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Wray, J. D.

Publications and source records attributed to Wray, J. D..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Comparison of winds in the Small Magellanic Cloud and galactic early-type stars

IUE low-resolution spectra of 11 OB stars in the Small Magellanic Cloud reveal considerably lower wind velocities than corresponding galactic stars. The reduced effectiveness of radiative acceleration due to lower abundances of heavy elements in the SMC is believed to be responsible for this effect. The absorption strengths of the SMC P Cygni profiles are somewhat weaker in Si IV and much weaker in C IV. Crude estimates of relative mass-loss rates suggest that the observed differences may be dominated by the differing relative abundances of Si and C, although a lower degree of wind ionization or lower mass-loss rates for the SMC stars cannot be ruled out.

Bruhweiler, F. C.↗
NASA NTRS1982

Space Schmidt telescope

The complete survey takes in 3627 fields, each 4.87 deg in diameter, arranged in a hexagonal pattern superimposed on the celestial equatorial coordinate system. The declination bands are spaced every 3 deg, 20 min. The optical instrument is a folded all-reflecting Schmidt system with an aperture of 0.74 m, a focal length of 2.0 m (f/2.7), a circlar field with a diameter of 4.87 deg, and a limiting image diameter of less than 2 arcsec over the entire field. The detector is an electrographic camera having a photocathode diameter of 170 mm. In discussing the telescope structure, it is pointed out that the optical support system is to be of graphite-epoxy construction. The focal tolerance (the most critical optical tolerance) is to be + or - 12 microns. Regarding contamination control, it is expected that with appropriate design it will be possible to operate in sunlight for observations in a restricted portion of the sky, at least more than 90 deg from the sun, depending on the geometry and reflectivity of the platform or spacecraft configuration.

Wray, J. D.↗
NASA NTRS1981

A classification system for O-B2 stars based on the Si IV and C IV resonance lines

Low-dispersion ultraviolet spectra from Skylab Experiment S-019 are used to explore the variations of Si IV and C IV line strengths with temperature and luminosity. These considerations lead to a classification system in which the Si/C ratio is used to discriminate luminosity among the O stars and temperature among the O9-B2 stars of lower luminosity. Stars falling in these two regimes may be distinguished either by the presence of C IV emission or on the basis of C IV absorption strength. The log(Si IV/C IV) vs C IV diagram is proposed as a primary tool in such a classification system. The rapid variation in the Si IV/C IV ratio from less than 1/10 at O9 to greater than 10 at B1.5 for luminosity class III-V stars appears to be an especially useful criterion for the temperature classification of stars in this spectral range.

Henize, K. G.↗
NASA NTRS1979

HD 149499 B - The hottest white dwarf

IUE spectra of the white dwarf component of HD 149499, discovered from the Skylab experiments S-019 UV survey, show prominent lines of He II. The star appears to be helium-rich with He/H not less than 1. The ultraviolet fluxes show the temperature to be within the range 70,000-100,000 K, with the most probable value near 85,000 K.

Wray, J. D.↗
NASA NTRS1979

Catalog of far-ultraviolet objective-prism spectrophotometry: Skylab experiment S-019, ultraviolet steller astronomy

Ultraviolet stellar spectra in the wavelength region from 1300 to 5000 A (130 to 500) were photographed during the three manned Skylab missions using a 15 cm aperture objective-prism telescope. The prismatic dispersion varied from 58 A mm/1 at 1400 A to 1600 A mm/1 at 3000 A. Approximately 1000 spectra representing 500 stars were measured and reduced to observed fluxes. About 100 stars show absorption lines of Si IV, C IV, or C II. Numerous line features are also recorded in supergiant stars, shell stars, A and F stars, and Wolf-Rayet stars. Most of the stars in the catalog are of spectral class B, with a number of O and A type stars and a sampling of WC, WN, F and C type stars. Spectrophotometric results are tabulated for these 500 stars.

Henize, K. G.↗
NASA NTRS1979

C IV resonance line profiles in O stars

Graphs of normalized fluxes derived from objective-prism spectra (from the S-019 experiment on Skylab), and C IV profiles are presented. The C IV resonance profile, when studied with respect to bolometric magnitude and effective temperature, reveals mass loss conditions without requiring precise mass loss rates. There is a clear trend in the C IV feature toward more fully developed P Cygni profiles at higher luminosities, and a significant velocity shift in the C IV absorption down to bolometric magnitude approximately equal to -7.7.

Parsons, S. B.↗
NASA NTRS1979

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.

Parsons, S. B.↗
NASA NTRS1978

A hot subluminous star - HDE 283048

The star HDE 283048 located at alpha = 3(h)50(m)3, delta = +25 deg 36 min shows a strong ultraviolet continuum. Ground-based observations indicate a hot-dominated composite spectrum. Several lines of evidence suggest that the hot component is a hot subdwarf.

Laget, M.↗
NASA NTRS1977

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 CaF2 objective prism, and an achromatized field-corrector lens system of CaF2 and LiF. Observations of 188 star fields, each covering 4.0 x 5.0 deg of arc, were conducted at the Skylab antisolar airlock with the aid of an articulated mirror system which allowed acquisition within a 30 by 360 deg band of the sky.

Ocallaghan, F. G.↗
NASA NTRS1977

The University of Texas catalog of ultraviolet and optical stellar data

The paper describes a plan to assemble a master catalog of early-type stars to at least 10th magnitude, containing a single value for each magnitude and the spectral type, with information on photometry, known peculiarities, duplicity, etc., which will serve as a collection of ground-based data to aid in the reduction and analysis of ultraviolet spectra obtained with the S-019 experiment on Skylab, in which objective prism photographs recorded nearly 10,000 stars at wavelengths shortward of 3000 A. The starting point is the Celescope Identification Catalog; several other catalogs will be compared and merged with this data base. The format for recording the wanted data on magnetic tape and the procedure for assembling the master file are discussed.

Parsons, S. B.↗
NASA NTRS1976

Skylab ultraviolet stellar spectra - Emission lines from the Beta Lyrae system

Observations of Beta Lyr with the Skylab S-019 ultraviolet objective-prism spectrograph show numerous emission lines in the region from 1400 to 2300 A. Some variations in line strength between phases 0.25 and 0.50 are seen, which probably explain the shallowness of the OAO-2 light curve at 1910 A. Many of the emission lines are probably due to intercombination transitions, thus confirming the concept that the emission is produced by collisional excitation in low-density clouds of hot gas.

Kondo, Y.↗
NASA NTRS1976

Skylab ultraviolet stellar spectra - A new white dwarf, HD 149499 B

The letter reports the discovery of a cool star with excess brightness in the vacuum ultraviolet on an objective-prism photograph obtained during the second Skylab mission. This star, HD 149499, is of type K0 V and has a companion with an apparent magnitude of about 11.8; the relatively flat UV spectrum observed at the position of HD 149499 is characteristic of a 10th or 11th magnitude unreddened O- or early B-type star. It is shown that the excess VUV brightness is due to the companion, HD 149499B, which probably lies in the region of the H-R diagram occupied by the hot white dwarfs. Inspection of white dwarf lists indicates that this star is the sixth or seventh brightest white dwarf known. A maximum orbital motion of 0.025 arcsec/yr is estimated along with a period of just under 500 yr.

Parsons, S. B.↗
NASA NTRS1976

Skylab ultraviolet stellar spectra - Cool stars with hot secondaries

A hot companion to the G5 III star HR 3080, a single-line spectroscopic binary, has been discovered from spectra in the vacuum-ultraviolet. The companion must be a subdwarf or pre-white dwarf. A list of previously known systems of the zeta Aur and VV Cep type observed with the ultraviolet spectrograph on Skylab is also given.

Parsons, S. B.↗
NASA NTRS1976

The Skylab S019 ultraviolet spectra of HD 153919 (=3U 1700-37) and HDE 226868 (=Cyg X-1)

Ultraviolet spectra of HD153919 (=3U1700-37) and HDE226868 (=Cyg X-1) were obtained with the ultraviolet objective-prism spectrograph of Skylab Experiment S019. The data consist of unwidened spectra which extend to 1,600A for HD153919 and to 2,400A for HDE226868. The wavelength resolution is about 2A to 1,400A and 12A at 2,000A. For HD153919, an unwidened spectrum of fair quality and extending to a wavelength of 1,600A was obtained at 22 sup h 08 sup m on 1 September 1973. The energy distribution in this spectrum generally resembles that of other reddened O stars. A break in continuum intensity seems to occur at a wavelength of about 1,720A. There is a suggestion of an emission line on the longward edge of the break but this could be either a chance clumping of grains or else a photographic edge-effect caused by the break.

Kondo, Y.↗
NASA NTRS1976

Ultraviolet stellar spectra obtained on Skylab

A 15-cm aperture f/3 Ritchey-Chretien telescope equipped with a 4 deg calcium fluoride prism was employed in taking objective prism spectra from 1300 to 5000 A in 188 stars, in the three Skylab missions. Spectra of 2 A resolution at 1400 A and 10 A at 2000 A, extending to B0 stars such that V equals 6.5, were taken of 400 stars in the neighborhood of 1500 A. Stellar temperature and luminosity variations are revealed in resonance lines of C IV and Si IV. Profiles of P Cygni type show up in the spectra of all stars with absolute bolometric magnitudes brighter than minus 8.4, implying appreciable outflow of mass. Spectra with emission lines shortward of 2000 A were obtained for 12 WR stars, and spectra of some companion stars dominating the UV spectra are reported.

Henize, K. G.↗
NASA NTRS1975

Ultraviolet stellar astronomy

The author has identified the following significant results. During all three Skylab missions, prism-on observations were obtained in 188 starfields and prism-off observations in 31 starfields. In general, the fields are concentrated in the Milky Way where the frequency of hot stars is highest. These fields cover an area approximately 3660 degrees and include roughly 24 percent of a band 30 deg wide centered on the plane of the Milky Way. A census of stars in the prism-on fields shows that nearly 6,000 stars have measurable flux data at a wavelength of 2600A, that 1,600 have measurable data at 2000A, and that 400 show useful data at 1500A. Obvious absorption or emission features shortward of 2000A are visible in approximately 120 stars. This represents a bonanza of data useful for statistical studies of stellar classification and of interstellar reddening as well as for studies of various types of peculiar stars.

Henize, K. G.↗