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The Chemical Evolution of the Galactic Disk - Part One - Analysis and Results

Gustafsson, B.; Andersen, J.; Lambert, D. L. +3 more

The ultraviolet to soft X-ray bump of Seyfert 1 type active galactic nuclei.

Walter, R.; Fink, H. H.

The soft X-ray (0.1 - 2.4 keV) emission of 58 Seyfert type active galactic nuclei have been studied using the spectra obtained during the ROSAT all sky survey. These spectra are well represented by power law models with photon indices ranging between 1.6 and 3.4. The spectra usually do not show intrinsic absorption. A notable exception is Mrk 766 …

An Atlas of Ultraviolet Spectra of Star-forming Galaxies

Panagia, N.; Calzetti, D.; Wyse, Rosemary F. G. +2 more

An atlas of ultraviolet spectra of the central regions of 143 spiral, irregular, blue compact, Seyfert 2, and starburst galaxies is produced by combining 387 low-resolution spectra from the IUE data archives. The spectra have been extracted with an optimal algorithm and co-added to produce spectra with the best possible signal-to-noise ratio. Our …

SN 1991bg: A Type IA Supernova With a Difference

Suntzeff, N. B.; Walker, A. R.; Caldwell, Nelson +28 more

We present 13 spectra and 31 photometric observations covering the first 150 days of SN 1991bg in NGC 4374 (M 84). Although SN 1991bg was a type Ia supernova displaying the characteristic Si II absorption at 6150 A near maximum and the Fe emission lines at late phases, it varied from the well-defined norm for SNe Ia in several important respects. …

Elemental abundances in normal late-B and HgMn stars from co-added IUE spectra. I. Iron-peak elements.

Dworetsky, M. M.; Smith, K. C.

The abundances of five iron-peak elements (chromium through nickel) in a sample of forty normal, superficially normal, and HgMn-type late-B stars are derived by spectrum-synthesis analysis of co-added high-resolution International Ultraviolet Explorer (IUE) spectra. Approximately solar abundances of these elements are obtained for the normal stars…

SN 1992A: Ultraviolet and Optical Studies Based on HST, IUE, and CTIO Observations

Suntzeff, N. B.; Fransson, Claes; Challis, Peter M. +18 more

The Type Ia supernova SN 1992A in the 50 galaxy NGC 1380 was observed as a target of opportunity by the International Ultraviolet Explorer (IUE) and with great alacrity by the Hubble Space Telescope (HST). Here we present the HST and lUE spectra and photometry that we obtained, as well as optical spectra obtained at the Cerro Tololo Inter-American…

Stellar Kinematic Groups. I. The URSA Major Group

Soderblom, David R.; Mayor, Michel

The Ursa Major Group (UMaG) is studied as a test case for the authenticity of Stellar Kinematic Groups, using Coravel radial velocities, recent compilations of astrometric data, and new spectroscopic observations. Spectroscopic age indicators, particularly indices of the strength of chromospheric emission, are applied to solar-type candidate membe…

Lithium and Rapid Rotation in Chromospherically Active Single Giants

Fekel, Francis C.; Balachandran, Suchitra

The rotational velocities presently obtained via spectroscopic observations of a group of moderately rapidly rotating, chomospherically active single giants indicate that Gray's (1989) rotostat hypothesis requires modification. Their rapid rotation appears to be due to high Li abundances, and results in increased chromospheric activity. A scenario…

Ultraviolet Spectra of QSOs, BL Lacertae Objects, and Seyfert Galaxies

Turnshek, David A.; Lanzetta, Kenneth M.; Sandoval, Jennifer

Motivated by the possibility of detecting strong absorption features toward extragalactic background objects, we present optimally extracted and co-added IUE spectra of QSOs, BL Lac objects, and Seyfert galaxies. These spectra together with those presented (in a similar work) by Kinney et al. form an essentially complete sample of the SWP, LWP, an…

Multiwavelength Monitoring of the BL Lacertae Object PKS 2155-304. I. The IUE Campaign

Maraschi, L.; Chiappetti, L.; Tagliaferri, G. +26 more

Daily monitoring of PKS 2155 - 304 with the IUE satellite throughout 1991 November has revealed dramatic, large-amplitude, rapid variations in the ultraviolet flux of this BL Lac object. Many smaller, rapid flares are superposed on a general doubling of the intensity. During the 5^d^ period when sampling was roughly continuous, the rapid flaring h…