Search Publications
The EUVE and IUE Spectra of the Hot DA White Dwarf GD 659
Barstow, M. A.; Bruhweiler, F. C.; Sion, E. M. +1 more
We present recent EUVE spectra and new co-added lUE echelle spectra of the hot DA white dwarf GD 659. Our EUVE spectra show the expected continuum of a pure H DA white dwarf, from which we derive upper limits on the photospheric abundances for He, C, N, O, and Si. Our co-added lUE echelle spectrum shows, in addition to the common interstellar line…
The Circumstellar Nature of the Metallic Features in a Hot DA White Dwarf
Andersen, J.; Bruhweiler, F. C.; Holberg, J. B.
A new co-added IUE echelle spectrum of the bright DA white dwarf CD -38 deg 10980, together with a newly determined radial velocity for this star, indicate that the sharp lined Si and C absorption features seen in the UV are clearly circumstellar in origin. Absorption in both excited and ground state transitions occurs at a velocity displaced by -…
New Insights into Nonradiative Heating in Late A Star Chromospheres
Walter, Frederick M.; Linsky, Jeffrey L.; Matthews, Lynn D.
Using new and archival spectra from the Goddard High Resolution Spectrograph, we have searched for evidence of chromospheric and transition region emission in six stars of mid to late A spectral type. Two of the stars, α Aql (A7 IV-V) and alpha Cep (A7 IV-V), show emission in the C II 1335 Å doublet, confirming the presence of hot plasma with temp…
The Structure of Wolf-Rayet Winds. I. Observation of Ionization Stratification in WR 6 and WR 111
Schulte-Ladbeck, Regina E.; Eenens, Philippe R. J.; Davis, Kevin
Although it is widely believed that the winds of Wolf-Rayet stars are driven by radiation pressure, a major problem has been to explain theoretically the observation of very efficient conversion of radiative momentum to the gas. Known as the "momentum problem," this has led to alternative models in which the radiation force is only one of the forc…
The Axis Ratio Distribution of Faint Galaxies: Evidence for a Population of Dwarf Galaxies at I approximately 20.5
Casertano, Stefano; Im, Myungshin; Griffiths, Richard E. +1 more
The axis ratio distribution of faint galaxies observed by the Hubble Space Telescope (HST) as part of the Medium Deep Survey key project suggests that a very large fraction of the total population at magnitudes I >= 20 mag consists of a class of galaxies with luminosity profile, axis ratio distribution, angular size, and color that resemble loc…
MG II H and K Profiles in High-Luminosity, Late-Type Stars
Carpenter, K. G.; Robinson, R. D.
Using high-resolution spectroscopic data taken with the Goddard High Resolution Spectrographic (GHRS) aboard the Hubble Space Telescope (HST) and with the International Ultraviolet Explorer (IUE) satellite, we compare the profiles of the Mg II h and k lines seen in stars with spectral types ranging from early K through mid-M and luminosities from …
Galaxy Clustering Statistics of Hubble Space Telescope Medium Deep Survey WF/PC Images
Im, M.; Griffiths, R. E.; Casertano, S. +2 more
We investigate the clustering properties of galaxies observed to I ≲ 23 mag in prerefurbishment WF/PC images obtained for the Medium Deep Survey HST Key project. The present study is superior to earlier ground-based galaxy clustering studies in its subarcsecond resolution of close pairs of objects and the depths to which systematic galaxy classifi…
Probing the Galactic Disk and Halo. II. Hot Interstellar Gas toward the Inner Galaxy Star HD 156359
Sembach, Kenneth R.; Savage, Blair D.; Lu, Limin
We present Goddard High Resolution Spectrograph intermediate-resolution measurements of the 1233-1256 A spectral region of HD 156396, a halo star at l = 328.7 deg, b = -14.5 deg in the inner Galaxy with a line-of sight distance of 11.1 kpc and a z-distance of -2.8 kpc. The data have a resolution of 18 km/s Full Width at Half Maximum (FWHM) and a s…
RE 0044+09: A New K Dwarf Rapid Rotator with a White Dwarf Companion?
Brown, Alexander; Jeffries, Robin D.; James, David J. +7 more
We report the discovery of a new K dwarf rapid rotator with a potential white dwarf companion. The white dwarf accounts for over 90% of the observed extreme ultraviolet flux detected from this system. Analysis of ROSAT Wide Field Camera (WFC) and IUE data both suggest a white dwarf temperature of approximately 28,700 K. Optical photometry and the …
Chromospheric Models for ALTAIR (A7 IV--V)
Talavera, A.; Kondo, Y.; Bruhweiler, F. +5 more
The star, Altair (A7 IV-V), is clearly shown to have Lyman-alpha emission of chromospheric origin, while no evidence is found for the Mg II emission reported in previous investigations. We present non-Local Thermodymanic Equilibrium (non-LTE) semiempirical models incorporating partial redistribution of the chromosphere of Altair that reproduce the…