explanation blue bibcodes open ADS page with paths to full text
Author name code: mehltretter
ADS astronomy entries on 2022-09-14
author:"Mehltretter, J.P."
---------------------------------------------------------
Title: Alignment tolerances of the proposed Ritchey-Chretien system,
and interferometric control of its alignment
Authors: Mehltretter, J. P.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1979MitAG..45..148S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Project Spectrostratoscope: Balloon-borne solar research
Authors: Mehltretter, J. P.; Mattig, W.; Vonalvensleben, A.
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.
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.
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.
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.
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.
1977MitAG..42..113M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Computer-Processed Granulation Pictures of Project
"Spectro-Stratoscope"
Authors: Wittmann, A.; Mehltretter, J. P.
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.
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.
1976MitAG..40R.162M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Der Flug von Spektro-Stratoskop.
Authors: Mehltretter, J. P.
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.
1976IAUTA..16b..13N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Die Feinstruktur von photosphärischen Fackeln
Authors: Mehltretter, J. P.
1975MitAG..36..138M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Photospheric Faculae at the Center of the
Solar Disk
Authors: Mehltretter, J. P.
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.
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.
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.
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.
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.
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 > 4″) decreases,
while the supposedly `granular' component (at spatial wavelengths
< 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.
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.
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.
1969SoPh....9..387M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Inhomogene Sonnenmodelle und Geschwindigkeitsfluktuationen
der Granulation
Authors: Mattig, W.; Mehltretter, J. P.
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.
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.
1961AnAp...24...40M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ein primärer spektralphotometrischer Standard hoher
Genauigkeit. Mit 7 Textabbildungen
Authors: Mehltretter, J. P.
1960ZA.....51...32M Altcode:
No abstract at ADS