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. 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−1, 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 > 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. 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