James David Wray

Skylab ultraviolet stellar astronomy experiment S019.

An objective-prism stellar spectrograph of 15-cm aperture was flown on all three Skylab missions. The wavelength region from 1300 A to 5000 A was covered by a special optical system containing a combination of reflecting telescope optics, a CaF(2) objective prism, and an achromatized field corrector lens system of CaF(2) and LiF. Observations of 188 star fields, each covering 4.0 degrees 5.0 degrees , were conducted at the Skylab antisolar airlock with the aid of an articulated mirror system (AMS) which allowed acquisition within 30 degrees degrees 360 degrees band of the sky.

Space Schmidt Telescope

An important part of a balanced future program in space astronomy is a fast, wide-angle telescope (a Space Schmidt) capable of imaging in the ground-inaccessible ultraviolet wave-length range (1100-3000 Å) and capable of reaching substantially fainter background light levels in the visible and near-infrared than are groundbased telescopes (limited by airglow sky background). In 1978, NASA appointed a working group to assess the scientific need and objectives for such a telescope, and to study its feasibility of implementation. In the latter task, the working group was assisted by the Goddard Space Flight Center and by the Perkin Elmer Optical Technology Division (under contract to GSFC). Among the principal observational objectives which were outlined are: Detection of hidden hot objects UV morphology of galaxies Determine presence of dust in galactic fields and extragalactic objects Detection and study of faint extended objects Detection and study of emission line objects Observation of solar system objects (particularly diffuse ones). In addition to the scientific objectives, other concerns such as technical feasibility, complexity, and cost resulted in the following guidelines for the engineering aspects of the feasibility study: Confine space to one orbiter pallet. Use one of the standard pointing systems. Minimize cost. 5 degree field of view 0.75 m diameter aperture, minimum 1.0 arc sec image resolution Fast focal ratio (~ f/3.0) 170 mm diameter detector format (~ 10 μm pixels). The feasibility study determined that all of these specifications could be met with reason-able assurance, and baseline configurations were derived for the telescope optics, structure, and electrographic detector. Supporting studies of these and various other aspects of the telescope system are continuing. Since completion of the study, prospects for a long-duration space platform (as an alternative to extended-duration Spacelab missions) have come to the forefront, resulting in significant changes in the program plan. By far the most important of these is that the baseline scientific objective can now be upgraded (from the observation of a few dozen selected fields of special interest) to a complete full-sky survey in the far-ultraviolet to a limiting V magnitude (for an unreddened BO star) of mv = +27.0. An international consortium of astronomical institutions has now joined together in proposing to carry out this program from instrument development to the production and distribution of the final far-ultraviolet all-sky survey atlas.

Spectral Classification with Objective-Prism Spectra from Skylab

During the Skylab I, II and III missions, ultraviolet spectra were obtained in 188 fields with a 15 cm aperture objective-prism spectrograph. The instrument has been described by Henize, Wray, Parsons, Benedict, Bruhweiler, Rybski and O’Callaghan (1975; hereafter referred to as Paper I).

Large-format electrographic and array detectors for a space Schmidt imaging telescope

Possible optical designs of imaging detectors for the spaceborne Schmidt telescope proposed by Carruthers et al. (1990) are discussed, surveying the currently or potentially available technology. Consideration is given to FUV electrographic detectors of large format (e.g., 120 mm with 10-micron resolution) using CsI photocathodes, the possible extension of the same technology to the mid-UV using Cs2Te instead of CsI, large CCD arrays for the visible and NIR, electron-bombarded CCDs for the FUV and mid-UV, and the data handling and processing requirements of these detectors.

Space Schmidt imaging telescope: optical concept and astrophysical objectives

The design concept of a wide-field astronomical imaging telescope for use as a payload on an unmanned space platform, a Space Station attached payload, or a Delta-class Explorer is described. The instrument is based on a space Schmidt telescope concept studied by NASA and ESA (1979) for Spacelab missions. The astrophysical objectives include all-sky surveys in the UV and NIR ranges. Objects of interest include very hot and very cool stars and the interstellar medium. The UV range is inaccessible from the ground, and large-area surveys and sensitive imagery of diffuse sources are impractical with current or planned UV space telescopes. The NIR range is severely compromised in ground-based observations, particularly of diffuse sources, by airglow emissions, and no wide-field NIR space telescopes are currently approved for flight.

Middle- and far-ultraviolet observations of hot white dwarfs

Observations of HD 149499 B, the previously unrecognized white dwarf star found by the Skylab ultraviolet objective-prism survey, are discussed. Spectra of the binary HD 149499 AB were obtained by the short wavelength and long wavelength cameras of the IUE, and converted into fluxes. The absorption line strengths of the white dwarf secondary indicate a He/H composition ratio greater than or equal to 1. Comparison with model atmospheres of the IUE data suggests a temperature of around 93,000 K for HD 149499 B, while comparison with visual magnitude data indicates a temperature of 82,000 K. Either temperature value would make the star the hottest white dwarf for which reasonably reliable temperature estimates are available. Future work intended includes the repetition of the Skylab ultraviolet experiment on Spacelab for the detection of a complete sample of hot white dwarfs and subdwarfs.

The University of Texas Catalog of Ultraviolet and Optical Stellar Data

At the University of Texas we are working on the reduction and analysis of ultraviolet stellar spectra obtained with the S–019 experiment on Skylab (Karl Henize, principal investigator). Our objective prism photographs recorded nearly 10, 000 stars at wavelengths shortward of 3000A, many of them of 9th or 10th visual mag., and for proper analysis we need to assemble ground-based data into a workable master catalog. The most immediate application of this catalog will be computer simulation of the ultraviolet photographs in order to point out significant anomalies with respect to previous knowledge. We need to have a catalog, then, which is as complete as possible in terms of the existence of early-type stars to at least 10th mag., their spectral types, photometry, known peculiarities, duplicity, and so forth. Also the master catalog must contain only a single value for each magnitude and for the spectral type, rather than a listing of various determinations, in order to be useful for the simulation. This means that auxiliary data files are needed for recording data in more detail so that the master catalog may be kept at a workable size, while at the same time the basic data are readily available.

Some Astronomical Applications For Precision High-Speed Computer Interfaced Microdensitometry

With the advent of modern precision high speed microdensitometers operating under control of general purpose ii-computers, vast areas of research have suddenly beco e available which, until only recently, were largely inaccessible due simply to the constraint of limited available time. The intent of this paper is to present a general discussion of a number of applications for which such a system (one which we are currently using) is suited. Neither is the list of applications exhaustive, nor is our system the last word in this rapidly developing technology. Even so, with consideration of these finite limitations the research capabilities of such a system seem all the more impressive.