Search Publications
Hubble Space Telescope Observations of Planetary Nebulae in the Magellanic Clouds. I. The Extreme Type I SMP 83/WS 35
Dopita, Michael A.; Ford, Holland C.; Evans, Ian N. +2 more
We have obtained Hubble Space Telescope Planetary Camera images in both the Hα and the [O III] λ5007 emission lines of the planetary nebula SMP 83 alias WS35, alias N66 in the Large Magellanic Cloud. By combining these results with optical and UV spectrophotometry, absolute flux measurements, and dynamical and density information, we have been abl…
A Giant X-Ray Flare on lambda Eridani (B2e)
Smith, Myron A.; Peters, Geraldine J.; Grady, Carol A. +1 more
A 30 ks observation with the ROSAT PSPC distributed over 39 hr shows that the putatively single, mild B2e star Lambda Eri emits at most times a soft X-ray flux at a rate and temperature consistent with other B stars. However, during the middle of our observations, this star's X-ray flux increased by a factor of 6 before returning to the basal leve…
The Ultraviolet Continua of Blazars: A Reconsideration of IUE Archives
Pian, E.; Treves, A.
The IUE archive data on blazars are reconsidered. They refer to 47 objects, 24 radio-strong BL Lac objects, 15 radio-weak BL Lac objects, and eight optically violently variable quasars, increasing substantially the sample examined by Ghisellini et al. (1986). For each object a dereddened spectral slope is evaluated starting from the extraction of …
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…