Author name code: mehltretter
ADS astronomy entries on 2022-09-14
author:"Mehltretter, J.P." 
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Title: Alignment tolerances of the proposed Ritchey-Chretien system,
    and interferometric control of its alignment
Authors: Mehltretter, J. P.
Bibcode: 1982STIN...8232225M
Altcode:
  Numerical data on LEST alignment tolerances (deformation constants,
  inclination of primary mirror axis with respect to system axis,
  inclination of secondary mirror axis, lateral and axial shift of
  secondary) are given. The alignment system has to provide both
  inclination and lateral shift of the secondary with respect to the
  primary and its axis. Tolerances are such, e.g., 15 microns lateral
  shift, that passive systems cannot assure alignment. A system which
  places four interferometers in the primary and secondary mirror holes,
  and uses a zero order white fringe for displacement and tilt detection
  is proposed. An inclination of the primary can be treated as a lateral
  shift and tilt of the secondary.

Title: Reimaging systems for use with the proposed Ritchey-Chretien
    main telescope
Authors: Mehltretter, J. P.
Bibcode: 1982lest.rept..240M
Altcode:
  A convex-concave Cassegrain system, and an apochromatic triplet lens
  system (S-shaped color curve) are discussed for the large European
  solar telescope secondary magnification set up. A magnification ratio
  between 7 and 10 of the F7 primary focal plane is required. The second
  focus is placed below the coelostat, and the total length between
  the primary focus and the coelostat entrance is 300 mm. Although the
  quasi-Cassegrain and triplet lens systems are theoretically feasible,
  practical implementation is extremely difficult because of alignment
  problems arising from narrow tolerances. An increase of the focal
  ratio of the primary focus, to, e.g., F15, and increasing the space
  between the main telescope and coelostat are suggested.

Title: On some quasi-concentric optical systems for the Large-European
    Solar Telescope (LEST)
Authors: Mehltretter, J. P.
Bibcode: 1982lest.rept..209M
Altcode:
  The large European solar telescope specifications (2.5 m aperture, no
  image rotation in the final focal plane, minimum of optical surfaces
  and instrument polarization) are discussed, and the merits of various
  systems (coaxial, skewed) are compared. A positive skew array of two
  mirrors (Schiefspiegler system) is ruled out because the highly inclined
  focal planes mean that the useful field is too small, and considerable
  focusing is required. Compact Cassegrain or Gregory systems in front
  of a coelostat system also have field of view limitations. Heliostat
  systems, using a single long focus primary mirror are advocated.

Title: Vacuum and window with rim and center support
Authors: Mehltretter, J. P.
Bibcode: 1982lest.rept..205M
Altcode:
  Expressions for the bending stresses of a telescope window with a
  small additionally supported central area are presented. Expressions
  for maximum bending elongation are taken from the literature, and
  those for radial and tangential stresses are deduced from the bending
  moments for given distances from the plate center. Analysis shows
  that where the central bending excursion is zero, very high stresses
  equal to those in a window which is not centrally supported occur
  at the central support. Overall stress can be reduced by choosing
  the support pressure inside the central area so that radial stress
  vanishes at the outer boundary of the central support. Along the rim,
  a hydraulic support system consisting of two concentric O-shaped rings
  is suggested. For the central support, a frictionless hydraulic piston
  and an O-ring sealed support plate are advocated.

Title: Window for vacuum telescopes: Review of problem areas
Authors: Mehltretter, J. P.
Bibcode: 1982lest.rept..199M
Altcode:
  The mechanical properties of a large disk of BK7 glass, and the
  optical effects of the pressure load and thermal environment are
  discussed. A 150 cm diameter free window is feasible using BK7. For a
  maximum bending stress not exceeding 125 kp/sq cm, thickness should
  be greater than 7.7 cm. Active temperature control of the cell is
  required to overcome thermal nonuniformities between center and rim
  and to eliminate birefringence due to thermally induced stress. If
  multiwindow apertures are used, temperature within the assembly must
  be constant within 0.1K in the coherent case. The wedge angle of
  the elements should equal twice the resolution angle for incoherent
  use. The thickness should equal 0.2 lambda, the amount corresponding
  to a constant wedge angle for a coherent case window.

Title: Granular-size horizontal velocities in the solar atmosphere
Authors: Mattig, W.; Mehltretter, J. P.; Nesis, A.
Bibcode: 1981A&A....96...96M
Altcode:
  Observations of horizontal motions in the granulation of the solar
  photosphere and the center-to-limb variations are reported. Measurements
  of the Fe I 5121.649, Cr I 5122.121 and Fe I 5123.730 lines were
  obtained by the balloon-borne spectro-stratoscope with slit direction
  tangential to the limb. Following correction for known instrumental
  effects, rms line velocities are found to increase towards the limb,
  and to contain a horizontal component approximately twice as large as
  the vertical component. The results are noted to be in agreement with
  those of Keil and Canfield (1978) at lower photospheric heights, and
  those of Beckers and Canfield (1975) at greater photospheric heights.

Title: On the proper motions of small pores in sunspot groups.
Authors: Mehltretter, J. P.
Bibcode: 1979SoPh...63...61M
Altcode:
  The possibility of measuring pore positions and proper motions with
  high accuracy, using time series of short exposure photographs,
  is discussed. Preliminary measurements of a series covering a time
  span of 110 min. show that positions of small pores may be defined,
  and horizontal velocities determined, to within 0″.1, or 30 m
  s<SUP>−1</SUP>, respectively.

Title: On the center to limb variation of the granular brightness
    fluctuations.
Authors: Schmidt, W.; Deubner, F. -L.; Mattig, W.; Mehltretter, J. P.
Bibcode: 1979A&A....75..223S
Altcode:
  The center to limb variation of the granular brightness contrast
  was studied on the basis of slit-jaw photographs obtained with the
  balloon-borne Spektro-Stratoskop telescope, flown at an altitude of
  about 28 km on May 17, 1975 and during the partial solar eclipse of
  April 26, 1976 on Tenerife. Positions concentrate at cosine theta
  values of about 1, 0.6 and 0.2. The granular contrast was found to
  decrease monotonically towards the solar limb, with the magnitude of
  contrast about three times smaller at cosine theta 2 than at the disk
  center. The relative center to limb variation was found to be 10.4%
  (eclipse observations by a 40 cm evacuated Newtonian reflector at 422
  nm) and 8.6% (Spektro-Stratoskop observations at 556 nm). Discrepancies
  between these results and those reported by Deubner and Mattig (1975)
  are thought to be due to corrections for photographic noise and other
  factors.

Title: On thermal-optical distortions of glass disks.
Authors: Mehltretter, J. P.
Bibcode: 1979JOpt...10...93M
Altcode: 1979JOp....10...93M
  A simple model of the thermal equilibrium conditions in a glass disk
  is developed as an aid to designing a cooling system for the vacuum
  entrance window of a telescope. Optical deformations due to uneven
  temperature distributions across glass disks include defocussing,
  spherical aberration and astigmatism. Analyses of these optical
  deformations are applied to the case of the objective lens of a 50-cm
  aperture solar refractor. Addition of a shade to the lens cell improved
  the optical performance of the refractor.

Title: Solar optical telescope (SOT).
Authors: Dunn, R. B.; Fisher, R.; Harvey, J.; Lemaire, P.; Milkey,
   R.; Smithson, R.; Beckers, J.; Mehltretter, J. P.; Zirin, H.
Bibcode: 1979MmArc.106..135D
Altcode:
  No abstract at ADS

Title: Science opportunities with the SOT.
Authors: Dunn, R. B.; Fisher, R.; Harvey, J.; Lemaire, P.; Milkey,
   R.; Smithson, R.; Beckers, J.; Mehltretter, J. P.; Zirin, H.
Bibcode: 1979MmArc.106..245D
Altcode:
  No abstract at ADS

Title: Die Mitte-Rand-Variation des granularen Intensitätskontrastes
Authors: Schmidt, W.; Deubner, F. L.; Mattig, W.; Mehltretter, J. P.
Bibcode: 1979MitAG..45..148S
Altcode:
  No abstract at ADS

Title: Project Spectrostratoscope: Balloon-borne solar research
Authors: Mehltretter, J. P.; Mattig, W.; Vonalvensleben, A.
Bibcode: 1978fifg.rept.....M
Altcode:
  A historical review of the project development (1961 to 1975) is
  followed by an outline description of the instrument. More details
  on the technical problems related to photometry and the quantitative
  analysis of the observations are then given. Focusing, instrument
  profile, instrumental polarization, pointing, and guiding stability
  are discussed. After a brief description of the balloon flight of
  17 May 1975, The functioning of critical components and the thermal
  behavior of the instrument are analyzed. The scientific program for
  the investigation of photospheric granulation by means of time series
  integrated light pictures and spectra with high angular and spectral
  resolutin is described; first results concerning life times temperature
  fluctuations, and velocities of granules are reported.

Title: Was wissen wir von der Granulation?
Authors: Mehltretter, J. P.
Bibcode: 1978S&W....17..207M
Altcode:
  Initial problems concerning the study of solar granulation are
  related to phenomena produced in photographs of granulation by the
  disturbed optical characteristics of the terrestrial atmosphere
  (seeing). The interest in granulation investigations increased
  significantly in the 1950's in connection with developments in
  theoretical astrophysics. Unsoeld (1930) had shown that the convection
  in the interior of the sun plays a decisive part at the temperatures
  at which hydrogen is ionized, corresponding to areas just below the
  solar 'surface'. He pointed out the relation between granulation and
  convection. At about 1950, the theory of turbulent processes had reached
  a level at which questions were asked concerning the size distribution
  and the temperature differences found in granulation. Ground-based
  and balloon-based observations introduced at this time the era of
  modern granulation observations. Attention is given to the granulation
  phenomenon, the physical processes involved, and the possibilities
  to obtain information regarding the characteristic parameters of the
  convection zone on the basis of granulation studies.

Title: Balloon-borne imagery of the solar granulation. II. The
    lifetime of solar granulation.
Authors: Mehltretter, J. P.
Bibcode: 1978A&A....62..311M
Altcode:
  Phenomenological aspects of the temporal evolution of photospheric
  granulation are reported as derived from time series of granulation
  photographs obtained during a flight of a balloon-borne telescope. The
  distribution of granule lifetime probabilities is determined,
  and it is found that the data can be represented by an exponential
  decrease with a 'decay constant' of 5.9 min. The general properties
  of granular evolution are described along with the way individual
  granules evolve with time. The most common type of granule is shown
  to be a medium-sized or small fragment, and it is suggested that all
  granules are produced by fragmentation of preexisting granules. The
  relative frequencies of granule destruction by fragmentation, fading,
  and merging are determined to be 51%, 21%, and 28%, respectively. An
  average radial velocity of 0.8 km/s is computed for conglomerates with
  an average diameter of 2.25 arcsec.

Title: Sonnenfackeln und "Filigree".
Authors: Mehltretter, J. P.
Bibcode: 1978S&W....17..364M
Altcode:
  No abstract at ADS

Title: Balloon-borne imagery of the solar granulation. I. Digital
    image enhancement and photometric properties.
Authors: Wittmann, A.; Mehltretter, J. P.
Bibcode: 1977A&A....61...75W
Altcode:
  Summary. Digital image processing and restoration techniques have been
  applied to high-resolution photographs of the solar granulation that
  were obtained with a balloon-borne telescope. The final resolution that
  has been achieved is 0.3" or 220 km on the sun. From the digitized and
  computer-processed images we have determined photometric properties
  of the solar granulation at the disc centre: The true rms amplitude
  ofthe granular intensity fluctuation is found to be 8.7 %, which for a
  simplified model of bright and dark elements corresponds to a contrast
  of 19.0 %. At 5560 A this is equivalent to a blackbody temperature
  difference of 254 K. The fractional area occupied by elements darker
  than average is 52.4 %. Key words: solar granulation image processing

Title: Über die Lebensdauer der photosphärischen Granulation
Authors: Mehltretter, J. P.
Bibcode: 1977MitAG..42..113M
Altcode:
  No abstract at ADS

Title: Computer-Processed Granulation Pictures of Project
    "Spectro-Stratoscope"
Authors: Wittmann, A.; Mehltretter, J. P.
Bibcode: 1977MitAG..42..114W
Altcode:
  The pictures which were processed had been obtained on May 17, 1975,
  when a balloon-borne solar telescope performed a 10-hour flight at 27
  km altitude. During the flight 400 spectrograms and 1000 high-quality
  white light pictures were obtained of the solar granulation. Digital
  image enhancement and restoration techniques were afterwards applied
  to the digitized, two-dimensional intensity distribution. The employed
  deconvolution method, which is known as van Cittert's method, has been
  described by van Wittmann (1971). The final resolution achieved is
  approximately 110 km on the solar surface. According to the obtained
  results the granules are approximately 1.19 times as bright as the
  intergranular background.

Title: Der Flug von Spektro-Stratoskop.
Authors: Mehltretter, J. P.
Bibcode: 1976S&W....15...44M
Altcode:
  The paper gives a general description of the Spektro-Stratoskop,
  a balloon-borne solar spectrometer which in May 1975 successfully
  performed a series of observations from the stratosphere on the
  evolution of solar granulation, bringing back to earth time-lapse
  photographs of granulation on various parts of the solar disk. At
  present, some qualitative results have been obtained from the data. It
  has been determined that neither wave phenomena nor stationary
  convection cells are involved in granulation. Most of the granulation
  elements develop in an 'explosive-like' manner: an at first rather
  insignificant small granule becomes brighter, expands (occasionally in
  the shape of a ring), and finally breaks up into smaller fragments,
  which either disappear or repeat the process, which lasts from 10 to
  20 minutes.

Title: Die zeitliche Entwicklung der Granulation
Authors: Mehltretter, J. P.
Bibcode: 1976MitAG..40R.162M
Altcode:
  No abstract at ADS

Title: Der Flug von Spektro-Stratoskop.
Authors: Mehltretter, J. P.
Bibcode: 1976MitAG..38..137M
Altcode:
  No abstract at ADS

Title: Solar activity (Activité solaire).
Authors: Newkirk, G.; Dunn, R. B.; Mehltretter, P.; MacQueen, R.;
   Bonnet, R. M.; White, O. R.; Fokker, A. D.; Zwaan, C.; Bruzek, A.;
   Durrant, C.; Grossmann-Doerth, U.; Mehltretter, J. P.; Svestka, Z.;
   de Feiter, L. D.; Tandberg-Hanssen, E.; Howard, R.; Stix, M.; Pneuman,
   G. W.; Hundhausen, A. J.; Sawyer, C.; Simon, P.
Bibcode: 1976IAUTA..16b..13N
Altcode:
  No abstract at ADS

Title: Die Feinstruktur von photosphärischen Fackeln
Authors: Mehltretter, J. P.
Bibcode: 1975MitAG..36..138M
Altcode:
  No abstract at ADS

Title: Observations of Photospheric Faculae at the Center of the
    Solar Disk
Authors: Mehltretter, J. P.
Bibcode: 1974SoPh...38...43M
Altcode:
  Observations, in the near UV with very high spatial resolution,
  obtained with the Sacramento Peak Vacuum Tower Telescope, show that
  photospheric faculae are visible near the center of the disk. Faculae
  consist of bright point-like structures with typical dimensions
  of 100-200 km, and appear to be concentrated in the intergranular
  space. Preliminary results on measurements of size, brightness, life
  time, and on interaction of facular structures with granulation are
  presented, which support the view that faculae are identical with the
  recently discovered `solar filigree.' Phenomenological arguments are
  discussed concerning the suggestion that facular points may represent
  magnetic flux concentrations in the photosphere.

Title: Fluctuations of Brightness and Vertical Velocity at Various
    Heights in the Photosphere
Authors: Canfield, Richard C.; Mehltretter, J. P.
Bibcode: 1973SoPh...33...33C
Altcode:
  In a spectrogram of exceptionally high spatial resolution, brightness
  and velocity fluctuations in seven weak to medium-strong Fe I lines
  have been measured and analyzed. Heights of formation of these lines
  have been computed using the Harvard-Smithsonian Reference Atmosphere
  (Gingerich et al., 1972), taking into account departures from LTE.

Title: Studies of Granular Velocities. III: The Influence of Finite
    Spectral and Spatial Resolution upon the Measurement of Granular
    Doppler Shifts
Authors: Mehltretter, J. P.
Bibcode: 1973SoPh...30...19M
Altcode:
  The process of measuring granular velocity fields with an instrument
  having finite spectral and spatial resolution is investigated for
  the case that (1) a weak Fraunhofer line is used, (2) the velocity is
  constant with height in the solar atmosphere, (3) the original Doppler
  shifts are of the same order of magnitude as the `intrinsic" width
  of the line (width observed with infinitely high spectral and spatial
  resolution), (4) continuum brightness and line strength fluctuations
  are superimposed onto the velocity field.

Title: On the rms Intensity Fluctuation of Solar Granulation
Authors: Mehltretter, J. P.
Bibcode: 1971SoPh...19...32M
Altcode:
  Using a selected high definition granulation photograph obtained with
  a 40 cm aperture telescope from the ground, a new determination of
  the rms intensity fluctuation is attempted. We find, at λ5500 Å,
  a value of 0.058 without, of 0.067 with correction for theoretical
  diffraction only, and 0.095 ± 0.015 as the most probable value,
  if the differences between our power spectrum and those given in the
  literature is interpreted as due to a residual seeing of σ = 0.″3
  in our photograph.

Title: Erratum: "Studies of granular velocities. II. Statistical
    analysis of two high-resolution spectrograms" [Sol. Phys., Vol. 16,
    p. 253 - 271 (1971)].
Authors: Mehltretter, J. P.
Bibcode: 1971SoPh...18..510M
Altcode:
  No abstract at ADS

Title: Studies of Granular Velocities. II: Statistical Analysis of
    Two High-Resolution Spectrograms
Authors: Mehltretter, J. P.
Bibcode: 1971SoPh...16..253M
Altcode:
  Continuum brightness and Doppler velocity fluctuations in the lines λ
  6301.5 and λ 6302.5 Å of FeI, measured in two selected spectrograms,
  are analysed by standard statistical (power- and coherence spectrum)
  methods. It is shown qualitatively that the oscillatory component of
  the velocity fluctuations (at spatial wavelengths &gt; 4″) decreases,
  while the supposedly `granular' component (at spatial wavelengths
  &lt; 4″) as well as the coherence between brightness and velocity
  fluctuations increases with optical depth.

Title: Über den Intensitäts-Kontrast der Granulation
Authors: Mehltretter, J. P.
Bibcode: 1971MitAG..30..142M
Altcode:
  No abstract at ADS

Title: Studies of Granular Velocities. I: Granular Doppler Shifts
    and Convective Motion
Authors: Mattig, W.; Mehltretter, J. P.; Nesis, A.
Bibcode: 1969SoPh...10..254M
Altcode:
  The two available methods for determining the rms amplitude of the
  granular convective velocity field, namely the interpretation of line
  profiles, and direct measurements of velocity fluctuations in highly
  resolved spectra, give values (∼ 2 km/sec, and ∼ 0.4 km/sec,
  resp.) which are apparently inconsistent both in magnitude and
  in their dependence upon optical depth. We give both theoretical
  and observational evidence for the working hypothesis, that the
  best resolved spectra mainly show velocity fluctuations due to the
  oscillation of the solar atmosphere, whereas the contribution of the
  granular velocity field is greatly reduced because of atmospheric seeing
  and can be found only as a weak superposition to the oscillatory
  velocity field. Realistic assumptions for the typical size of
  the granulation (2″.5) and for the `seeing parameter' (1″),
  together with a simplified model of the granular velocity field,
  lead to correction factors of 30 to 40 between the true and observed
  amplitudes of the granular velocities.

Title: On π-Components in Zeeman-Split Lines of the Umbra Spectrum
Authors: Mehltretter, J. P.
Bibcode: 1969SoPh....9..387M
Altcode:
  No abstract at ADS

Title: Inhomogene Sonnenmodelle und Geschwindigkeitsfluktuationen
    der Granulation
Authors: Mattig, W.; Mehltretter, J. P.
Bibcode: 1969MitAG..27..204M
Altcode:
  No abstract at ADS

Title: Fine Structure of Brightness, Velocity and Magnetic Field in
    the Penumbra
Authors: Mattig, W.; Mehltretter, J. P.
Bibcode: 1968IAUS...35..187M
Altcode:
  No abstract at ADS

Title: Étalonnage de la source luminescente de l'Institut
    d'Astrophysique de Paris
Authors: Mehltretter, J. P.
Bibcode: 1961AnAp...24...40M
Altcode:
  No abstract at ADS

Title: Ein primärer spektralphotometrischer Standard hoher
    Genauigkeit. Mit 7 Textabbildungen
Authors: Mehltretter, J. P.
Bibcode: 1960ZA.....51...32M
Altcode:
  No abstract at ADS

