Search Publications
Starbursts and Star Clusters in the Ultraviolet
Leitherer, C.; Garnett, D. R.; Heckman, T. M. +3 more
We present ultraviolet (UV) images of nine starburst galaxies obtained with the Hubble Space Telescope using the Faint Object Camera. The galaxies range in morphology from blue compact dwarfs to ultraluminous merging far-infrared galaxies. Our data combined with new and archival UV spectroscopy and far-infrared fluxes allow us to dissect the anato…
The IUE Survey for Damped Lyman- alpha and Lyman-Limit Absorption Systems: Evolution of the Gaseous Content of the Universe
Turnshek, David A.; Lanzetta, Kenneth M.; Wolfe, Arthur M.
We present a spectroscopic survey for moderate-redshift absorption features from damped Lyα and Lyman- limit absorption systems. The survey is based on a set of optimally extracted and co-added International Ultraviolet Explorer spectra of QSOs, BL Lac objects, and Seyfert galaxies. Results of this survey are combined with those of previous survey…
Software for the Analysis of Emission Line Nebulae
Shaw, Richard A.; Dufour, Reginald J.
A set of software tools has been developed for the IRAF/STSDAS environment to derive the physical conditions in a low-density (nebular) gas given appropriate diagnostic emission line ratios; and lien emissivities given appropriate emission line fluxes, the electron temperature (T_e) and density (N_e). The package is based on the five-level program…
Optical and Ultraviolet Analyses of ZZ Ceti Stars and Study of the Atmospheric Convective Efficiency in DA White Dwarfs
Fontaine, G.; Bergeron, P.; Wesemael, F. +3 more
New high signal-to-noise optical spectrophotometry is presented for 22 ZZ Ceti stars. The atmospheric parameters (Teff log g) and the mass are derived for each object using new model atmospheres and synthetic spectra calculated within the mixing-length theory, as well as recent published mass-radius relationships. Various parameterizati…
Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. VIII. an Intensive HST, IUE, and Ground-based Study of NGC 5548
Veilleux, S.; Shull, J. M.; Malkan, M. A. +109 more
We present the data and initial results from a combined HST/IUE/groundbased spectroscopic monitoring campaign on the Seyfert 1 galaxy NGC 5548 that was undertaken in order to address questions that require both higher temporal resolution and higher signal-to-noise ratios than were obtained in our previous multiwavelength monitoring of this galaxy …
Ultraviolet Radiation from Evolved Stellar Populations. II. The Ultraviolet Upturn Phenomenon in Elliptical Galaxies
O'Connell, Robert W.; Dorman, Ben; Rood, Robert T.
We discuss the far-ultraviolet upturn phenomenon (UVX) observed in elliptical galaxies and spiral galaxy bulges. Our premise is the the UV radiation from these systems emanates primarily from extreme horizontal branch (EHB) stars and their progeny. Such objects have zero-age horizontal branch envelope masses M_env_^0^<~0.05 M_sun_. Local exampl…
Spectral Classification of Galaxies: an Orthogonal Approach
Calzetti, D.; Kinney, A. L.; Connolly, A. J. +2 more
Classification of galaxy spectral energy distributions in terms of orthogonal basis functions provides an objective means of estimating the number of significant spectral components that comprise a particular galaxy type. We apply the Karhunen-Loeve transform to derive a spectral eigensystem from a sample of ten galaxy spectral energy distribution…
Radiative Levitation in Hot White Dwarfs: Equilibrium Theory
Chayer, P.; Fontaine, G.; Wesemael, F.
We present the results of detailed calculations of radiative levitation in hot white dwarfs using the extensive and homogeneous atomic data given in TOPBASE. Radiative accelerations and equilibrium abundances have been computed for C, N, O, Ne, Na, Mg, Al, Si, S, Ar, Ca, and Fe on grids of pure hydrogen and pure helium stellar envelope models. The…
A new model for the infrared emission of quasars
Rowan-Robinson, Michael
The optical-UV continua of 75 PG quasars are modelled to test two extreme hypotheses: (a) the range of continuum shapes observed is the result of different amounts of reddening of a single underlying continuum, and (b) the range of continuum slopes is entirely intrinsic, due to accretion discs being viewed at different inclinations. Although (a) i…
Multiwavelength Observations of Markarian 421 During a TeV/X-Ray Flare
Kafatos, M.; Takahashi, T.; Kondo, Y. +38 more
A TeV flare from the BL Lac object Mrk 421 was detected in May of 1994 by the Whipple Observatory air Cherenkov experiment during which the flux above 250 GeV increased by nearly an order of magnitude over a 2-day period. Contemporaneous observations by ASCA showed the X-ray flux to be in a very high state. We present these results, combined with …