Engineering topics

Drilling, J. S.

Publications and source records attributed to Drilling, J. S..

At least 19 records

NASA NTRS1989

Non-LTE analysis of extremely helium-rich stars. The hot sdO stars LSE 153, 259 and 263

Results of a non-LTE fine analysis based mainly on high-resolution CASPEC spectra for three extremely helium-rich sdO stars are discussed in order to explain hydrogen deficiency in single stars. High temperature (Teff = 70,000 to 75,000 K) and a position in the log Teff - log g diagram were found close to the Eddington limit. Various abundance estimates are derived for hydrogen (upper limits only), carbon, nitrogen, and magnesium. Hydrogen is reduced to less than 10 percent by number in LSE 153 and LSE 263, and to less than 5 percent in LSE 259. The hydrogen deficiency is accompanied by nitrogen- and carbon-enrichment in LSE 153 and LSE 259 only. In LSE 263, carbon is depleted by about 1 dex. Stellar masses obtained by assuming that a core mass-luminosity relation holds for these stars, were found to be in the range 0.6-0.9 solar mass, yielding luminosities log L/L:solar = 3.7-4.5. Two of the program stars (LSE 153 and 259) appear to be possible successors of the R CrB and helium B stars, whereas the third star (LSE 263) displays a much lower carbon content in its photosphere making it an exceptional case among the known hydrogen deficient stars.

Husfeld, D.↗

NASA NTRS1989

On the nature of newly formed dust around the hydrogen-deficient star V348 Sagittarii

IUE spectra of V348 Sgr have been used to determine the extinction law from 1250 to 3080 A for circumstellar material recently ejected from it. This law differs from the standard extinction law in showing a bump at 2500 A rather than 2200 A, and in showing much lower extinction values for lambda less than 2000 A. These differences are attributed to the dust grains being formed in a hydrogen-poor environment in the case of V348 Sgr, and thus lend support to those theories of the standard extinction law which attribute its properties to the dust grains being formed in a hydrogen-rich environment.

Drilling, J. S.↗

NASA NTRS1988

High-resolution spectroscopy of central stars of planetary nebulae - LSS 1362

High resolution spectra of the hot sdO star LSS 1362, a central star of a planetary nebula, are analyzed by means of model atmosphere techniques. Improved NLTE model atmospheres based on the newly developed 'accelerated lambda iteration' method are used. The very high effective temperature (100000 K) derived previously from the UV energy distribution is confirmed. The surface gravity (log g = 5.3) and a normal helium abundance are derived. A mass of 0.65 solar mass and a luminosity of 10 exp 3.9 solar luminosities result from a comparison with evolutionary tracks. The distance is 1.1 kpc and the nebula has a diameter of about 0.25 pc to 0.5 pc. Weak photospheric emission lines of He II, CIV, Nv, and O v are detected. These lines are slightly blue-shifted with respect to the absorption line spectrum which is regarded as evidence for an atmospheric velocity field. It is conjectured that the observed broadening of the metal lines (25 km/s) may be caused by the velocity field rather than by rotation.

Heber, U.↗

NASA NTRS1987

A spectroscopic and photometric survey of OB+ stars

Image-tube spectra (with dispersions of 40-90 A/mm) and UBV photometry of OB+ stars have been obtained at Cerro Tololo and Kitt Peak. The survey is complete to galactic latitudes of + or - 30 deg for galactic longitudes of between 300 and 60 deg. Most of the stars are found to be O-type and B-type supergiants, and 378 new O-type and B-type detections have been identified.

Drilling, J. S.↗

NASA NTRS1986

Basic data on hydrogen-deficient stars

The current state of knowledge on the diistribution and motions of various types of hydrogen-deficient stars, and of their positions in the H-R diagram, is reviewed. It is concluded that the extreme helium stars (with the exception of the H-deficient binaries) and cool hydrogen-deficient stars belong to the population of the Galactic nuclear bulge, whereas the intermediate helium stars are young stars of Population I. The helium-rich sdO stars appear to be a local sample which is predominantly Population I.

Drilling, J. S.↗

NASA NTRS1986

High resolution spectroscopy of six new extreme helium stars

High resolution spectra of six newly discovered extreme helium stars are presented. LSS 5121 is shown to be a spectroscopical twin of the hot extreme helium star HD 160641. A preliminary LTE analysis of LSS 3184 yielded an effective temperature of 22,000 K and a surface gravity of log g = 3.2. Four stars form a new subgroup, classified by sharp-lined He I spectra and pronounced O II spectra, and it is conjectured that these lie close to the Eddington limit. The whole group of extreme helium stars apparently is inhomogeneous with respect to luminosity to mass ratio and chemical composition.

Heber, U.↗

NASA NTRS1986

NLTE-analysis of three extremely helium-rich O-type subdwarfs

Three extremely helium-rich sdO stars (LSE 153, LSE 259 and LSE 263) were analyzed spectroscopically by means of detailed NLTE model atmospheres. These stars are very hot, with effective temperatures ranging from 70,000 to 75,000 K and gravities between log g = 4.4 and 4.9. Upper limits for the hydrogen abundance were also derived. The evolutionary status of the sdO stars is discussed and it is concluded that they evolve from the asymptotic giant branch towards the white dwarf stage. A possible evolutionary link between these hot stars and the extreme helium stars of spectral type B is discussed.

Husfeld, D.↗

NASA NTRS1985

LSS 2018 - A double-lined spectroscopic binary central star with an extremely large reflection effect

LSS 2018, the central star of the planetary nebulae DS1, was found to be a double-lined spectroscopic binary with a period of 8.571 hours. Light variations with the same period were observed in U, B, and V; in the wavelength regions defined by the two IUE cameras; and in the strength of the CIII 4647 emission line. The light variations can be accurately predicted by a simple reflection effect, and an analysis of the light curves yields the angular diameter and effective temperature of the primary, the radii of the two stars in terms of their separation, and the inclination of the system. Analysis of the radial velocities then yields the masses of the two stars, their separation, the distance of the system, the absolute magnitude of the primary, and the size of the nebula.

Drilling, J. S.↗

NASA NTRS1985

On the progenitors of white dwarfs

In view of the direct observational evidence presented here, the immediate progenitors of white dwarfs are the central stars of planetary nebulae in as many as 80 percent of all cases; secondary progenitors being other postasymptotic giant branch objects, to the extent of nearly 20 percent, and posthorizontal branch objects insufficiently massive to climb the asymptotic giant branch, with about 0.7 percent. The combined birth rate of these objects, at 2-3 x 10 to the -12th/cu pc per year, is in satisfactory agreement with the death rate of main sequence stars and the birth rate of white dwarfs.

Drilling, J. S.↗

NASA NTRS1985

On the ultraviolet iron spectrum of pre-white dwarfs

Numerous lines of Fe V, Fe VI, and Fe VII have been detected in high-resolution IUE spectra of two central stars and a number of very hot subdwarfs. The strengths of these lines vary widely from star to star, suggesting that the abundance of iron in the atmospheres of the immediate progenitors of white dwarfs is strongly variable. A possible explanation is elemental separation by gravity and radiation pressure.

Schoenberner, D.↗

NASA NTRS1985

On the progenitors of white dwarfs

Direct observational evidence is presented which indicates that the immediate progenitors of white dwarfs are the central stars of planetary nebulae (approximately 70%), other post-AGB objects (approximately 30%), and post-HB objects not massive enough to climb the AGB (approximately 0.3%). The combined birth rate for these objects is in satisfactory agreement with the death rate of main-sequence stars and the birth rate of white dwarfs.

Drilling, J. S.↗

NASA NTRS1985

LSS 2018: A double-lined spectroscopic binary central star with an extremely large reflection effect

LSS 2018, the central star of the planetry nebulae DS1, was found to be a double-lined spectroscopic binary with a period of 8.571 hours. Light variations with the same period were observed in U, B, and V; in the wavelength regions defined by the two IUE cameras; and in the strength of the CIII 4647 emission line. The light variations can be accurately predicted by a simple reflection effect, and an analysis of the light curves yields the angular diameter and effective temperature of the primary, the radii of the two stars in terms of their separation, and the inclination of the system. Analysis of the radial velocities then yields the masses of the two stars, their separation, the distance of the system, the absolute magnitude of the primary, and the size of the nebula.

Drilling, J. S.↗

NASA NTRS1984

Far-ultraviolet spectrophotometry of two very hot O type subdwarfs

As a result of a spectroscopic survey of stars classified as nonemission OB+, Drilling (1983) has detected 12 new subluminous O stars. It was found that these stars are the hottest known O type subdwarfs. The effective temperatures of the stars are 60,000 K or higher. It has been possible to observe two of these stars with Voyager 1, taking into account LSE 21 and LS IV +10.9 deg. LSE 21 is one of the hottest of the new subdwarfs, with an effective temperature of at least 100,000 K. The optical spectrum indicates a hydrogen-rich atmosphere of high surface gravity. LX IV +10.9 deg is one of the cooler objects with an effective temperature of 65,000 K. The optical spectrum indicates an extremely helium-rich atmosphere and a somewhat lower surface gravity than LSE 21. The Voyager 1 observations confirm the temperature scale set up by Schoenberger and Drilling (1984) for the hottest O type subdwarfs.

Drilling, J. S.↗

NASA NTRS1984

The elusive variability of BD + 10.2179 deg

High-speed photometry of the hydrogen-deficient star BD + 10.2179 deg has been obtained in order to ascertain if it is presently pulsationally unstable with the previously published period of 0.162 to 0.164 d. During an observing run of 0.21 d no pulsations were observed above the noise limit of 0.002 mag. Either the previously published period is not real or the star is no longer pulsating.

Drilling, J. S.↗

NASA NTRS1984

Effective temperatures and luminosities of very hot O type subdwarfs

Twelve very hot O-type subdwarfs were observed with the IUE-satellite in the low dispersion mode. Temperatures were derived from the slopes of the UV continua and distances were estimated from the color excesses. Most of them are hotter than 60,000 K, i.e., they are the hottest known subdwarfs. From their spectral appearance and location in a H.R.-diagram, they form a rather inhomogeneous group. Three of them turned out to be central stars or nearly central stars, and four are definitely near the white dwarf stage. The surface helium to hydrogen ratio varies from about normal to the extreme case. Most of them appear to be post EHB objectives of 0.5 solar mass with a helium burning shell as their energy source, and their peculiar helium-to-hydrogen ratios are most likely the result of diffusion and convective mixing in surface layers. Previously announced in STAR as N83-23254

Schonberner, D.↗

NASA NTRS1984

Spectrophotometry of extreme helium stars - Ultraviolet fluxes and effective temperatures

Ultraviolet flux distributions are presented for the extremely helium rich stars BD +10 deg 2179, HD 124448, LSS 3378, BD -9 deg 4395, LSE 78, HD 160641, LSIV -1 deg 2, BD 1 deg 3438, HD 168476, MV Sgr, LS IV-14 deg 109 (CD -35 deg 11760), LSII +33 deg 5 and BD +1 deg 4381 (LSIV +2 deg 13) obtained with the International Ultraviolet Explorer (IUE). Broadband photometry and a newly computed grid of line blanketed model atmospheres were used to determine accurate angular diameters and total stellar fluxes. The resultant effective temperatures are in most cases in satisfactory agreement with those based on broadband photometry and/or high resolution spectroscopy in the visible. For two objects, LSII +33 deg 5 and LSE 78, disagreement was found between the IUE observations and broadband photometry: the colors predict temperatures around 20,000 K, whereas the UV spectra indicate much lower photospheric temperatures of 14,000 to 15,000 K. The new temperature scale for extreme helium stars extends to lower effective temperatures than that of Heber and Schoenberner (1981) and covers the range from 8,500 K to 32,000 K. Previously announced in STAR as N83-24433

Heber, U.↗

NASA NTRS1984

LSS 4300 - A hot counterpart of Upsilon Sagittarii and KS Persei?

A number of recent observations indicate that the star LSS 4300 (HDE 320156) is a high-temperature analog of the hydrogen-deficient binaries Upsilon Sgr and KS Per. A preliminary model-atmosphere analysis based on high dispersion spectra obtained at Kitt Peak and Cerro Tololo yields Teff = 14,400 K, log (g) = 1.4, n(H)/n(He) = 0.003, and n(N)/n(C) = 20 for the visible component. The optical emission-line spectrum of LSS 4300 is nearly identical to that of Upsilon Sgr, including strong, broad H-alpha, Fe II, and forbidden Ca II emission; and JHKL photometry obtained at Cerr Tololo reveals an infrared excess nearly identical to that of Upsilon Sgr. It is suggested that LSS 4300, like Upsilon Sgr and KS Per, is a close binary system consisting of a helium supergiant of about 1 solar mass, which is undergoing its second mass loss, and a less luminous secondary, which is accreting matter from the primary.

Schoenberner, D.↗

NASA NTRS1984

Ultraviolet spectroscopy of selected astronomical sources

The birth rates of various kinds of white dwarf progenitors are estimated and the spectra of two very hot O-type white dwarfs are analyzed. The effective temperature of LSE 21 was found to be in excess of 100,000 K. The abundance of iron in the atmospheres of two central stars and numerous very hot O-type subdwarfs was found to be strongly variable. Results obtained by high resolution optical spectroscopy, UBV photometry, and low resolution IUE spectrophotometry for LSS 2018, the central star of the planetary nebulae DS1, are summarized. A planetary nebula surrounding the very hot subdwarf LSS 1362 was discovered. Analysis of results obtained by high resolution optical spectra shows agreement with an effective temperature of 110,000 K derived using low resolution IUE observations.

Drilling, J. S.↗