Search Publications
The Isolated Massive DA White Dwarf GD 50
Bergeron, P.; Wesemael, F.; Holberg, J. B. +3 more
Analysis of accurate hydrogen line profiles from optical and ultraviolet spectrophotometry shows that the hot DA white dwarf GD 50 (WD 0346-011) has an exceptionally high surface gravity of log g = 9.0 + or - 0.15; the derived parameters imply a mass of 1.2 solar mass and a radius of 0.0057 solar mass, if an interior composed of carbon and oxygen …
Persistence and Change in the Soft X-Ray Spectrum of the Quasar PG 1211+143
Elvis, Martin; Wilkes, Belinda J.; Giommi, P. +1 more
Two Einstein and three EXOSAT observations of PG 1211 + 143 over a 6 year baseline show that strong steep-spectrum low-energy X-ray emission is a persistent feature of this quasar. EXOSAT observations of PG 1211 + 143 detected a factor of 2.3 increase in its steep soft X-ray (C-band) flux in 18 days. The bulk of the soft X-ray emission of PG 1211 …
IUE Observations of NGC 5548, 1978--1988: The Sizes and Kinematics of the Broad-Line Region
Gaskell, C. M.; Koratkar, Anuradha P.
We have reextracted the IUE spectra of NGC 5548 taken between 1978 and 1988 and studied changes in the UV continuum flux and UV line intensities. We have used the cross-correlation method advocated by Gaskell & Sparke and refined by Gaskell & Peterson to investigate the structure and kinematics of the broadline region (BLR). We give an ext…
The Shape of the Ultraviolet Continuum of Quasars and Intergalactic Dust
Cheng, F. H.; Koratkar, Anuradha P.; Gaskell, C. Martin
We present measurements of the shape of the UV continuum of a large number of quasars. We investigate earlier claims that the near-UV spectral index α_UV_ gets flatter with increasing look-back time. We also investigate the dependence of α_UV_ on luminosity and radio type. The UV spectra of radio-quiet quasars are systematically slightly flatter t…
HST Observations of 3C 66B: A Double-stranded Optical Jet
Boksenberg, A.; Barbieri, C.; Weigelt, G. +17 more
The Faint Object Camera on the HST has imaged the central region of the synchrotron jet in 3C 66B with ultra-high spatial resolutions. The images have an angular resolution of 0.1'', corresponding to a linear scale of about 40 pc. This is a factor of more than 12 better linear resolution than previous optical images and more than 3 times better th…
The Ultraviolet Spectra of Nearby Radio Galaxies
Keel, William C.; Windhorst, Rogier A.
We report new and archival IUE SWP spectra for nine nearby radio galaxies (V < 15 mag), together with optical emission-line data for these galaxies as well as a number of candidates with weaker line emission. We examine both their UV line and continuum properties, as well as their UV and UV-optical line ratios. We find that: 1. Lyα emission is …
First Results from the Goddard High-Resolution Spectrograph: Evidence for Photospheric Microturbulence in Early O Stars: Are Surface Gravities Systematically Underestimated?
Heap, S. R.; Hubeny, I.; Altner, B.
GHRS spectra of two very hot stars provide evidence for the presence of microturbulence in their photospheres. In attempting to reproduce the observed spectra, theoretical models have been built in which the microturbulence is allowed to modify not only the Doppler line widths (classical 'spectroscopic' microturbulence), but also the turbulent pre…
The Ultraviolet Spectrum and Continuum Energy Distribution of the Bright Quasar H1821+643
Filippenko, Alexei V.; Halpern, Jules P.; Kolman, Michiel +1 more
We report on the first UV observations of the bright QSO H1821+643. With V = 14.2 mag and z = 0.297, H1821+643 is the second brightest object in the sky at z > 0.1. The IUE data are combined with new optical spectroscopy, and existing infrared and X-ray data, to reveal a strong optical/UV "big bump," which continues past the Lyman limit in the …
Multifrequency Observations of BL Lacertae in 1988
Kawai, N.; Matsuoka, M.; Chambers, K. C. +27 more
Simultaneous multiwavelength observations of BL Lacertae were performed on two occasions separated by 1 month in 1988 June and July, covering the radio, submillimeter, infrared, optical, ultraviolet, and X- ray wave bands. In the wide-band photon spectra, the X-ray flux lies clearly above the extension of radio-ultraviolet continuum as expected. T…
Observations of Solar Wind Ion Charge Exchange in the Comet Halley Coma
Balsiger, H.; Ip, W. -H.; Goldstein, B. E. +5 more
Giotto Ion Mass Spectrometer/High Energy Range Spectrometer (IMS/HERS) observations of solar wind ions show charge exchange effects and solar wind compositional changes in the coma of Comet Halley. As the comet was approached, the He(2+) to proton density ratio increased from 2.5 percent in the solar wind to about 4 percent about 1 hr before close…