Search Publications
The NextGen Model Atmosphere Grid for 3000<=Teff<=10,000 K
Baron, E.; Hauschildt, Peter H.; Allard, France
We present our NextGen Model Atmosphere grid for low-mass stars for effective temperatures larger than 3000 K. These LTE models are calculated with the same basic model assumptions and input physics as the VLMS part of the NextGen grid so that the complete grid can be used, e.g., for consistent stellar evolution calculations and for internally con…
Dust Absorption and the Ultraviolet Luminosity Density at z ~ 3 as Calibrated by Local Starburst Galaxies
Heckman, Timothy M.; Meurer, Gerhardt R.; Calzetti, Daniela
We refine a technique to measure the absorption-corrected ultraviolet (UV) luminosity of starburst galaxies using rest-frame UV quantities alone and apply it to Lyman-limit U dropouts at z~3 found in the Hubble Deep Field (HDF). The method is based on an observed correlation between the ratio of far-infrared (FIR) to UV fluxes with spectral slope …
The Ultraviolet and Optical Continuum Emission in Active Galactic Nuclei: The Status of Accretion Disks
Koratkar, Anuradha; Blaes, Omer
A fundamental component of models of active galactic nuclei (AGNs) is an accretion disk around a supermassive black hole. However, the nature of this accretion disk is not well understood, and current models do not provide a satisfactory explanation of the optical/UV continuum observed in AGNs. In this paper we review the substantial theoretical a…
Far-Ultraviolet Radiation from Elliptical Galaxies
O'Connell, Robert W.
Far-ultraviolet radiation is a ubiquitous, if unanticipated, phenomenon in elliptical galaxies and early-type spiral bulges. It is the most variable photometric feature associated with old stellar populations. Recent observational and theoretical evidence shows that it is produced mainly by low-mass, small-envelope, helium-burning stars in extreme…
A Hubble Space Telescope Survey for Resolved Companions of Planetary Nebula Nuclei
Bond, Howard E.; Ciardullo, Robin; Fullton, Laura K. +3 more
We report the results of a Hubble Space Telescope ``snapshot'' survey aimed at finding resolved binary companions of the central stars of Galactic planetary nebulae (PNe). Using the the Wide Field and Planetary Camera and Wide Field Planetary Camera 2, we searched the fields of 113 PNe for stars whose close proximity to the central star suggests a…
A comprehensive study of intense star formation bursts in irregular and compact galaxies
Mas-Hesse, J. Miguel; Kunth, Daniel
We have analyzed the properties of the star formation episodes taking place in a sample of blue compact and irregular galaxies by comparing their multiwavelength observational properties with the predictions of evolutionary population synthesis models. This method has allowed us to constrain the age, star formation regime (instantaneous or extende…
A Reanalysis of the Ultraviolet Extinction from Interstellar Dust in the Large Magellanic Cloud
Gordon, Karl D.; Clayton, Geoffrey C.; Misselt, K. A.
We have reanalyzed the Large Magellanic Cloud's (LMC) ultraviolet (UV) extinction using data from the IUE final archive. Our new analysis takes advantage of the improved signal-to-noise ratio of the IUE NEWSIPS reduction, the exclusion of stars with very low reddening, the careful selection of well-matched comparison stars, and an analysis of the …
The Metagalactic Ionizing Radiation Field at Low Redshift
Shull, J. Michael; Giroux, Mark L.; Penton, Steven V. +2 more
We compute the ionizing radiation field at low redshift, arising from Seyferts, QSOs, and starburst galaxies. This calculation combines recent Seyfert luminosity functions, extrapolated ultraviolet fluxes from our IUE-AGN database, and a new intergalactic opacity model based on Hubble Space Telescope and Keck Lyα absorber surveys. At z=0 for AGNs …
The ISO spectrum of the young star HD 142527
Waters, L. B. F. M.; de Koter, A.; Waelkens, C. +2 more
We present a detailed analysis of SWS (2.35-45 mu m) and LWS (43-200 mu m) spectra obtained with the Infrared Space Observatory (ISO) (Kessler et al. 1996) of the dusty circumstellar disk surrounding the isolated young Fe star HD 142527. Two dust populations can be clearly discriminated: a warm component which is dominated by very strong silicate …
Ultraviolet and Multiwavelength Variability of the Blazar 3C 279: Evidence for Thermal Emission
Maraschi, L.; Chiappetti, L.; Pian, E. +13 more
The γ-ray blazar 3C 279 was monitored on a nearly daily basis with IUE, ROSAT, and EGRET for 3 weeks between 1992 December and 1993 January. During this period, the blazar was at a historical minimum at all wavelengths. Here we present the UV data obtained during this multiwavelength campaign. A maximum UV variation of ~50% is detected, while duri…