Search Publications
Early-Type Galaxies, Dark Halos, and Gravitational Lensing Statistics
Maoz, Dan; Rix, Hans-Walter
We present calculations of the expected statistics of gravitational lensing of quasars in the Hubble Space Telescope snapshot survey. We first model early-type (elliptical and SO) galaxies using their observed surface brightness profiles and dynamically inferred mass-to-light ratios. Our work improves upon previous calculations, which have general…
Composition of Interstellar Clouds in the Disk and Halo. I. HD 93521
Fitzpatrick, Edward L.; Spitzer, Lyman, Jr.
Interstellar column densities of Fe, S, Si, Mn, and Mg in their dominant ionization state, as well as of C(+) and S(2+), are presently derived from analyses of HST UV observations of the Galactic halo star HD 93521. Ratios of column densities for the dominant species yield approximations of the logarithmic depletion D(X) in the warm, primarily neu…
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…
X-Ray Variability of Active Galactic Nuclei: A Universal Power Spectrum with Luminosity-dependent Amplitude
Papadakis, I.; Lawrence, A.
We present power-law model fits to the power spectra of 12 high- quality "long look" observations of AGNs from the EXOSAT data base. The AGNs concerned differ in X-ray luminosity L_x_, over a range 10^4^. The results are consistent with all objects having a power spectrum index equal to the mean value α = 1.55. There is no correlation with L_x_, s…
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…
Hubble Space Telescope Imaging of the Narrow-Line Region of NGC 4151
Ford, H. C.; Kriss, G. A.; Evans, I. N. +3 more
We have used the Planetary Camera aboard the Hubble Space Telescope to obtain high spatial resolution [O III] λ5007 and Hα λ6563 + [N II] λλ6548, 6583 images of the nucleus of NGC 4151. Almost all of the Hα λ6563 + [N II] λλ6548, 6583 emission arises from an unresolved nuclear point source. The [O III] λ5007 image resolves the narrow-line region i…
The Ionization Cones in the Seyfert Galaxy NGC 5728
Krolik, J. H.; Wilson, A. S.; Heckman, T. M. +2 more
We report high-resolution (0.1") observations of the Seyfert 2 galaxy NGC 5728 with the Hubble Space Telescope. Images have been obtained in the light of [O III] λλ4959, 5007, Hα+[N II] λλ6548, 6583 and green and red continua. The emission-line images reveal a spectacular biconical structure with overall extent 1.8 kpc. The two cones share a commo…
Abundance of Interstellar Carbon toward zeta Ophiuchi
Ebbets, Dennis C.; Savage, Blair D.; Cardelli, Jason A. +1 more
We report on the detection of the weak intersystem transition of semiforbidden C II 2325 A in the sight line toward Zeta Oph using the Ech-B mode of the Goddard High-Resolution Spectrograph. The measured equivalent width of the semiforbidden C II line is W(lambda) = 0.52 +/- 0.12 mA, implying a C II column density of 1.80 (+/- 0.42) x 10 exp 17 at…
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…
The Hubble Space Telescope Snapshot Survey. IV. A Summary of the Search for Gravitationally Lensed Quasars
Gould, A.; Maoz, D.; Meylan, G. +7 more
We report the concluding results of the HST Snapshot Survey for gravitationally lensed quasars. New observations of 153 high-luminosity z > 1 quasars are presented, bringing to 498 the total number of quasars observed in the survey. The new observations do not reveal new candidates for gravitational lensing. We present tables summarizing all of…