Search Publications
Metal-Line Blanketing and the Peculiar H beta Line Profile in the DAO Star Feige 55
Chayer, P.; Bergeron, P.; Wesemael, F. +1 more
A detailed analysis of the optical spectrum of the DAO white dwarf Feige 55 is presented. We show that the atmospheric parameters obtained from fits to the H-beta line and to higher Balmer lines, respectively, are discrepant. This problem is akin to that reported in previous analyses of hot DAO central stars of planetary nebulae. Model atmosphere …
Ultraviolet Continuum Variability and Visual Flickering in the Peculiar Object MWC 560
Sonneborn, G.; Michalitsianos, A. G.; Shore, S. N. +8 more
High-speed U-band photometry of the peculiar emission object MWC 560 obtained with the ground-based instrumentation, and V-band photometry obtained with the International Ultraviolet Explorer-Fine Error Sensor indicates irregular brightness variations are quasi-periodic. Multiple peaks of relative brightness power indicate statistically significan…
NGC 5018: A Metal-poor Giant Elliptical
Burstein, David; Bertola, Francesco; Buson, Lucio M.
NGC 5018 is a luminous elliptical galaxy with colors and optical absorption-line spectrum similar to those of M32, which is 40 times fainter in luminosity. This giant elliptical is one of the more extreme examples of a minority of elliptical galaxies (perhaps as many as 20%) whose colors are significantly bluer, and Mg_2_ indices significantly wea…
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…