Engineering topics

Ake, Thomas B.

Publications and source records attributed to Ake, Thomas B..

8 records

NASA NTRS1996

The Unusual S Star Binary HD 191589

Recently, we discovered with International Ultraviolet Explorer (IUE) an F0-F2 IV-V companion to the T(sub c)-deficient S star HD 191589. If the magnitude difference is (delta)V=3.7, as indicated by several arguments, and E(B-V) = 0.0, we obtain a value of M(sub v)= - 1.5 +/- 0.4 for the Peculiar Red Giant (PRG), too faint for it to be a thermally-pulsing asymptotic giant branch star. According to the binary mass-transfer hypothesis for T(sub c)-deficient PRG's, a white dwarf must be the source of the s-process enhancement of the current primary star, but it cannot be seen because of the presence of the secondary. If such is the case, the F-star companion may also have been contaminated by s-process material. High-dispersion IUE observations indicate an enhancement of Zr II in the photosphere of the F-star as well. Thus, HD 191589 is likely a triple system, where what was once the most massive component of the system has polluted both of its companions with s-process material. One of these is the current S star, while the other is the companion still near the main sequence.

Ake, Thomas B.↗

NASA NTRS1993

Ultraviolet and optical studies of binaries with luminous cool primaries and hot companions. IV - Further IUE detections

We have obtained IUE spectra for 31 middle and late-type giant and supergiant stars whose TD-1 fluxes or ground-based spectra indicate the presence of a hot component, or whose radial velocities indicate an unseen component. Stellar components earlier than type F1 were detected in 22 cases. While 20 of the hot secondaries are seen weakly in optical spectra, two are UV discoveries: HD 58134 and HD 183864. The hot companions are classified accurately by temperature class from their far-UV spectra. The interstellar extinction of each system and the relative luminosities of the components are derived from the UV and optical fluxes, using a new grid of UV intrinsic colors for hot dwarfs. We find that many giant stars apparently have companions which are too hot and hence too luminous for consistency with the primary's spectral classification.

Parsons, Sidney B.↗

NASA NTRS1993

Companions to bright S and MS stars - Technetium deficiency and binarity

To test the popular hypothesis that technetium-deficient stars of spectral types S and MS are mass-transfer binaries, we have searched for ultraviolet light from the putative hot secondaries in spectra taken with the SWP spectrograph of IUE. Although most S and MS stars are apparently thermally pulsing AGB (asymptotic giant branch) stars whose surfaces have been enriched with s-process elements and carbon dredged up from the interior, those stars whose spectra show enhanced s-process elements but no Tc are widely believed to be cooler analogs of the Ba II stars, which apparently owe their unusual abundances to prior mass transfer, the Tc from which has decayed away. We report IUE observations of 15 S and MS stars with the SWP, including the identification of six hot companions. Assembling all the IUE observations made to date, we find clear support for the mass-transfer hypothesis, confirming evidence from other lines of research. We further discuss the ages of the companions and the implications of these discoveries for stellar evolution.

Johnson, Hollis R.↗

NASA NTRS1992

International Ultraviolet Explorer (IUE) ultraviolet spectral atlas of selected astronomical objects

The IUE Ultraviolet Spectral Atlas of Selected Astronomical Objects (or 'the Atlas'), is based on the data that were available in the IUE archive in 1986, and is intended to be a quick reference for the ultraviolet spectra of many categories of astronomical objects. It shows reflected sunlight from the Moon, planets, and asteroids, and also shows emission from comets. Comprehensive compilations of UV spectra for main sequence, subgiant, giant, bright giant, and supergiant stars are published elsewhere. This Atlas contains the spectra for objects occupying other areas of the Hertzsprung-Russell diagram: pre-main sequence stars, chemically peculiar stars, pulsating variables, subluminous stars, and Wolf-Rayet stars. This Atlas also presents phenomena such as the chromospheric and transition region emissions from late-type stars; composite spectra of stars, gas streams, accretion disks and gas envelopes of binary systems; the behavior of gas ejecta shortly after the outburst of novac and supernovac; and the H II regions, planetary nebulae, and supernova remnants. Population 2 stars, globular clusters, and luminous stars in the Magellanic Clouds, M31, and M33, are also included in this publication. Finally, the Atlas gives the ultraviolet spectra of galaxies of different Hubble types and of active galaxies.

Wu, Chi-Chao↗

NASA NTRS1991

First results from the Goddard High-Resolution Spectrograph - The chromosphere of Alpha Tauri

The K5 III star Alpha Tau was observed with the Goddard High Resolution Spectrograph on November 27, 1990 as part of the Science Assessment Program for the HST. The spectra show intersystem and permitted chromospheric emission lines of semiforbidden C II and Si II, Fe II, Fe I, Ni II, and Co II. Resolved profiles of the semiforbidden C II lines indicate a complex chromospheric turbulent velocity distribution with mean value of roughly 24 km/s, while their observed wavelengths indicate a 4 km/s downflow of the semiforbidden C II plasma. Twenty-five new emission lines have been found in the 2320-2370 A region, 17 of which have been identified with the aid of Skylab data obtained above the solar limb, including four lines from Co II (UV 8) and an Fe I (UV 12) line.

Carpenter, Kenneth G.↗

NASA NTRS1990

HD 51956 - A supergiant in an interacting binary

IUE ultraviolet spectral observations reveal that the F supergiant HD 51956 contains a hot companion star partially obscured by warm plasma. Variable absorption features are analogous to those in the strongly interacting system HD 207739. The F type component is apparently transferring matter to a subluminous B type star which originally was the primary component.

Parsons, Sidney B.↗

NASA NTRS1990

A continuing search for companions to PRG stars

Results are presented from observations, made with the SWP spectrograph at low resolution, of Tc-deficient S and C members of the group of chemically peculiar red giant (PRG) stars, which were carried out to search for possible companions to these stars. The results support the hypothesis of Little et al. (1987) and Smith and Lambert (1987, 1988) that the chemical peculiarities of T-deficient S and MS PRG stars have arisen due to mass transfer from white dwarf companions.

Johnson, Hollis R.↗

NASA NTRS1988

A white dwarf companion to the main-sequence star 4 Omicron(1) Orionis and the binary hypothesis for the origin of peculiar red giants

Ultraviolet spectra of the peculiar red giants (PRGs) called MS stars are investigated, and the discovery of a white dwarf (WD) companion to the MS star 4 Omicron(1) Orionis is reported. The observations and data analysis are discussed and compared with those for field WDs in order to derive parameters for the WD and the luminosity of the primary. Detection limits for the other MS stars investigated are derived, and the binary hypothesis for PRGs is reviewed.

Ake, Thomas B.↗