Search Publications
Weak Soft X-Ray Excesses Need Not Result from the High-Frequency Tail of the Optical/Ultraviolet Bump in Active Galactic Nuclei
Czerny, Bozena; Zycki, Piotr T.
The broad-band ROSAT/EXOSAT X-ray spectra of six Seyfert 1 galaxies are fitted by a model consisting of a direct power law and a component due to reflection/reprocessing from a partially ionized, optically thick medium. The reflected spectrum contains emission features from various elements in the soft X-ray range. In all objects but one (Mrk 335)…
Properties of the Highly Ionized Disk and Halo Gas toward Two Distant High-Latitude Stars
Sembach, K. R.; Savage, Blair D.
Goddard High Resolution Spectrograph (GHRS) intermediate -resolution observations of S III, Si III, Al III, Si IV, C IV, and N V absorption along the sight lines to HD 18100 (l = 217.9 deg, b = -62.7, d = 3.1 kpc, z = -2.8 kpc) and HD 100340 (l = 258.9 deg, b = +61.2 deg, d = 5.3 kpc, z = 4.6 kpc) are presented. These small science aperture spectr…
Interstellar Detection of the Intersystem Line SI ii] lambda 2335 toward zeta Ophiuchi
Savage, Blair D.; Sofia, Ulysses J.; Cardelli, Jason A. +2 more
We report on the detection of the weak intersystem transistion of Si II lambda 2335 A in the sight line toward zeta Oph using the Ech-B mode (3.5 km/s resolution) of the Goddard High Resolution Spectrograph. The high-quality spectrum is characterized by an empirically measured signal-to-noise of 450, in excellent agreement with that expected from …
The Stellar Population in the Core of M15
Paresce, Francesco; de Marchi, Guido
The inner core of the globular cluster M15 within approximately 2 sec of the geometrical center has been explored with high-resolution images taken through several broad-band UV filter with the Faint Object Camera (FOC) on board the Hubble Space Telescope (HST). Approximately 210 stars in this region down to a 5 sigma detection limit of m220<…
Variable Extinction in HD 45677 and the Evolution of Dust Grains in Pre--Main-Sequence Disks
Sitko, Michael L.; Halbedel, Elaine M.; Lawrence, Geoffrey F. +2 more
Changes in the UV extinction and IR emission were sought in the Herbig Ae/Be star candidate HD 45677 (= FS CMa) by comparing UV, optical, and IR observations made approximately 10 yr apart. HD 45677 varied significantly, becoming more than 50% brighter in the UV and optical than it was a decade ago. A comparison of the observations between epochs …
Remarkable Long-Term Changes in the Small Magellanic Cloud Wolf-Rayet System HD 5980
Koenigsberger, G.; Auer, L. H.; Moffat, A. F. J. +3 more
In this paper we report the remarkable changes which occurred in the Small Magellanic Cloud W-R system HD5980 = AB5 between 1978 and 1991. Within this timescale, there has been a systematic enhancement (by factors of 2-10 depending on the line) in the equivalent widths of all emission lines, and a change in the relative strengths of N III, N IV, a…
Eclipse Mapping of the Accreting Magnetic White Dwarf in DP Leonis with HST
Holberg, J. B.; Liebert, James; Schmidt, Gary D. +1 more
We present time-resolved ultraviolet spectrophotometry of the AM Her system DP Leo (E1114+182), obtained with the Faint Object Spectrograph on the Hubble Space Telescope (HST) in 1991 October. During this period, the binary was in a low-activity state. Complementary optical spectrophotometry and spectopolarimetry were obtained in 1991 October and …
Ultraviolet Interstellar Polarization Observed with the Hubble Space Telescope
Martin, P. G.; Walsh, J. R.; Nandy, K. +9 more
We have used the Faint Object Spectrograph of the Hubble Space Telescope to observe interstellar linear polarization from 1300 to 3300 A in two stars with well-studied interstellar polarization at visible wavelenths. The wavelength dependence of linear polarization declines smoothly with decreasing wavelength and is devoid of structure associated …
Spectral Energy Distributions of the Brightest Palomar-Green Quasars at Intermediate Redshifts
Tripp, Todd M.; Green, Richard F.; Bechtold, Jill
We have combined low-dispersion International Ultraviolet Explorer (IUE) spectra with the optical/near-IR spectrophotometry of Neugebauer et al. (1987) in order to study the spectral energy distributions of seven of the brightest Palomar-Green quasars at intermediate redshifts (0.9 <= z_em_ <= 1.5). Some of these PG quasars are barely detect…
High-Resolution Optical and UV Observations of the Centers of NGC 1316 and NGC 3998 with the Hubble Space Telescope
Fabbiano, G.; Trinchieri, G.; Fassnacht, C.
B and UV high-resolution images obtained with the HST FOC reveal centrally increasing surface brightness and UV-bright point sources at the nuclei of the early-type galaxies NGC 1316 and NGC 3998. Model fitting of the surface brightness distribution does not exclude a central flattening, which could however be the result of extinction and/or of im…