Search Publications
Time-Series Observations of O Stars. III. IUE and HST Spectroscopy of zeta Ophiuchi and Implications for the ``Photospheric Connection''
Ebbets, D. C.; Bolton, C. T.; Prinja, R. K. +9 more
Stellar-wind variability in the archetypal nonradially pulsating O star ζ Oph (09.5 V) is discussed on the basis of new time-series lUE and HST spectroscopy and archival results. Time-variable "discrete absorption components" are first observed at high velocities (≳ 103 km s-1 ≃ 0.8υ∞) and then migrate blueward; th…
On the Interpretation of the Ultraviolet Spectra of Symbiotic Stars and Recurrent Novae. I.
Shore, Steven N.; Aufdenberg, Jason P.
We present an analysis of high-resolution spectra of several symbiotics and symbiotic novae. We show that the emission lines are severely affected by differential extinction caused by absorption lines in the wind of the red giant companion. The major source of the absorbing spectrum is the forest of lines produced by neutral and singly ionized iro…
Simultaneous ROSAT, GINGA, VLA, IUE, and Optical Observations of the Bright Quasar H1821+643
Filippenko, Alexei V.; Halpern, Jules P.; Fink, Henner H. +3 more
We report on the first simultaneous optical, UV, and X-ray spectroscopy of the low-redshift (z = 0.297), high-luminosity QSO H 1821 + 643. This multiwavelength campaign was complemented by optical imaging and radio mapping with the VLA. Although there was no significant variability during the 40 day monitoring period in either the UV or X-ray band…
Multifrequency Observations of the Optically Active Radio-quiet Quasar GQ Comae. II. Ultraviolet, Optical, and Infrared Continuum Variability
Sitko, Michael L.; Szczerba, R.; Siemiginowska, Aneta +1 more
This paper summarizes the data and preliminary results of a 3 yr long project to monitor the continuum variability of GQ Comae (PG 1202+281) from 0.12 microns to 3.5 microns. Substantial variability in the optical/ultraviolet flux was observed. The variability is examined using a geometrically thin accretion disk model. The model is able to reprod…
Detection of Accreting Gas toward HD 45677: A Newly Recognized, Herbig Be Proto--Planetary System
Grady, C. A.; Perez, M. R.; The, P. S. +4 more
We report the detection of high-velocity, accreting gas toward the BE(e) star with IR excess and bipolar nebula, HD 45677. High-velocity (+200 to +400 km/s), variable column density gas is visible in all IUE spectra from 1979 to 1992 in transitions of Si II, C II, Al III, Fe III, Si IV, and C IV. Low-velocity absorption profiles from low oscillato…
The Hubble Space Telescope Snapshot Survey. III. Further Observations in Search of Gravitationally Lensed Quasars
Maoz, D.; Lahav, O.; Schneider, D. P. +4 more
We present new HST Snapshot Survey observations of 163 high-luminosity z > 1 quasars, bringing the total number observed to date in the survey to 347 quasars. Each exposure was searched for evidence of gravitational lensing. Among the newly observed quasars, six have additional point sources at separations of 2"-6", but in all six cases ground-…
The Circumstellar Gas Surrounding 51 Ophiuchi: A Candidate Proto--Planetary System Similar to beta Pictoris
Grady, C. A.; Silvis, J. M. S.
Combined archival and recent International Ultraviolet Explorer (IUE) observations of the star, 51 Oph, reveal the presence of variable, accreting gas with velocities as large as + 100 km/s relative to the system. The electron number density of the circumstellar gas is comparable to that observed around the candidate proto-planetary system, Beta P…
Ultraviolet Polarimetry and Spectroscopy of the BL Lacertae Object PKS 2155-304
Anderson, Scott F.; Miller, Bryan W.; Smith, Paul S. +3 more
We present ultraviolet spectropolarimetry of the BL Lac object 2155 - 304. These observations were made using the Hubble Space Telescope and the Faint Object Spectrograph and, represent the first opportunity to study the wavelength dependence of the UV (1360-3300 A) linear polarization in a BL Lac object. Nearly simultaneous ground-based optical p…
The Luminosity Dependence of the X-Ray Spectrum of the Transient 42 Second Pulsar EXO 2030+375
Parmar, A. N.; White, N. E.; Reynolds, A. P.
We report on the evolution in the X-ray spectrum of the transient X-ray pulsar EXO 2030 + 375 during part of an outburst in 1985 May-August. The overall continuum spectral shape is similar to that of other accreting pulsars and can be represented by a power-law spectrum modified at low energies by significant absorption and at high energies either…
Implications of the Soft X-Ray versus Hard X-Ray Temporal Relationship in Solar Flares
Mariska, John T.; Li, Peng; Emslie, A. Gordon
We have calculated the time profiles of spatially integrated hard X-ray (30-500 keV) and soft X-ray (1-8 Å) emission in both thick-target electron-heated models, and bulk heated thermal models, of the impulsive phase of solar flares. For the thermal model, we find a serious difficulty: the time profiles of the 30-500 keV hard X-ray emission do not…