Search Publications
The Galactic Halo and Local Intergalactic Medium toward PKS 2155-304
Boggess, A.; Urry, C. M.; Grady, C. A. +3 more
The first HST GHRS spectra of the bright BL Lacertae object PKS 2155-304, acquired using the G140L configuration show a smooth, featureless continuum with superposed sharp absorption. This absorption is due to both gas in the Galactic halo above the south Galactic pole and what are identified as five to six low redshift Lyα absorption systems aris…
He 3-519: A Peculiar Post-LBV, Pre-WN Star?
Humphreys, Roberta M.; Davidson, Kris; Terzian, Yervant +1 more
We report IUE and ground-based data indicating that the star He 3-519 has a distance of roughly 8 kpc and an absolute bolometric magnitude of about -11, comparable to AG Car. Its luminosity, spectrum, and large, massive circumstellar shell indicate that this may be a post-LBV object which has not yet become a full-fledged WN star. One notable pecu…
Spectroscopic Observations of the Detached Binary PG 1413+015
Bergeron, P.; Green, Richard; Liebert, James +1 more
We present improved estimates of the stellar parameters of the eclipsing, precataclysmic binary system PG 1413 + 015 (GH Vir), which has an orbital period of only 8h16m. Model atmosphere fits a Balmer line profiles yield T(eff) = 48,800 +/- 1200 K and log g = 7.70 +/- 0.11 for the DAO white dwarf primary star, from which a mass of 0.51 +/- 0.04 so…
The Ultraviolet--to--Near-Infrared Spectral Flux Distribution of Four BL Lacertae Objects
Maraschi, L.; Tanzi, E. G.; Chiappetti, L. +3 more
We report on simultaneous UV, optical, and near-IR observations of four BL Lac objects. For three objects (PKS 0118-27, PKS 0301-24, and PKS 1538+14), we find that the spectral flux distribution from 8 x 10^13^ to 2.5 x 10^15^ Hz is well described by a single power law with spectral index α_v_ = 1.2, α_v_ = 1.0, and α_v_ = 1.3, respectively. For H…
The Time Variability of the Ultraviolet Continuum and Lyman-Alpha in 3C 273
Wamsteker, W.; Ulrich, M. -H.; Courvoisier, T. J. -L.
This article presents the light curve of the ultraviolet (UV) continuum flux and of the Lyα emission line of 3C 273 between 1978 and 1992.5. It also presents evidence for a quantitative difference between nearby Seyfert 1 and the quasar 3C 273 regarding the response of the emission lines to UV continuum flux variations. In contrast to what is obse…
On the Chromospheric Structure of zeta Aurigae
Eaton, Joel A.
The chromospheric structure of Zeta Aur is analyzed on the basis of both optical and UV data. Column densities of matter along different lines of sight through the chromosphere are measured by using both Ly-alpha wings and many lines of ionized metals, and they agree to within the errors of measurement. The chromosphere is seen to extend at least …
A New Luminous Blue Variable: R143 in 30 Doradus
Parker, Joel Wm.; Clayton, Geoffrey C.; Conti, Peter S. +1 more
We have discovered that R143 in the Large Magellanic Cloud is a luminous blue variable (LBV), the first and perhaps the lone LBV in the central cluster of 30 Doradus, and only the sixth known LMC LBV. Photometric and spectroscopic observations over the past 40 yr indicate that during that time R143 moved redward (changing from an F5 to F8 supergia…
Ultraviolet Spectroscopy of Herbig-Haro Objects: Spatial Structure, Spectroscopic Diagnostics, and Variability
Noriega-Crespo, A.; Boehm, K. -H.; Solf, J.
Using new long-exposure (two-shift) SWP IUE spectra of HH 2G, (HH 2H + HH 2A'), and HH 1F and archival spectra of (HH 2H + HH 2A') and of HH 1 we have obtained the following results:
1. For the first time we have determined a separate UV spectrum of the high-excitation condensation HH 2G. The spectrum shows similarity to that of HH 2R. Howeve…The Distant Future of Solar Activity: A Case Study of beta Hydri. II. Chromospheric Activity and Variability
Gahm, G. F.; Fredga, K.; Linde, P. +1 more
A detailed comparison of the present sun with the very old star Beta Hyi (G2 IV) is presented in order to study the secular evolution of solar-type chromospheres, with emphasis placed on chromospheric features and their time variability. High-resolution Ca II H and K profiles show the emission to be about half that for the sun, but with the same s…
The Abundances of the Elements in Sharp-lined Early-Type Stars from IUE High-Dispersion Spectrograms. I. Cr, Mn, Fe, Ni, and CO
Adelman, Saul J.; Wahlgren, Glenn M.; Leckrone, David S. +2 more
The current study was undertaken to test the viability of lUE archives as a source of information on elemental species unavailable from (ground-based) coudé spectra. The first step in this endeavor is to check the consistency of abundances obtained from lUE material and those derived from the ground especially as reported in a series of papers by …