvie.theado@ast.obs-mip.fr (ST)

Title: Large-scale magnetic topologies of mid M dwarfs
Authors: Morin, J.; Donati, J. -F.; Petit, P.; Delfosse, X.; Forveille,
   T.; Albert, L.; Aurière, M.; Cabanac, R.; Dintrans, B.; Fares, R.;
   Gastine, T.; Jardine, M. M.; Lignières, F.; Paletou, F.; Ramirez
   Velez, J. C.; Théado, S.
Bibcode: 2008MNRAS.390..567M
Altcode: 2008arXiv0808.1423M; 2008MNRAS.tmp.1071M
  We present in this paper, the first results of a spectropolarimetric
  analysis of a small sample (~20) of active stars ranging from spectral
  type M0 to M8, which are either fully convective or possess a very
  small radiative core. This study aims at providing new constraints
  on dynamo processes in fully convective stars. <P />This paper
  focuses on five stars of spectral type ~M4, i.e. with masses close
  to the full convection threshold (~=0.35M<SUB>solar</SUB>), and with
  short rotational periods. Tomographic imaging techniques allow us
  to reconstruct the surface magnetic topologies from the rotationally
  modulated time-series of circularly polarized profiles. We find that
  all stars host mainly axisymmetric large-scale poloidal fields. Three
  stars were observed at two different epochs separated by ~1 yr; we find
  the magnetic topologies to be globally stable on this time-scale. <P
  />We also provide an accurate estimation of the rotational period of
  all stars, thus allowing us to start studying how rotation impacts
  the large-scale magnetic field. <P />Based on observations obtained at
  the Canada-France-Hawaii Telescope (CFHT) and the Télescope Bernard
  Lyot (TBL). CFHT is operated by the National Research Council of
  Canada, the Institut National des Science de l'Univers of the Centre
  National de la Recherche Scientifique of France (INSU/CNRS) and the
  University of Hawaii, while the TBL is operated by CNRS/INSU. <P
  />E-mail: jmorin@ast.obs-mip.fr (JM); donati@ast.obs-mip.fr (J-FD);
  petit@ast.obs-mip.fr (PP); xavier.delfosse@obs.ujf-grenoble.fr (XD);
  thierry.forveille@obs.ujf-grenoble.fr (TF); albert@cfht.hawaii.edu
  (LA); auriere@ast.obs-mip.fr (MA); remi.cabanac@ast.obs-mip.fr
  (RC); dintrans@ast.obs-mip.fr (BD); rfares@ast.obs-mip.fr (RF);
  tgastine@ast.obs-mip.fr (TG); mmj@st-andrews.ac.uk (MMJ);
  ligniere@ast.obs-mip.fr (FL); fpaletou@ast.obs-mip.fr (FP);
  jramirez@mesiog.obspm.fr (JR); sylvie.theado@ast.obs-mip.fr (ST)

Title: Toroidal versus poloidal magnetic fields in Sun-like stars:
    a rotation threshold
Authors: Petit, P.; Dintrans, B.; Solanki, S. K.; Donati, J. -F.;
   Aurière, M.; Lignières, F.; Morin, J.; Paletou, F.; Ramirez Velez,
   J.; Catala, C.; Fares, R.
Bibcode: 2008MNRAS.388...80P
Altcode: 2008MNRAS.tmp..715P; 2008arXiv0804.1290P
  From a set of stellar spectropolarimetric observations, we report
  the detection of surface magnetic fields in a sample of four
  solar-type stars, namely HD 73350, HD 76151, HD 146233 (18 Sco) and HD
  190771. Assuming that the observed variability of polarimetric signal
  is controlled by stellar rotation, we establish the rotation periods of
  our targets, with values ranging from 8.8 d (for HD 190771) to 22.7 d
  (for HD 146233). Apart from rotation, fundamental parameters of the
  selected objects are very close to the Sun's, making this sample
  a practical basis to investigate the specific impact of rotation
  on magnetic properties of Sun-like stars. <P />We reconstruct the
  large-scale magnetic geometry of the targets as a low-order (l &lt; 10)
  spherical harmonic expansion of the surface magnetic field. From the set
  of magnetic maps, we draw two main conclusions. (i) The magnetic energy
  of the large-scale field increases with rotation rate. The increase
  in chromospheric emission with the mean magnetic field is flatter than
  observed in the Sun. Since the chromospheric flux is also sensitive to
  magnetic elements smaller than those contributing to the polarimetric
  signal, this observation suggests that a larger fraction of the surface
  magnetic energy is stored in large scales as rotation increases. (ii)
  Whereas the magnetic field is mostly poloidal for low rotation rates,
  more rapid rotators host a large-scale toroidal component in their
  surface field. From our observations, we infer that a rotation period
  lower than ~12 d is necessary for the toroidal magnetic energy to
  dominate over the poloidal component.

Title: Magnetospheric accretion on the T Tauri star BP Tauri
Authors: Donati, J. -F.; Jardine, M. M.; Gregory, S. G.; Petit, P.;
   Paletou, F.; Bouvier, J.; Dougados, C.; Ménard, F.; Collier Cameron,
   A.; Harries, T. J.; Hussain, G. A. J.; Unruh, Y.; Morin, J.; Marsden,
   S. C.; Manset, N.; Aurière, M.; Catala, C.; Alecian, E.
Bibcode: 2008MNRAS.386.1234D
Altcode: 2008MNRAS.tmp..461D; 2008arXiv0802.2052D
  From observations collected with the ESPaDOnS and NARVAL
  spectropolarimeters, we report the detection of Zeeman signatures
  on the classical T Tauri star (cTTS) BP Tau. Circular polarization
  signatures in photospheric lines and in narrow emission lines
  tracing magnetospheric accretion are monitored throughout most of
  the rotation cycle of BP Tau at two different epochs in 2006. We
  observe that rotational modulation dominates the temporal variations
  of both unpolarized and circularly polarized spectral proxies tracing
  the photosphere and the footpoints of accretion funnels. <P />From
  the complete data sets at each epoch, we reconstruct the large-scale
  magnetic topology and the location of accretion spots at the surface
  of BP Tau using tomographic imaging. We find that the field of BP Tau
  involves a 1.2 kG dipole and 1.6 kG octupole, both slightly tilted with
  respect to the rotation axis. Accretion spots coincide with the two main
  magnetic poles at high latitudes and overlap with dark photospheric
  spots; they cover about 2 per cent of the stellar surface. The strong
  mainly axisymmetric poloidal field of BP Tau is very reminiscent
  of magnetic topologies of fully convective dwarfs. It suggests that
  magnetic fields of fully convective cTTSs such as BP Tau are likely not
  fossil remants, but rather result from vigorous dynamo action operating
  within the bulk of their convective zones. <P />Preliminary modelling
  suggests that the magnetosphere of BP Tau extends to distances of at
  least 4R<SUB>*</SUB> to ensure that accretion spots are located at high
  latitudes, and is not blown open close to the surface by a putative
  stellar wind. It apparently succeeds in coupling to the accretion
  disc as far out as the corotation radius, and could possibly explain
  the slow rotation of BP Tau. <P />Based on observations obtained
  at the Canada-France-Hawaii Telescope (CFHT) and at the Télescope
  Bernard Lyot (TBL). CFHT is operated by the National Research Council
  of Canada, the Institut National des Sciences de l'Univers of the
  Centre National de la Recherche Scientifique of France (INSU/CNRS)
  and the University of Hawaii, while TBL is operated by CNRS/INSU. <P
  />E-mail: donati@ast.obs-mip.fr (J-FD); mmj@st-andrews.ac.uk
  (MMJ); sg64@st-andrews.ac.uk (SGG); petit@ast.obs-mip.fr (PP);
  fpaletou@ast.obs-mip.fr (FP); jerome.bouvier@obs.ujf-grenoble.fr
  (JB); catherine.dougados@obs.ujf-grenoble.fr (CD);
  francois.menard@obs.ujf-grenoble.fr (FM); acc4@st-andrews.ac.uk
  (ACC); th@astro.ex.ac.uk (TJH); ghussain@eso.org (GAJH);
  y.unruh@imperial.ac.uk (YU); jmorin@ast.obs-mip.fr (JM); scm@aao.gov.au
  (SCM); manset@cfht.hawaii.edu (NM); auriere@ast.obs-mip.fr (MA);
  claude.catala@obspm.fr (CC); evelyne.alecian@obspm.fr (EA)

Title: Magnetic Topologies of Cool Stars
Authors: Donati, J. -F.; Jardine, M. M.; Petit, P.; Morin, J.; Bouvier,
   J.; Collier Cameron, A.; Delfosse, X.; Dintrans, B.; Dobler, W.;
   Dougados, C.; Ferreira, J.; Forveille, T.; Gregory, S. G.; Harries,
   T.; Hussain, G. A. J.; Menard, F.; Paletou, F.
Bibcode: 2008ASPC..384..156D
Altcode: 2007astro.ph..2159D; 2008csss...14..156D
  Stellar magnetic fields can be investigated using several, very
  complementary approaches. While conventional spectroscopy is capable of
  estimating the average magnetic strength of potentially complex field
  configurations thanks to its low sensitivity to the vector properties
  of the field, spectropolarimetry can be used to map the medium-
  and large-scale structure of magnetic topologies. In particular, the
  latter approach allows one to retrieve information about the poloidal
  and toroidal components of the large-scale dynamo fields in low-mass
  stars, and thus to investigate the physical processes that produce
  them. Similarly, this technique can be used to explore how magnetic
  fields couple young stars to their massive accretion disc and thus
  to estimate how much mass and angular momentum are transfered to the
  newly-born low-mass star. We present here the latest results in this
  field obtained with spectropolarimetry, with special emphasis on the
  surprising discoveries obtained on very-low mass fully-convective stars
  and classical T Tauri stars thanks to the ESPaDOnS spectropolarimeter
  recently installed on the 3.6m Canada-France-Hawaii Telescope.

Title: Weak magnetic fields in Ap/Bp stars. Evidence for a dipole
    field lower limit and a tentative interpretation of the magnetic
    dichotomy
Authors: Aurière, M.; Wade, G. A.; Silvester, J.; Lignières, F.;
   Bagnulo, S.; Bale, K.; Dintrans, B.; Donati, J. F.; Folsom, C. P.;
   Gruberbauer, M.; Hui Bon Hoa, A.; Jeffers, S.; Johnson, N.; Landstreet,
   J. D.; Lèbre, A.; Lueftinger, T.; Marsden, S.; Mouillet, D.; Naseri,
   S.; Paletou, F.; Petit, P.; Power, J.; Rincon, F.; Strasser, S.;
   Toqué, N.
Bibcode: 2007A&A...475.1053A
Altcode: 2007arXiv0710.1554A
  Aims:We investigated a sample of 28 well-known
  spectroscopically-identified magnetic Ap/Bp stars, with weak,
  poorly-determined or previously undetected magnetic fields. The
  aim of this study is to explore the weak part of the magnetic field
  distribution of Ap/Bp stars. <BR />Methods: Using the MuSiCoS and
  NARVAL spectropolarimeters at Télescope Bernard Lyot (Observatoire
  du Pic du Midi, France) and the cross-correlation technique Least
  Squares Deconvolution (LSD), we obtained 282 LSD Stokes V signatures
  of our 28 sample stars, in order to detect the magnetic field and
  to infer its longitudinal component with high precision (median
  σ=40 G). <BR />Results: For the 28 studied stars, we obtained
  27 detections of Stokes V Zeeman signatures from the MuSiCoS
  observations. Detection of the Stokes V signature of the 28th star
  (HD 32650) was obtained during science demonstration time of the new
  NARVAL spectropolarimeter at Pic du Midi. This result clearly shows
  that when observed with sufficient precision, all firmly classified
  Ap/Bp stars show detectable surface magnetic fields. Furthermore,
  all detected magnetic fields correspond to longitudinal fields which
  are significantly greater than some tens of G. To better characterise
  the surface magnetic field intensities and geometries of the sample,
  we phased the longitudinal field measurements of each star using
  new and previously-published rotational periods, and modeled them to
  infer the dipolar field intensity (B_d, measured at the magnetic pole)
  and the magnetic obliquity (β). The distribution of derived dipole
  strengths for these stars exhibits a plateau at about 1 kG, falling off
  to larger and smaller field strengths. Remarkably, in this sample of
  stars selected for their presumably weak magnetic fields, we find only
  2 stars for which the derived dipole strength is weaker than 300 G. We
  interpret this “magnetic threshold” as a critical value necessary
  for the stability of large-scale magnetic fields, and develop a simple
  quantitative model that is able to approximately reproduce the observed
  threshold characteristics. This scenario leads to a natural explanation
  of the small fraction of intermediate-mass magnetic stars. It may also
  explain the near-absence of magnetic fields in more massive B and O-type
  stars. <P />Based on data obtained using the Télescope Bernard Lyot
  at Observatoire du Pic du Midi, CNRS and Université Paul Sabatier,
  France. Figures 7 to 32 are only available in electronic form at
  http://www.aanda.org Table 3 is only available in electronic form
  at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
  or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/475/1053

Title: 2D radiative modelling of He I spectral lines formed in
    solar prominences
Authors: Leger, L.; Paletou, F.
Bibcode: 2007arXiv0712.1701L
Altcode:
  We present preliminary results of 2D radiative modelling of He I
  lines in solar prominences, using a new numerical code developed by us
  (Leger, Chevallier and Paletou 2007). It treats self-consistently the
  radiation transfer and the non-LTE statistical equilibrium of H and, in
  a second stage, the one of He using a detailed atomic model. Preliminary
  comparisons with new visible plus near-infrared observations made at
  high spectral resolution with THeMIS are very satisfactory.

Title: Freeware solutions for spectropolarimetric data reduction
Authors: Paletou, F.; Rezaei, R.; Leger, L.
Bibcode: 2007arXiv0712.1522P
Altcode:
  Most of the solar physicists use very expensive software for
  data reduction and visualization. We present hereafter a reliable
  freeware solution based on the Python language. This is made possible
  by the association of the latter with a small set of additional
  libraries developed in the scientific community. It provides then
  a very powerful and economical alternative to other interactive data
  languages. Although it can also be used for any kind of post-processing
  of data, we demonstrate the capabities of such a set of freeware tools
  using THeMIS observations of the second solar spectrum.

Title: Why are some A stars magnetic, while most are not?
Authors: Wade, G. A.; Silvester, J.; Bale, K.; Johnson, N.; Power, J.;
   Aurière, M.; Ligniéres, F.; Dintrans, B.; Donati, J. -F.; Bon Hoa,
   A. Hui; Mouillet, D.; Naseri, S.; Paletou, F.; Petit, P.; Rincon, F.;
   Toque, N.; Bagnulo, S.; Folsom, C. P.; Landstreet, J. D.; Gruberbauer,
   M.; Lueftinger, T.; Jeffers, S.; Lèbre, A.; Marsden, S.
Bibcode: 2007arXiv0712.3614W
Altcode:
  A small fraction of intermediate-mass main sequence (A and B type)
  stars have strong, organised magnetic fields. The large majority
  of such stars, however, show no evidence for magnetic fields, even
  when observed with very high precision. In this paper we describe a
  simple model, motivated by qualitatively new observational results,
  that provides a natural physical explanation for the small fraction
  of observed magnetic stars.

Title: The ground-based solar observations database BASS 2000
Authors: Paletou, F.; Lafon, M.; Maeght, P.; Grimaud, F.; Louge, T.;
   Aboudarham, J.
Bibcode: 2007arXiv0712.2421P
Altcode:
  BASS 2000 is the French solar database for ground-based instruments. We
  describe hereafter our organization, our tasks and the products we can
  deliver to the international community. Our prospects cover data mining
  into the THeMIS archive, a participation to the EST endeavour and the
  creation and curation of the ESPaDOnS/NARVAL stellar spectra database.

Title: Magnetic fields and accretion flows on the classical T Tauri
    star V2129 Oph
Authors: Donati, J. -F.; Jardine, M. M.; Gregory, S. G.; Petit, P.;
   Bouvier, J.; Dougados, C.; Ménard, F.; Collier Cameron, A.; Harries,
   T. J.; Jeffers, S. V.; Paletou, F.
Bibcode: 2007MNRAS.380.1297D
Altcode: 2007MNRAS.tmp..760D; 2007arXiv0709.1414D
  From observations collected with the ESPaDOnS spectropolarimeter, we
  report the discovery of magnetic fields at the surface of the mildly
  accreting classical T Tauri star (cTTS) V2129 Oph. Zeeman signatures
  are detected, both in photospheric lines and in the emission lines
  formed at the base of the accretion funnels linking the disc to the
  protostar, and monitored over the whole rotation cycle of V2129 Oph. We
  observe that rotational modulation dominates the temporal variations
  of both unpolarized and circularly polarized line profiles. <P />We
  reconstruct the large-scale magnetic topology at the surface of V2129
  Oph from both sets of Zeeman signatures simultaneously. We find it
  to be rather complex, with a dominant octupolar component and a weak
  dipole of strengths 1.2 and 0.35 kG, respectively, both slightly tilted
  with respect to the rotation axis. The large-scale field is anchored in
  a pair of 2-kG unipolar radial field spots located at high latitudes
  and coinciding with cool dark polar spots at photospheric level. This
  large-scale field geometry is unusually complex compared to those of
  non-accreting cool active subgiants with moderate rotation rates. <P
  />As an illustration, we provide a first attempt at modelling the
  magnetospheric topology and accretion funnels of V2129 Oph using
  field extrapolation. We find that the magnetosphere of V2129 Oph
  must extend to about 7R<SUB>*</SUB> to ensure that the footpoints
  of accretion funnels coincide with the high-latitude accretion
  spots on the stellar surface. It suggests that the stellar magnetic
  field succeeds in coupling to the accretion disc as far out as the
  corotation radius, and could possibly explain the slow rotation of V2129
  Oph. The magnetospheric geometry we derive qualitatively reproduces the
  modulation of Balmer lines and produces X-ray coronal fluxes typical
  of those observed in cTTSs. <P />Based on observations obtained at
  the Canada-France-Hawaii Telescope (CFHT) which is operated by the
  National Research Council of Canada, the Institut National des Sciences
  de l'Univers of the Centre National de la Recherche Scientifique of
  France, and the University of Hawaii. <P />E-mail: donati@ast.obs-mip.fr
  (J-FD); mmj@st-andrews.ac.uk (MMJ); sg64@st-andrews.ac.uk (SGG);
  petit@ast.obs-mip.fr (PP); jerome.bouvier@obs.ujf-grenoble.fr
  (JB); catherine.dougados@obs.ujf-grenoble.fr (CD);
  francois.menard@obs.ujf-grenoble.fr (FM); acc4@st-andrews.ac.uk
  (ACC); th@astro.ex.ac.uk (TJH); s.v.jeffers@phys.uu.nl (SVJ);
  fpaletou@ast.obs-mip.fr (FP)

Title: VizieR Online Data Catalog: Magnetic fields in Ap/Bp stars
    (Auriere+, 2007)
Authors: Auriere, M.; Wade, G. A.; Silvester, J.; Lignieres, F.;
   Bagnulo, S.; Bale, K.; Dintrans, B.; Donati, J. F.; Folsom, C. P.;
   Gruberbauer, M.; Hui Bon Hoa, A.; Jeffers, S.; Johnson, N.; Landstreet,
   J. D.; Lebre, A.; Lueftinger, T.; Marsden, S.; Mouillet, D.; Naseri,
   S.; Paletou, F.; Petit, P.; Power, J.; Rincon, F.; Strasser, S.;
   Toque, N.
Bibcode: 2007yCat..34751053A
Altcode:
  We have investigated a sample of 28 well-known
  spectroscopically-identified magnetic Ap/Bp stars, with weak,
  poorly-determined or previously undetected magnetic fields. The
  aim of this study is to explore the weak part of the magnetic
  field distribution of Ap/Bp stars. Using the MuSiCoS and NARVAL
  spectropolarimeters at Telescope Bernard Lyot (Observatoire du Pic
  du Midi, France) and the cross-correlation technique Least Squares
  Deconvolution (LSD), we have obtained 282 LSD Stokes $V$ signatures of
  our 28 sample stars, in order to detect the magnetic field and to infer
  its longitudinal component with high precision (median sigma=40G). <P
  />(2 data files).

Title: Multidimensional NLTE Radiative Transfer
Authors: Léger, L.; Paletou, F.; Navarre, F.
Bibcode: 2007sf2a.conf..592L
Altcode:
  We present the main capabilities and performances of a new 2D
  numerical radiative transfer code (Léger et al. 2007). It treats
  self-consistently the radiative transfer and the NLTE statistical
  equilibrium of H. It includes also the possibility of modelling moving
  2D structures such as eruptive prominences.

Title: Fast 2D non-LTE radiative modelling of prominences. Numerical
    methods and benchmark results
Authors: Léger, L.; Chevallier, L.; Paletou, F.
Bibcode: 2007A&A...470....1L
Altcode: 2007astro.ph..3689L
  Context: New high-resolution spectropolarimetric observations of
  solar prominences require improved radiative modelling capabilities
  in order to take into account both multi-dimensional - at least 2D -
  geometry and complex atomic models. <BR />Aims: This makes necessary
  the use of very fast numerical schemes for the resolution of 2D
  non-LTE radiative transfer problems considering freestanding and
  illuminated slabs. <BR />Methods: The implementation of Gauss-Seidel
  and successive over-relaxation iterative schemes in 2D, together with a
  multi-grid algorithm, is thoroughly described in the frame of the short
  characteristics method for the computation of the formal solution of
  the radiative transfer equation in cartesian geometry. <BR />Results:
  We propose a new test for multidimensional radiative transfer codes
  and we also provide original benchmark results for simple 2D multilevel
  atom cases which should be helpful for the further development of such
  radiative transfer codes, in general.

Title: Differential speckle interferometry: in-depth analysis of
    the solar photosphere
Authors: Grec, C.; Aime, C.; Faurobert, M.; Ricort, G.; Paletou, F.
Bibcode: 2007A&A...463.1125G
Altcode:
  Aims:We present the results of an experiment performed at the solar
  telescope THEMIS in 2002 to measure the depth over which the solar
  granulation extends in the photosphere. <BR />Methods: Observations
  made in the 523.3 nm and 557.6 nm photospheric non-magnetic iron lines
  were correlated with images in the continuum using spectrograms. The
  difference in depth between the different levels in the photosphere
  is projected into a difference of position along the slit of the
  spectrograph, using a perspective effect similar to the well-known
  Wilson effect for sunspots. This requires measuring displacements,
  ones much smaller than the telescope resolution. This is made
  possible by using a differential speckle interferometric technique,
  cross-correlating images taken in the continuum and the line. The
  method is not adapted to following displacements of structures in
  the core of strong lines, due to their difference in shapes with
  the structures observed in the continuum. In this case, a sequential
  cross-spectrum method is developed to cross-correlate images taken
  at close wavelengths. <BR />Results: The raw results are surprising:
  displacements measured in the blue and the red wings of a line have
  opposite signs! North and South observations, however, clearly show
  the expected behavior attributed to a perspective effect. After
  a description of the observations, we give a first interpretation
  of the results. The main part of the observed displacement comes
  from the effect of unresolved Doppler shifts produced by horizontal
  velocities in the solar photosphere. The perspective effect we seek
  appears as a second-order term; we find that its amplitude is 2 or
  3 times larger than predicted by theoretical 1D models. In the core
  of strong lines we detect a contrast inversion that also shows up in
  the cross-correlation function as an anti-correlation peak at line
  center. <BR />Conclusions: .This first use of the differential speckle
  interferometry technique on the Sun is quite promising for 3D studies
  at high spatial resolution. Further observations with very good image
  quality are needed to take advantage of this new technique. <P />THEMIS
  is operated on the Island of Tenerife by CNRS-CNR in the Spanish
  Observatorio del Teide of the Instituto de Astrofísica de Canarias.

Title: Fast multilevel radiative transfer
Authors: Paletou, Frédéric; Léger, Ludovick
Bibcode: 2007JQSRT.103...57P
Altcode: 2005astro.ph..7021P
  The vast majority of recent advances in the field of numerical radiative
  transfer relies on approximate operator methods better known in
  astrophysics as Accelerated Lambda-Iteration (ALI). A superior class of
  iterative schemes, in term of rates of convergence, such as Gauss-Seidel
  and Successive Overrelaxation methods were therefore quite naturally
  introduced in the field of radiative transfer by Trujillo Bueno &amp;
  Fabiani Bendicho (1995); it was thoroughly described for the non-LTE
  two-level atom case. We describe hereafter in details how such methods
  can be generalized when dealing with non-LTE unpolarised radiation
  transfer with multilevel atomic models, in monodimensional geometry.

Title: Contrast inversion in the 557.6 nm line detected with
    differential speckle interferometry
Authors: Grec, C.; Aime, C.; Faurobert, M.; Ricort, G.; Paletou, F.
Bibcode: 2007MmSAI..78...48G
Altcode:
  We report on some aspects of the use of a Differential speckle
  interferometry technique on the Sun. The method consists in
  cross-correlating images of the granulation taken in the line
  absorption and in the continuum, outside the solar disk center. Due
  to a perspective effect, the difference in depth between different
  photospheric levels results in a difference in position along the
  spectrograph slit. Observations were done in 2002, 2005 and 2006, at
  the telescope THEMIS in the 557.6 nm iron line. As expected from the
  perspective effect, we obtain opposite results at opposite latitudes
  on the Sun disk. Surprisingly, the displacements measured in the blue
  and the red wings of the line have opposite signs. This may be the
  result of unresolved Doppler shifts produced by horizontal granular
  velocity fields. We also detect an anti-correlation peak in the core
  of strong lines, that is the signature of a contrast inversion.

Title: A Spectro-Polarimetric Survey of the Coolest Magnetic Ap Stars
Authors: Johnson, N.; Wade, G. A.; Allen, A.; Folsom, C.; Welland,
   M.; Aurière, M.; Donati, J. -F.; Jeffers, S.; Lignires, F.; Marsden,
   S.; Mouillet, D.; Paletou, F.; Petit, P.; Toqué, N.; Bagnulo, S.;
   Landstreet, J. D.; Lüftinger, T.; Ryabchikova, T.
Bibcode: 2006ASPC..358..393J
Altcode:
  This article describes the first results of a systematic
  spectro-polarimetric survey of the coolest magnetic Ap stars, undertaken
  with the MuSiCoS spectro-polarimeter, with the aim of clarifying the
  magnetic field and atmospheric characteristics of these enigmatic
  objects.

Title: The surprising magnetic topology of τ Sco: fossil remnant
    or dynamo output?
Authors: Donati, J. -F.; Howarth, I. D.; Jardine, M. M.; Petit, P.;
   Catala, C.; Landstreet, J. D.; Bouret, J. -C.; Alecian, E.; Barnes,
   J. R.; Forveille, T.; Paletou, F.; Manset, N.
Bibcode: 2006MNRAS.370..629D
Altcode: 2006MNRAS.tmp..680D; 2006astro.ph..6156D
  We report the discovery of a medium-strength (~0.5 kG) magnetic
  field on the young, massive star τ Sco (B0.2V), which becomes
  the third-hottest magnetic star known. Circularly polarized Zeeman
  signatures are clearly detected in observations collected mostly
  with the ESPaDOnS spectropolarimeter, recently installed on the 3.6-m
  Canada-France-Hawaii Telescope; temporal variability is also clearly
  established in the polarimetry, and can be unambiguously attributed
  to rotational modulation with a period close to 41 d. Archival
  ultraviolet (UV) spectra confirm that this modulation repeats over
  time-scales of decades, and refine the rotation period to 41.033
  +/- 0.002 d. <P />Despite the slow rotation rate of τ Sco, we none
  the less succeed in reconstructing the large-scale structure of its
  magnetic topology. We find that the magnetic structure is unusually
  complex for a hot star, with significant power in spherical-harmonic
  modes of degree up to 5. The surface topology is dominated by a
  potential field, although a moderate toroidal component is probably
  present. We fail to detect intrinsic temporal variability of the
  magnetic structure over the 1.5-yr period of our spectropolarimetric
  observations (in agreement with the stable temporal variations of the
  UV spectra), and infer that any differential surface rotation must be
  very small. <P />The topology of the extended magnetic field that we
  derive from the photospheric magnetic maps is also more complex than
  a global dipole, and features in particular a significantly warped
  torus of closed magnetic loops encircling the star (tilted at about
  90° to the rotation axis), with additional, smaller, networks of
  closed-field lines. This topology appears to be consistent with
  the exceptional X-ray properties of τ Sco and also provides a
  natural explanation of the variability observed in wind-formed UV
  lines. Although we cannot completely rule out the possibility that
  the field is produced through dynamo processes of an exotic kind, we
  conclude that its magnetic field is most probably a fossil remnant
  from the star formation stage. <P />Based on observations obtained
  at the Canada-France-Hawaii Telescope (CFHT) which is operated by the
  National Research Council of Canada, the Institut National des Science
  de l'Univers of the Centre National de la Recherche Scientifique of
  France, and the University of Hawaii. <P />E-mail: donati@ast.obs-mip.fr
  (J-FD); idh@star.ucl.ac.uk (IDH); mmj@st-andrews.ac.uk (MMJ);
  petit@ast.obs-mip.fr (PP); claude.catala@obspm.fr (CC); jlandstr@uwo.ca
  (JDL); jean-claude.bouret@oamp.fr (J-CB); evelyne.alecian@obspm.fr
  (EA); jrb3@st-andrews.ac.uk (JRB); forveill@cfht.hawaii.edu (TF);
  fpaletou@ast.obs-mip.fr (FP); manset@cfht.hawaii.edu (NM)

Title: A search for magnetic fields in the variable HgMn star α
    Andromedae
Authors: Wade, G. A.; Aurière, M.; Bagnulo, S.; Donati, J. -F.;
   Johnson, N.; Landstreet, J. D.; Lignières, F.; Marsden, S.; Monin,
   D.; Mouillet, D.; Paletou, F.; Petit, P.; Toqué, N.; Alecian, E.;
   Folsom, C.
Bibcode: 2006A&A...451..293W
Altcode: 2006astro.ph..1616W
  Context: .The chemically peculiar HgMn stars are a class of Bp
  stars which have historically been found to be both non-magnetic
  and non-variable. Remarkably, it has recently been demonstrated that
  the bright, well-studied HgMn star α And exhibits clear Hg ii line
  profile variations indicative of a non-uniform surface distribution
  of this element.<BR /> Aims: .With this work, we have conducted an
  extensive search for magnetic fields in the photosphere of α And.<BR />
  Methods: .We have acquired new circular polarisation spectra with the
  MuSiCoS and ESPaDOnS spectropolarimeters. We have also obtained FORS1
  circular polarisation spectra from the ESO Archive, and considered all
  previously published magnetic data. This extensive dataset has been
  used to systematically test for the presence of magnetic fields in
  the photosphere of α And. We have also examined the high-resolution
  spectra for line profile variability.<BR /> Results: .The polarimetric
  and magnetic data provide no convincing evidence for photospheric
  magnetic fields. The highest-S/N phase- and velocity-resolved Stokes V
  profiles, obtained with ESPaDOnS, allow us to place a 3σ upper limit
  of about 100 G on the possible presence of any undetected pure dipolar,
  quadrupolar or octupolar surface magnetic fields (and just 50 G for
  fields with significant obliquity). We also consider and dismiss
  the possible existence of more complex fossil and dynamo-generated
  fields, and discuss the implications of these results for explaining
  the non-uniform surface distribution of Hg. The very high-quality
  ESPaDOnS spectra have allowed us to confidently detect variability
  of Hg ii λ 6149, λ 5425 and λ 5677. The profile variability of
  the Hg ii lines is strong, and similar to that of the Hg ii λ 3984
  line. On the other hand, variability of other lines (e.g. Mn, Fe)
  is much weaker, and appears to be attributable to orbital modulation,
  continuum normalisation differences and weak, variable fringing.<BR />

Title: Direct detection of a magnetic field in the innermost regions
    of an accretion disk
Authors: Donati, Jean-François; Paletou, Fréderic; Bouvier, Jérome;
   Ferreira, Jonathan
Bibcode: 2005Natur.438..466D
Altcode: 2005astro.ph.11695D
  Models predict that magnetic fields play a crucial role in the physics
  of astrophysical accretion disks and their associated winds and
  jets. For example, the rotation of the disk twists around the rotation
  axis the initially vertical magnetic field, which responds by slowing
  down the plasma in the disk and by causing it to fall towards the
  central star. The magnetic energy flux produced in this process points
  away from the disk, pushing the surface plasma outwards, leading to a
  wind from the disk and sometimes a collimated jet. But these predictions
  have hitherto not been supported by observations. Here we report the
  direct detection of the magnetic field in the core of the protostellar
  accretion disk FU Orionis. The surface field reaches strengths of about
  1kG close to the centre of the disk, and it includes a significant
  azimuthal component, in good agreement with recent models. But we
  find that the field is very filamentary and slows down the disk plasma
  much more than models predict, which may explain why FU Ori fails to
  collimate its wind into a jet.

Title: Large-scale magnetic field of the G8 dwarf ξ Bootis A
Authors: Petit, P.; Donati, J. -F.; Aurière, M.; Landstreet, J. D.;
   Lignières, F.; Marsden, S.; Mouillet, D.; Paletou, F.; Toqué, N.;
   Wade, G. A.
Bibcode: 2005MNRAS.361..837P
Altcode: 2005MNRAS.tmp..591P; 2005astro.ph..5438P
  We investigate the magnetic geometry of the active G8 dwarf ξ Bootis
  A (ξ Boo A), from spectropolarimetric observations obtained in 2003
  with the MuSiCoS échelle spectropolarimeter at the Télescope Bernard
  Lyot (Observatoire du Pic du Midi, France). We repeatedly detect a
  photospheric magnetic field, with periodic variations consistent with
  rotational modulation. Circularly polarized (Stokes V) line profiles
  present a systematic asymmetry, showing up as an excess in amplitude
  and area of the blue lobe of the profiles. Direct modelling of Stokes
  V profiles suggests that the global magnetic field is composed of two
  main components, with an inclined dipole and a large-scale toroidal
  field. We derive a dipole intensity of about 40 G, with an inclination
  of 35° of the dipole with respect to the rotation axis. The toroidal
  field strength is of the order of 120 G. A noticeable evolution of the
  field geometry is observed over the 40 nights of our observation window
  and results in an increase in field strength and dipole inclination. <P
  />This study is the first step of a long-term monitoring of ξ Boo A
  and other active solar-type stars, with the aim of investigating secular
  fluctuations of stellar magnetic geometries induced by activity cycles.

Title: Full Stokes Spectropolarimetry of Hα in Prominences
Authors: López Ariste, A.; Casini, R.; Paletou, F.; Tomczyk, S.;
   Lites, B. W.; Semel, M.; Landi Degl'Innocenti, E.; Trujillo Bueno,
   J.; Balasubramaniam, K. S.
Bibcode: 2005ApJ...621L.145L
Altcode:
  We report on spectropolarimetric observations of Hα in prominences
  made with the Télescope Héliographique pour l'Etude du Magnétisme et
  des Instabilités Solaires and the High Altitude Observatory/Advanced
  Stokes Polarimeter. Stokes Q and U show the expected profile shape from
  resonance scattering polarization and the Hanle effect. In contrast,
  most of the time, Stokes V does not show the antisymmetric profile shape
  typical of the Zeeman effect but a profile that indicates the presence
  of strong atomic orientation in the hydrogen levels, to an extent that
  cannot be explained by invoking the alignment-to-orientation transfer
  mechanism induced by the prominence magnetic field. We found that the
  largest signal amplitudes of Stokes V (comparable to that of Stokes
  Q and U) could be produced by a process of selective absorption of
  circularly polarized radiation from the photosphere, which requires
  that the prominence be in the vicinity of an active region. Although
  recent observations of active region filaments indicate such a
  selective absorption mechanism as a plausible explanation of the
  anomalous signals observed, the particular set of conditions that
  must be met suggest that a different explanation may be required
  to explain the almost ubiquitous symmetric V signal observed in Hα
  prominences. Therefore, we speculate that an alternative mechanism
  inducing strong atomic orientation at the observed level could be due
  to the presence of electric fields inducing an electric Hanle effect
  on Hα. Although we are still working toward a careful modeling of
  this effect, including both electric and magnetic fields, we present
  some preliminary considerations that seem to support this possibility.

Title: Near Infrared Spectropolarimetry from Dome C
Authors: Donati, J. -F.; Collier Cameron, A.; Bouvier, J.; Dougados,
   C.; Ménard, F.; Catala, C.; Petit, P.; Paletou, F.; Pello, R.;
   Contini, T.; Harries, T.
Bibcode: 2005EAS....14..115D
Altcode:
  We discuss in this paper the new science perspectives that a near
  infrared (NIR) spectropolarimeter installed on a 4m class telescope
  at Dome C in Antartica would offer to the astrophysics community
  worldwide, in very diverse research fields such as stellar formation,
  extra solar planets, stellar magnetism and activity, asteroseismology,
  circumstellar environments, interstellar medium, galactic and
  extragalactic physics. We also propose an instrument concept with
  estimated performances, as well as an example 2-step scenario for the
  construction of this instrument.

Title: Dome C astronomy and astrophysics meeting
Authors: Giard, Martin; Casoli, Fabienne; Paletou, Frederic
Bibcode: 2005EAS....14.....G
Altcode:
  No abstract at ADS

Title: Rotational periods of four roAp stars
Authors: Ryabchikova, T.; Wade, G. A.; Aurière, M.; Bagnulo, S.;
   Donati, J. -F.; Jeffers, S. V.; Johnson, N.; Landstreet, J. D.;
   Lignières, F.; Lueftinger, T.; Marsden, S.; Mouillet, D.; Paletou,
   F.; Petit, P.; Reegen, P.; Silvester, J.; Strasser, S.; Toque, N.
Bibcode: 2005A&A...429L..55R
Altcode:
  Forty-five new measurements of the mean longitudinal magnetic fields
  and mean equivalent widths of 4 roAp stars have obtained using the
  MuSiCoS spectropolarimeter at Pic du Midi observatory. These new
  high-precision data have been combined with archival measurements
  in order to constrain the rotational periods of HD 12098, HD 24712
  = HR 1217, HD 122970 and HD 176232 = 10 Aql. We report a revised
  rotational period for HD 24712 (P<SUB>rot</SUB> = 12.45877 ±
  0.00016 d, crucial for interpretation of upcoming MOST observations
  of this star), new rotational periods for HD 12098 and HD 122970
  (P<SUB>rot</SUB>=5.460 ± 0.001 d and P<SUB>rot</SUB>=3.877 ± 0.001
  d, respectively) and evidence for an extremely long period for HD
  176232. <P />Table 1 is only available in electonic form at the CDS
  via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http:
  / / cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/429/L55

Title: A spectropolarimetric survey of the coolest magnetic Ap stars
Authors: Johnson, N.; Wade, G. A.; Aurière, M.; Donati, J. -F.;
   Lignires, F.; Marsden, S.; Mouillet, D.; Paletou, F.; Toqué, N.;
   Petit, P.; Bagnulo, S.; Landstreet, J. D.; Lüftinger, T.
Bibcode: 2004IAUS..224..599J
Altcode:
  We describe the first results of a systematic spectropolarimetric
  survey of the coolest magnetic Ap stars, undertaken with the MuSiCoS
  spectropolarimeter, with the aim of clarifying the magnetic field and
  atmospheric characteristics of these enigmatic objects.

Title: A survey of the weakest-field magnetic Ap stars: discovery
    of a threshold magnetic field strength?
Authors: Aurière, M.; Silvester, J.; Wade, G. A.; Bagnulo, S.; Donati,
   J. -F.; Johnson, N.; Lignières, F.; Landstreet, J. D.; Lüftinger,
   T.; Mouillet, D.; Paletou, F.; Petit, P.; Strasser, S.
Bibcode: 2004IAUS..224..633A
Altcode:
  We are conducting a magnetic survey of a sample of about 30
  spectroscopically identified Ap stars, with weak or previously
  undetected magnetic fields. For 28 studied stars, we have obtained 25
  detections of Stokes V Zeeman signatures. Our results suggest that
  all Ap stars are magnetic. Further there may exist a minimum field
  strength for which Ap-type characteristics are produced.

Title: Exact vs. Gauss-Seidel numerical solutions of the non-LTE
    radiation transfer problem
Authors: Quang, Carine; Paletou, Frédéric; Chevallier, Loïc
Bibcode: 2004sf2a.conf..317Q
Altcode: 2006astro.ph..1462Q; 2004sf2a.confE.322Q
  Although published in 1995 (Trujillo Bueno &amp; Fabiani Bendicho, ApJ
  455, 646), the Gauss-Seidel method for solving the non-LTE radiative
  transfer problem has deserved too little attention in the astrophysical
  community yet. Further tests of the performances and of the accuracy
  of the numerical scheme are provided.

Title: A survey of Ap stars for weak longitudinal magnetic fields
Authors: Auriere, M.; Silvester, J.; Wade, G. A.; Bagnulo, S.; Donati,
   J. F.; Johnson, N.; Landstreet, J. D.; Lignieres, F.; Lueftinger,
   T.; Mouillet, M.; Paletou, F.; Petit, P.; Strasser, S.
Bibcode: 2004mast.conf..114A
Altcode:
  We are conducting a magnetic survey of a sample of about 30
  spectroscopically-identified Ap stars (selected from the HD catalogue),
  but with faint or previously undetected magnetic fields. We use the
  MuSiCoS spectropolarimeter at Telescope Bernard Lyot (Pic du Midi
  Observatory, France) and the cross-correlation technique Least Squares
  Deconvolution (LSD; Donati et al. 1997). For 24 studied stars, we have
  obtained 21 detections of Stokes V Zeeman signatures (data quality
  and phase coverage may explain our lack of detection of any field in
  some objects). Our results suggest that all Ap stars are magnetic and,
  furthermore, that there may exist a minimum field strength for which
  Ap-type characteristics are produced.

Title: No weak magnetic field detected in the variable HgMn star
    α Andromedae
Authors: Wade, G. A.; Abecassis, M.; Auriere, M.; Donati, J. -F.;
   Ligneres, F.; Marsden, S.; Mouillet, D.; Paletou, F.; Petit, P.;
   Toque, N.; Monin, D.; Landstreet, J. D.; Bagnulo, S.; Luftinger, T.
Bibcode: 2004mast.conf..108W
Altcode:
  High-S/N, phase-distributed circular polarisation spectra of the
  variable HgMn star α And provide no evidence of any photospheric
  magnetic field, with an upper limit for oblique dipolar fields of 280
  G (approximately the equipartition field at log τ<SUB>5000</SUB> =
  0.0). We therefore propose that the variability of the Hg λ3984 line
  and the inferred nonuniform distribution of Hg (reported by Adelman et
  al. 2002) most plausibly result from a separation mechanism unrelated
  to the presence of a magnetic field.

Title: Photospheric magnetic field and surface differential rotation
    of the FK Com star HD 199178
Authors: Petit, P.; Donati, J. -F.; Oliveira, J. M.; Aurière, M.;
   Bagnulo, S.; Landstreet, J. D.; Lignières, F.; Lüftinger, T.;
   Marsden, S.; Mouillet, D.; Paletou, F.; Strasser, S.; Toqué, N.;
   Wade, G. A.
Bibcode: 2004MNRAS.351..826P
Altcode: 2004astro.ph..3284P
  We present spectropolarimetric observations of the FK Com star HD 199178
  obtained between 1998 December and 2003 August at the Télescope Bernard
  Lyot (Observatoire du Pic du Midi, France). We report the detection
  of a photospheric magnetic field and reconstruct its distribution by
  means of Zeeman-Doppler imaging. We observe large regions where the
  magnetic field is mainly azimuthal, suggesting that the dynamo processes
  generating the magnetic activity of HD 199178 may be active very close
  to the stellar surface. We investigate the rapid evolution of surface
  brightness and magnetic structures from a continuous monitoring of the
  star over several weeks in 2002 and 2003. We report that significant
  changes occur in the distribution of cool-spots and magnetic regions on
  typical time-scales of the order of two weeks. Our spectropolarimetric
  observations also suggest that the surface of HD 199178 is sheared
  by differential rotation, with a difference in rotation rate between
  equatorial and polar regions of the order of 1.5 times that of the Sun.

Title: Surface Differential Rotation of Evolved Fast Rotators
Authors: Petit, P.; Donati, J. -F.; MUSICOS Collaboration; Wade,
   G. A.; Landstreet, J. D.; Sigut, T. A. A.; Shorlin, S. L. S.; Bagnulo,
   S.; Lüftinger, T.; Strasser, S.; Oliveira, J. M.; Aurière, M.;
   Lignières, F.; Mouillet, D.; Paletou, F.
Bibcode: 2004IAUS..215..294P
Altcode:
  No abstract at ADS

Title: On the accuracy of the ALI method for solving the radiative
    transfer equation
Authors: Chevallier, L.; Paletou, F.; Rutily, B.
Bibcode: 2003A&A...411..221C
Altcode: 2006astro.ph..1341C
  We solve the integral equation describing the propagation of light
  in an isothermal plane-parallel atmosphere of optical thickness tau
  <SUP>*</SUP>, adopting a uniform thermalization parameter epsilon . The
  solution given by the ALI method, widely used in the field of stellar
  atmosphere modelling, is compared to the exact solution. Graphs are
  given that illustrate the accuracy of the ALI solution as a function
  of the parameters epsilon , tau <SUP>*</SUP> and optical depth variable
  tau .

Title: Escape probability methods versus ``exact" transfer for
    modelling the X-ray spectrum of Active Galactic Nuclei and X-ray
    binaries
Authors: Dumont, A. -M.; Collin, S.; Paletou, F.; Coupé, S.; Godet,
   O.; Pelat, D.
Bibcode: 2003A&A...407...13D
Altcode: 2003astro.ph..6297D
  In the era of XMM-Newton and Chandra missions, it is crucial to use
  codes able to compute correctly the line spectrum of X-ray irradiated
  thick media (Thomson thickness of the order of unity), in order
  to build models for the structure and the emission of the central
  regions of Active Galactic Nuclei (AGN), or of X-ray binaries. In all
  photoionized codes except in our code Titan, the line intensities are
  computed with the so-called ``escape probability approximation". In
  its last version, Titan solves the transfer of a thousand lines and of
  the continuum with the ``Accelerated Lambda Iteration" method, which
  is one of the most efficient and at the same time the most secure for
  line transfer. We first review the escape probability formalism and
  mention various reasons why it should lead to wrong results concerning
  the line fluxes. Then we check several approximations commonly used
  instead of line transfer in photoionization codes, by comparing them
  to the full transfer computation. We find that for conditions typical
  of the AGN or X-ray binary emission medium, all approximations lead
  to an overestimation of the emitted X-ray line spectrum, which can
  reach more than one order of magnitude. We show that it is due mainly
  to the local treatment of line photons, implying a delicate balance
  between excitations of X-ray transitions by the very intense underlying
  diffuse X-ray continuum (which are not taken properly into account in
  escape probability approximations) and the net rate of excitations
  by the diffuse line flux. The most affected lines are those in the
  soft X-ray range. Such processes are much less important in cooler and
  thinner media (like the Broad Line Region of AGN), as the most intense
  lines lie in the optical and near ultraviolet range where the diffuse
  continuum is small. We conclude that it is very important to treat
  correctly the transfer of the continuum to get the best results for the
  line spectrum. On the other hand the approximations used for the escape
  probabilities have a relatively small influence on the computed thermal
  and ionization structure of the surface layers, but in the deep layers,
  they lead to an overestimation of the ionization state. As a consequence
  the computed continuum emitted by the back (non-irradiated) side is
  not correct, and might be strongly overestimated in the EUV range.

Title: A survey of magnetic Ap/Bp stars for weak longitudinal
    magnetic fields
Authors: Auriere, M.; Silvester, J.; Wade, G. A.; Bagnulo, S.; Donati,
   J. -F.; Johnson, N.; Landstreet, J. D.; Ligneres, F.; Lueftinger,
   T.; Mouillet, D.; Paletou, F.; Petit, P.; Strasser, S.
Bibcode: 2003APN....39.....A
Altcode:
  We describe an ongoing observational programme, using the MuSiCoS
  spectropolarimeter at Pic du Midi Observatory, aimed at detecting
  the weakest magnetic fields of Ap/Bp stars. For the 21 stars
  observed up to now, we have obtained 19 detections of Stokes V Zeeman
  signatures. This remarkable detection rate strongly suggests that all
  Ap stars having "magnetic" behaviour (Preston 1974; i.e. essentially
  all stars classified spectroscopically as Ap/Bp) actually harbour
  magnetic fields. In other words, all Ap stars appear to be observably
  magnetic. <P />For some of our stars with sufficient measurements
  and suitable phase sampling, dipolar oblique rotator models have been
  determined. Although results are preliminary, we find that magnetic
  geometry or rotational phase variations can explain the apparent
  faintness of the measured fields, and that the dipole strength for this
  small sample is at least several hundred G. In other words, at present
  we find no evidence for inferred dipolar surface fields weaker than
  a few hundred G in any Ap star. As suggested by Glagolevskij &amp;
  Chountonov (2002), this result may indicate that there is a minimum
  field strength for which Ap-type characteristics are produced. This
  minimum strength appears to be of order the photospheric equipartition
  field (around 230 G for a main sequence A0 star).

Title: Spectropolarimetry of Solar Prominences
Authors: Paletou, F.; Aulanier, G.
Bibcode: 2003ASPC..307..458P
Altcode:
  No abstract at ADS

Title: On the Need of High-Resolution Spectropolarimetric Observations
    of Prominences
Authors: Paletou, F.; Aulanier, G.
Bibcode: 2003ASPC..286...45P
Altcode: 2003ctmf.conf...45P
  No abstract at ADS

Title: The accuracy of the ALI method for solving the radiative
    transfer equation in stellar atmospheres
Authors: Chevallier, L.; Paletou, F.; Rutily, B.
Bibcode: 2003sf2a.conf..581C
Altcode: 2006astro.ph..1460C; 2003sf2a.confE.240C
  We test the accuracy of the ALI method, widely used in stellar
  atmospheres modelling, by solving exactly a standard radiative transfer
  problem in plane-parallel geometry. Some recommendations are given for
  a practical use of this method in stellar atmospheres numerical codes.

Title: Caution! Modelling the X-ray spectrum of AGN and X-ray binaries
is not simple: Escape probabilities versus transfer computations
Authors: Dumont, A. -M.; Collin, S.; Paletou, F.; Coupé, S.; Godet,
   O.; Pelat, D.
Bibcode: 2003sf2a.conf..475D
Altcode: 2003sf2a.confE.203D
  We compare different escape probability approximations commonly used
  for the line transfer in photoionisation codes, with a full transfer
  computation performed with the Accelerated Lambda Iteration method
  (ALI), using our code Titan specially designed for thick hot media. For
  a case typical of the UV-X emitting region in AGN or in X-ray binaries,
  we show that the emitted line intensities in the X-ray range are
  generally overestimated by the approximation procedures, sometimes by
  up to one order of magnitude. This is a strong problem at the era of XMM
  and Chandra missions which allow observing detailed X-ray features, used
  to deduce the physical conditions of the emission/absorbing regions.

Title: The Advanced Technology Solar Telescope
Authors: Paletou, F.; López Ariste, A.; Meunier, N.; Molodij, G.
Bibcode: 2003sf2a.conf...97P
Altcode: 2003sf2a.confE..30L
  The Advanced Technology Solar Telescope (ATST) is a 4-m aperture solar
  telescope project lead by the NSO and supported by all major solar US
  research institutes. Also a European initiative gathering 17 countries,
  so far, is currently being prepared in support of the project. ATST,
  intended for first light in 2010, will provide the high-angular
  resolution required for nowadays photospheric studies; but its large
  aperture and controlled scattered-light design makes it also a very
  promising tool for high sensitivity spectropolarimetric observations
  needed throughout the whole solar atmosphere up to the corona, and in
  spectral windows ranging from the visible to the thermal infrared.

Title: Full-Stokes spectropolarimetry of solar prominences
Authors: Paletou, F.; López Ariste, A.; Bommier, V.; Semel, M.
Bibcode: 2001A&A...375L..39P
Altcode:
  We report on first spectropolarimetric observations of solar prominences
  made at THEMIS. Hereafter we shall emphasis on the preliminary analysis
  of He I D<SUB>3</SUB> full-Stokes observations. Our measurements
  clearly show manifestations of both the Hanle and Zeeman effects. More
  generally, we demonstrate the very favourable performances of the THEMIS
  multi-line spectropolarimetric mode for further new investigations of
  the magnetic field in solar prominences. Based on observations made at
  THEMIS, operated on the Island of Tenerife by CNRS-CNR in the Spanish
  Observatorio del Teide of the Instituto de Astrofísica de Canarias.

Title: THÉMIS Observations of the Second Solar Spectrum
Authors: Trujillo Bueno, J.; Collados, M.; Paletou, F.; Molodij, G.
Bibcode: 2001ASPC..236..141T
Altcode: 2001aspt.conf..141T
  No abstract at ADS

Title: Scattering Induced Polarization and Hanle Effect Observations
    with THEMIS
Authors: Arnaud, J.; Faurobert, M.; Vigneau, J.; Paletou, F.
Bibcode: 2001ASPC..248...93A
Altcode: 2001mfah.conf...93A
  No abstract at ADS

Title: Transfert de rayonnement : méthodes itératives
Authors: Paletou, F.
Bibcode: 2001CRPhy...2..885P
Altcode:
  Dans cet article, je décrirai diverses méthodes permettant de
  résoudre des problèmes de transfert de rayonnement considérant
  successivement l'atome à deux niveaux, puis les effets de
  redistribution partielle en fréquence, l'atome à plusieurs niveaux et,
  enfin, la polarisation du rayonnement. La méthode numérique dite ALI
  (pour Accelerated Lambda-Iteration) est le dénominateur commun à
  toutes ces méthodes.

Title: THEMIS Multi-Line Spectropolarimetry
Authors: Paletou, F.; Molodij, G.
Bibcode: 2001ASPC..248..617P
Altcode: 2001mfah.conf..617P
  No abstract at ADS

Title: Scattering Polarization Measurements with THÉMIS
Authors: Arnaud, J.; Vigneau, J.; Faurobert, M.; Paletou, F.
Bibcode: 2001ASPC..236..151A
Altcode: 2001aspt.conf..151A
  No abstract at ADS

Title: Multi-line Spectropolarimetry at THÉMIS
Authors: Paletou, F.; Molodij, G.
Bibcode: 2001ASPC..236....9P
Altcode: 2001aspt.conf....9P
  No abstract at ADS

Title: An Operator Perturbation Method of Polarized Line Transfer
    V. Diagnosis of Solar Weak Magnetic Fields
Authors: Nagendra, K. N.; Frisch, H.; Faurobeet-Scholl, M.; Paletou, F.
Bibcode: 2000JApA...21..255N
Altcode:
  No abstract at ADS

Title: Observations à haute sensibilité polarimétrique à THEMIS
Authors: Paletou, F.; Molodij, G.
Bibcode: 2000CRPhy...1.1309P
Altcode: 2000CRAS....1.1309P
  Une observation effectuée le 7 Avril 2000 nous a permis de mesurer
  avec une grande précision la polarisation linéaire dans la raie D2
  de NaI observée près du bord solaire. Ceci nous permet de démontrer
  le très grand potentiel de performance du télescope solaire THEMIS
  en matière de mesure de signaux de polarisation faibles.

Title: An operator perturbation method for polarized line transfer IV:
    Applications to the Hanle effect with partial frequency redistribution
Authors: Nagendra, K. N.; Paletou, F.; Frisch, H.; Faurobert-Scholl, M.
Bibcode: 1999ASSL..243..127N
Altcode: 1999sopo.conf..127N
  No abstract at ADS

Title: Polarized radiation transfer in 2D geometry
Authors: Paletou, F.; Bommier, V.; Faurobert-Scholl, M.
Bibcode: 1999ASSL..243..189P
Altcode: 1999sopo.conf..189P
  No abstract at ADS

Title: Polarized redistribution matrix for Hanle effect: Numerical
    tests
Authors: Faurobert-Scholl, M.; Paletou, F.; Bommier, V.
Bibcode: 1999ASSL..243..115F
Altcode: 1999sopo.conf..115F
  No abstract at ADS

Title: On the Bright Rims of H-alpha Filaments
Authors: Paletou, F.
Bibcode: 1998ASPC..150...70P
Altcode: 1998IAUCo.167...70P; 1998npsp.conf...70P
  No abstract at ADS

Title: An operator perturbation method for polarized line
    transfer. II. Resonance polarization with partial frequency
    redistribution effects
Authors: Paletou, Frederic; Faurobert-Scholl, Marianne
Bibcode: 1997A&A...328..343P
Altcode:
  The effects of partial frequency redistribution are implemented in the
  Polarized Accelerated Lambda Iteration (PALI) method of Faurobert-Scholl
  et al. (1997). The numerical scheme is an extension of the core-wing
  technique of Paletou &amp; Auer (1995) originally developed for
  non-polarized line transfer problems. Using a new code, we validate
  theoretical results against those given by a Feautrier type code.

Title: On Hα source function vertical variations in filaments and
    bright rims visibility.
Authors: Paletou, F.
Bibcode: 1997A&A...317..244P
Altcode:
  Using new radiative modelling capabilities in two-dimensional (2D)
  cartesian geometry, we investigate the vertical variations of the
  Hα source function in filaments. It is shown how the two-dimensional
  geometry can affect the transfer of the Hα line into filaments and,
  consequently, how assumptions on the geometry of the model may influence
  a further interpretation of observations. A special attention is paid
  to the possibility of formation of a bright rim inside the filament
  body by diffusive penetration of Hα radiation. Unlike recently
  proposed by Heinzel et al. (1995SoPh..160...19H), we can see from our
  2D computations that the observable emergent intensities are not high
  enough to explain bright rims contrasts.

Title: A note on improved computations of solar prominences: 2D
    radiative models.
Authors: Paletou, F.
Bibcode: 1996A&A...311..708P
Altcode:
  We report on improved computations concerning two-dimensional (2D)
  radiative modelling of solar prominences. This report mainly concerns
  a more correct definition of the bound-free radiative rates (incident
  radiation and dilution factor). As a consequence, the difference (at
  a given height) between the Hα line integrated intensity computed
  respectively in 1D and 2D geometries is found to be less important
  than what was previously presented (Paletou 1995).

Title: Transfert de rayonnement hors-ETL et applications en physique
    solaire.
Authors: Faurobert-Scholl, M.; Paletou, F.; Frisch, H.
Bibcode: 1996JAF....53...24F
Altcode:
  No abstract at ADS

Title: Two-dimensional multilevel radiative transfer with standard
    partial frequency redistribution in isolated solar atmospheric
    structures.
Authors: Paletou, F.
Bibcode: 1995A&A...302..587P
Altcode:
  We have implemented standard partial frequency redistribution (PRD)
  in a two-dimensional multilevel non-LTE radiative transfer code. The
  Multilevel Accelerated Lambda Iteration (MALI) method is used. First,
  a numerical approach for treating standard PRD effects is described,
  as well as a simple method for treating an optically thick bound-free
  transition with MALI. Then, the method is validated in mono-dimensional
  geometry. Finally, preliminary results from two-dimensional radiative
  modelling of solar prominences are presented.

Title: A new approximate operator method for partial frequency
    redistribution problems.
Authors: Paletou, F.; Auer, L. H.
Bibcode: 1995A&A...297..771P
Altcode:
  Methods for the solution of non-lte partial frequency redistribution
  (prd) radiative transfer problems are presented. By explicitly
  treating the partial frequency coherence, convergence difficulties
  caused by using a Complete Redistribution Approximation are completely
  overcome. A new core-wing treatment of the redistribution both avoids
  the explicit solution of the frequency coupled system, and permits
  the use of simple Approximate Operator Iteration to solve prd problems
  extremely efficiently.

Title: Two-dimensional radiative transfer with partial frequency
    redistribution I. General method
Authors: Auer, L. H.; Paletou, F.
Bibcode: 1994A&A...285..675A
Altcode:
  We present a new method for the solution of non-LTE scattering
  problems in two dimensions. It is based on Accelerated Lambda
  Iteration and an improved short characteristic method. It is more
  than an order of magnitude faster than a direct approach for Complete
  Redistribution. We, further, have extended the method to the solution of
  Partial Redistribution problems. The computational cost of treating PRD
  with the new method is only a small factor larger than CRD. Results with
  the new iterative approach are in complete agreement with previously
  published results.

Title: Two-dimensional radiative transfer with partial frequency
    redistribution. II. Application to resonance lines in quiescent
    prominences
Authors: Paletou, F.; Vial, J. -C.; Auer, L. H.
Bibcode: 1993A&A...274..571P
Altcode:
  Theoretical emergent profiles in the resonance lines of H I Lyman α,
  Mg II h &amp; k and Ca II H &amp; K formed in quiescent prominences
  are presented. Both partial frequency redistribution effects and
  two-dimensional structure have been included in the calculations. The
  prominence model consists of a static, isobaric and isothermal
  freestanding slab irradiated by realistic chromospheric profiles
  (080-8 observations). We compare the differences between complete (CRD)
  and partial frequency redistribution (PRD). Vertical variations in the
  emergent profiles are displayed, and the importance of the geometrical
  effects is discussed. In addition, we have evaluated both emergent
  profiles for a filament as seen over the disk, and the back-scattered
  radiation towards the chromosphere.

Title: Radiative modeling of solar prominences, two-dimensional
    transfer plus partial frequency redistribution.
Authors: Paletou, F.; Vial, Jean-Claude; Auer, L. H.
Bibcode: 1992ESASP.348..225P
Altcode: 1992cscl.work..225P
  The two-dimensional, PRD radiative transfer code of Auer and
  Paletou (1992) has been used to compute the resonance lines of H
  I, Mg II and Ca II in quiescent prominences, which are modeled as
  isothermal freestanding slabs illuminated from the sides as well as
  from below. Partial redistribution (PRD) and 2D effects are evidenced
  and compared to complete redistribution computations for both 1D and
  2D geometries. Important edge variations are fround at the bottom
  and the top that should be observed with a spatial resolution of one
  arcsecond. As in 1D, PRD effects allow for greater penetration of the
  incident radiation into the layer. The 2D code computes both the radial
  emergent intensity and the amount of radiation backscattered into the
  chromosphere. It can, accordingly, be used to estimate the visibility of
  filaments. It will be of special interest to build non-isothermal models
  and compare e.g. the Lyα profiles with the SUMER/SOHO observations.

