Search Publications
Galaxies with Extreme Infrared and Fe II Emission. I. Markarian 231: The Signature of a Young Infrared QSO
Colina, Luis; Macchetto, F.; Lipari, Sebastian
We investigate the ultraluminous IR Galaxy/QSO Mrk 231 by means of long-slit optical spectroscopy, high spatial resolution broad-band optical imaging and UV IUE spectra. The spectrum shows an extreme Fe II optical emission (Fe II_OPT_/Hβ ~ 8), broad Balmer and Na ID lines, weak high-excitation lines, double-peaked optical narrow emission lines wit…
Non--LTE Model Atmosphere Analysis of Nova Cygni 1992
Sonneborn, G.; Hauschildt, P. H.; Shore, S. N. +3 more
We use spherically symmetric non-local thermodynamic equilibrium (non-LTE), line-blanketed, expanding model atmospheres to analyze the International Ultraviolet Explorer (IUE) and optical spectra of Nova Cygni 1992 during the early phases of its outburst. We find that the first IUE spectrum obtained just after discovery on 1992 February 20, is bes…
The Coronal Electron Density Distribution Determined from Dual-Frequency Ranging Measurements during the 1991 Solar Conjunction of the ULYSSES Spacecraft
Bird, M. K.; Asmar, S. W.; Volland, H. +3 more
Dual-frequency ranging and Doppler measurements were conducted in support of the Ulysses Solar Corona Experiment (SCE) at and around the spacecraft's first solar conjunction in 1991 August. The differential group delay time between range codes on the two downlink carrier signals at the wavelengths 13.1 and 3.6 cm, a direct measure of the total ele…
The Discovery of 8.7 Second Pulsations from the Ultrasoft X-Ray Source 4U 0142+61
Mereghetti, S.; Stella, L.; Israel, G. L.
We discovered a periodicity at about 8.7s from the X--ray sources 4U0142+61, previously considered a possible black hole candidate on the basis of its ultrasoft spectrum. The pulsations are visible only in the 1--4 keV energy range, during an observation obtained with the EXOSAT satellite in August 1984. A search for delays in the pulse arrival ti…
Hubble Space Telescope Goddard High-Resolution Spectrograph Observation of U Geminorum during Quiescence: Evidence for a Slowly Rotating White Dwarf
Szkody, Paula; Sion, Edward M.; Long, Knox S. +1 more
We have obtained a pair of consecutive far-ultraviolet Goddard High-Resolution Spectrograph (GHRS) exposures of the Si IV region of the dwarf nova U Geminorum in early quiescence, 8 days after its return to optical quiescence when the underlying white dwarf dominates the ultraviolet light of the system. Our GHRS observation revealed a fully resolv…
Composition of Interstellar Clouds in the Disk and Halo. II. gamma 2 Velorum
Fitzpatrick, Edward L.; Spitzer, Lyman, Jr.
High-resolution observations of gamma2 Vel with the Goddard High-Resolution Spectrograph (GHRS) echelle on the Hubble Space Telescope reveal the presence of seven narrow absorption components, with LSR velocities between -23 and +9 km s-1. Three of these show column density ratios N(S(++))/N(S(+)) and N(P(++))/N(P+)) of about…
The X-Ray Spectra of Blazars Observed with EXOSAT
Giommi, Paolo; Barr, Paul; Sambruna, Rita M. +3 more
A systematic analysis of the X-ray spectra (0.1-10 keV) of all blazars observed with EXOSAT is presented. The objects include 16 X-ray-selected BL Lac objects (XBLs), five radio-selected BL Lac objects (RBLs), and five highly polarized quasars (HPQs). Comparing the results of single-power-law fits for the different classes, we find that XBLs have …
HST Images of Nearby Luminous Quasars
Schneider, Donald P.; Bahcall, John N.; Kirhakos, Sofia
Strong upper limits are placed on the visual-band brightnesses of galactic hosts for four luminous, radio-quiet quasars with redshifts between 0.16 and 0.24 that were studied with the HST's Wide Field/Planetary Camera 2 (WFPC2). Typical upper limits on the luminosities of galactic hosts are ~1.4 mag fainter than L^*^ for spirals and ~0.5 mag faint…
The Early Bolometric Evolution of Nova Cygni 1992
Shore, Steven N.; Sonneborn, George; Starrfield, Sumner +2 more
We report on combined ultraviolet and optical observations of early stages of the outburst of Nova Cygni 1992. We show that the initial optical rise and decline were produced by the dramatic increase in UV line opacity and its gradual subsequent lifting as the ejecta expand. The source of the Mv - t3 relation is easily unders…
The Discovery of NI V in the Photospheres of the Hot DA White Dwarfs RE 2214-492 and G191-B2B
Barstow, M. A.; Sion, E. M.; Holberg, J. B. +3 more
We have co-added six recently obtained International Ultraviolet Explorer (IUE) echelle spectra of the hot DA white dwarf RE 2214-492 and 10 existing archive spectra of the well-known hot DA, G191-B2B. We find that both stars contain numerous weak features due to Ni V. Nickel is thus the second iron-group element to be found in the spectra of the …