Search Publications
Hubble Space Telescope Counts of Elliptical Galaxies: Constraints on Cosmological Models?
Driver, Simon P.; Windhorst, Rogier A.; Phillipps, Steven +1 more
The interpretation of galaxy number counts in terms of cosmological models is fraught with difficulty because of uncertainties in the overall galaxy population (mix of morphological types, luminosity functions, etc.) and in the observations (loss of low surface brightness images, image blending, etc.). Many of these can be overcome if we use deep …
Luminosity Evolution in Cluster Galaxies From z=0.41 to z=0.02
Barrientos, L. Felipe; Schade, David; Lopez-Cruz, Omar
HST archive images of the cluster CL 0939+4713 (z = 0.41), together with ground-based images of Coma (z = 0.02), have been used to make a direct comparison of the structural properties of the early-type galaxies in these clusters. This well-matched pair of images has similar rest-frame filter passband, nearly identical resolution in physical units…
A Possible X-Ray Counterpart to SGR 1900+14
Hurley, K.; Kouveliotou, C.; Bowyer, S. +9 more
The location of the soft gamma repeater SGR 1900+14 was recently reduced to two ~5 arcmin2 alternate error boxes by the network synthesis method. We have used the ROSAT High Resolution Imager to observe the error box that is closest to the supernova remnant G42.8+0.6. A quiescent, steady, point X-ray source was found at alpha (2000) = 19h07m14.s15…
Coronal Gas in the Halo. II. ORFEUS Observations of Galactic Halo Stars
Hurwitz, M.; Bowyer, S.
We present new intermediate-resolution spectra (λ/Δλ = 3300) of fourteen early-type halo stars near the O VI resonance doublet at 1031.93 and 1037.62 These spectra were obtained with the Berkeley extreme and far-ultraviolet (EUV/FUV) spectrometer in the ORFEUS telescope aboard the space platform ASTRO-SPAS during the mission of space shuttle Disco…
HST/GHRS Observations of the beta Pictoris System. II. Exploring the Potential for Tracking Comet-like Objects Orbiting the Star
Hubeny, Ivan; Heap, Sara R.
We present a systematic study of the transient absorption features observed in the spectra of β Pictoris. We calculate detailed synthetic spectra of a star, which is partially obscured by a permanent circumstellar disk and by an absorbing body of a given size, position, radial velocity with respect to the star, and total column density. We show th…
Discovery of Photospheric Helium in the Ultra-Massive DA White Dwarf GD 50
Bowyer, Stuart; Vennes, Stephane; Dupuis, Jean
Extreme-ultraviolet (EUV) spectroscopy of the hot, hydrogen-rich white dwarf GD 50 reveals an unusual photospheric mixture of hydrogen and helium. This hot DA white dwarf is also remarkable for its mass (~1.2 M⊙) near the Chandrasekhar limit. The spectra obtained with the Extreme-Ultraviolet Explorer (EUVE) show a prominent He II resonance line se…
Hubble Space Telescope Spectroscopic Observations of the Ejecta of SN 1987A at 2000 Days
Filippenko, Alexei V.; Fransson, Claes; Challis, Peter M. +6 more
We have used the Faint Object Spectrograph on the Hubble Space Telescope (HST) to observe the spectra of SN 1987A over the wavelength range 2000-8000 A on dates 1862 and 2210 days after the supernova outburst. Even these preCOSTAR observations avoid much of the contamination from the bright stars nearby and provide a very useful set of line streng…
The Broadband Energy Distribution of the Misaligned Gamma-Ray Blazar PKS 0521-365
Maraschi, L.; Ghisellini, G.; Pian, E. +4 more
Simultaneous UV and X-ray observations of the blazar PKS 0521-365 are combined with radio, IR, optical, and y-ray data taken at different epochs to study the overall emission from 10 to 1023 Hz. The flux distribution declines from the IR to the UV range (alpha0pt uv = 1.4 + 0.1), but hardens at higher frequencies. The remarkably flat X-…
Abundance and Isotopic Anomalies of Thallium in the Atmosphere of the HgMn Star χ LUPI
Johansson, Sveneric; Wahlgren, Glenn M.; Proffitt, Charles R. +3 more
We announce the detection of two fully resolved hyperfine components of the intercombination line of Tl II (Z = 81) at 1908.6 Å in the ultraviolet spectrum of the sharp-lined, nonmagnetic, chemically peculiar star χ Lupi (B9.5pHgMn + A2 Vm). The wavelengths and profiles of these absorption lines strongly suggest that they arise from the heaviest i…
Hubble Space Telescope Time-resolved Ultraviolet Spectroscopy of ST Leonis Minoris and UZ Fornacis: Resolving the Accretion Stream
Schmidt, Gary D.; Stockman, H. S.
Time-resolved, low-resolution ultraviolet spectroscopy of the magnetic cataclysmic variables ST LMi and UZ For was obtained with the Hubble Space Telescope during periods near eclipse and self-eclipse egress, respectively. The UZ For data indicate three eclipsing components: the white dwarf; a hot, presumably photo spheric emission region on the w…