Search Publications
Ultraviolet Spectral Morphology of the Stellar Core of eta Carinae
Walborn, Nolan R.; Ebbets, Dennis C.; Parker, Joel Wm.
We present high-quality spectra of eta Car between 1203 and 1765 A obtained with the Goddard High Resolution Spectrograph on board the Hubble Space Telescope. A square entrance slit 0."22 in diameter was used to isolate the brightest region of the core, "component A," from the nearby knots of ejecta and the nebulosity in which it is embedded. The …
Sounding the Sun's Chromosphere
Duvall, T. L., Jr.; Shibahashi, H.; Jefferies, S. M. +3 more
Time-distance analysis of solar acoustic waves with frequencies above the nominal atmospheric acoustic cutoff frequency (~5.3 mHz) shows partial reflection of the waves at both the Sun's photosphere and a layer located higher in the atmosphere. This result supports recent reports of chromospheric modes.
Atomic Data for the Re II UV 1 Multiplet and the Rhenium Abundance in the HgMn-type Star χ Lupi
Wahlgren, Glenn M.; Lawler, J. E.; Leckrone, David S. +5 more
We report new laboratory spectroscopic analyses that have been conducted to acquire wavelength and oscillator strength data for lines of the Re II UV 1 multiplet. Wavelengths were determined to a sub-milliangstrom accuracy for the hyperfine and isotopic structure components from laboratory spectra obtained with the Lund VUV Fourier Transform Spect…
Lyα-induced Fluorescence of H2 and Co in Hubble Space Telescope Spectra of a Comet Shoemaker-Levy 9 Impact Site on Jupiter
Wolven, Brian C.; Feldman, Paul D.; Strobel, Darrell F. +1 more
Far-ultraviolet spectra of Jupiter obtained on 1994 July 20 in the region of the Shoemaker-Levy 9 G-fragment impact site contain features that differ markedly from the typical Jovian dayglow spectrum. These features are identified as fluorescence of H2 due to pumping by solar Lyα photons, which requires the presence of a substantial pop…
On the Nature of the Strong Emission-Line Galaxies in Cluster CL 0024+1654: Are Some the Progenitors of Low-Mass Spheroidals?
Koo, David C.; Gallego, Jesús; Wirth, Gregory D. +1 more
We present new size, line ratio, and velocity width measurements for six strong emission-line galaxies in the galaxy cluster, Cl 0024+1654, at redshift z ~ 0.4. The velocity widths from Keck spectra are all narrow (30 <~ σ <~ 120 km s-1), with three profiles showing double peaks. Four galaxies have low masses (M <~ 1010
Ultraviolet Imaging Observations of the cD Galaxy in Abell 1795: Further Evidence for Massive Star Formation in a Cooling Flow
O'Connell, Robert W.; Bohlin, Ralph C.; Smith, Andrew M. +5 more
We present images from the Ultraviolet Imaging Telescope (UIT) of the Abell 1795 cluster of galaxies. We compare the cD galaxy morphology and photometry of these data with those from existing archival and published data. The addition of a far-UV color helps us to construct and test star formation model scenarios for the sources of UV emission. Mod…
The Absence of Diffuse Gas around the Dwarf Spheroidal Galaxy Leo I
Bowen, David V.; Ferrara, Andrea; Blades, J. Chris +2 more
We have obtained spectra of three QSO/AGNs with the GHRS aboard the Hubble Space Telescope to search for absorption from low column density gas in the halo of the dwarf spheroidal (dSph) galaxy Leo I. The probe sight lines pass 2.1, 3.7, and 8.1 kpc from the center of the galaxy, but no C IV, Si II, or Si IV absorption is found at the velocity of …
Quasar Variability and Gravitational Microlensing
Taylor, A. N.; Hawkins, M. R. S.
In this Letter we examine the claim by Baganoff & Malkan that the timescale of brightness variations of quasars increases with decreasing optical wavelength, and that this effect can offset a time dilation effect at high redshift. They base their case on a thin accretion disk model that implies that timescales become shorter as the observed pa…
Boron Abundances of B Stars of the Orion Association
Gies, Douglas R.; Cunha, Katia; Lambert, David L. +2 more
The boron abundance of four B-type stars from the Orion association has been determined from Goddard High Resolution Spectrograph (GHRS)/Hubble Space Telescope (HST) spectra covering the B II 1362 Å resonance line. After correction for large non-LTE effects, the mean boron abundance is similar to the meteoritic abundance, but a factor of 4 (0.6 de…
Wide Field Planetary Camera 2 Photometry of the Bright, Mysterious White Dwarf Procyon B
Provencal, J. L.; Bergeron, P.; Sion, E. M. +4 more
Procyon B is one of a select group of white dwarf stars which are members of visual binary systems and represents a critically important object for testing the fundamental physics of stellar degeneracy. We have accurate measurements of the binary period and the white dwarf mass. However, the extreme brightness ratio and the small separation betwee…