Search Publications
Boron in Very Metal Poor Stars
Lambert, David L.; Edvardsson, Bengt; Rebolo, Rafael +3 more
We have observed the B I 2497 A line to derive the boron abundances of two very metal-poor stars selected to help in tracing the origin and evolution of this element in the early Galaxy: BD +23 3130 and HD 84937. The observations were conducted using the Goddard High Resolution Spectrograph on board the Hubble Space Telescope. A very detailed abun…
Hubble Space Telescope WFPC2 Color-Magnitude Diagrams of Halo Globular Clusters in M33: Implications for the Early Formation History of the Local Group
Sarajedini, Ata; Schommer, Robert; Geisler, Doug +1 more
We have constructed color-magnitude diagrams for 10 globular clusters in the halo of the nearby spiral galaxy M33 based on Hubble Space Telescope Wide Field Planetary Camera 2 observations in the F555W (~V) and F814W (~I) filters. These data reveal the morphology of the horizontal branch (HB) and allow us to estimate the cluster metallicity using …
The solar origin of the January 1997 coronal mass ejection, magnetic cloud and geomagnetic storm
St. Cyr, O. C.; Webb, D. F.; Gopalswamy, N. +2 more
The magnetic cloud and geomagnetic storm on January 10-11, 1997 were associated with a halo-type Coronal Mass Ejection (CME) observed by the SOHO/LASCO coronagraphs near the sun on January 6. We summarize the solar activity related to this CME and the subsequent storm at Earth. This solar activity was remarkably weak and unimpressive. If the wide …
Anomalous Cooling of the Massive White Dwarf in U Geminorum Following a Narrow Dwarf Nova Outburst
Szkody, Paula; Sion, Edward M.; Cheng, F. H. +4 more
We obtained Hubble Space Telescope Goddard High-Resolution Spectrograph medium-resolution (G160M grating), phase-resolved spectroscopic observations of the prototype dwarf nova U Geminorum during dwarf nova quiescence, 13 days and 61 days following the end of a narrow outburst. The spectral wavelength ranges were centered on three different line r…
HST/GHRS observations of AM Herculis
Gänsicke, B. T.; Beuermann, K.; Szkody, P. +2 more
We present phase-resolved spectroscopy of AM Herculis obtained with the HST/GHRS when the system was in a high state. The ultraviolet light curve shows a quasi-sinusoidal modulation, which can be explained by a hot spot on the rotating white dwarf. The broad Lyalpha absorption expected for photospheric radiation of a moderately hot white dwarf is …
The Hot Stars of Old Open Clusters: M67, NGC 188, and NGC 6791
O'Connell, Robert W.; Bohlin, Ralph C.; Landsman, Wayne +4 more
We analyze ultraviolet (~1500 Å) images of the old open clusters M67, NGC 188, and NGC 6791 obtained with the Ultraviolet Imaging Telescope (UIT) during the second flight of the Astro observatory in 1995 March. Twenty stars are detected on the UIT image of M67, including 11 blue stragglers, seven white dwarf candidates, and the yellow giant-white …
A Multiwavelength Campaign on γ Cassiopeiae. I. The Case for Surface X-Ray Flaring
Smith, Myron A.; Robinson, Richard D.; Corbet, Robin H. D.
In 1996 March we obtained simultaneous Rossi X-Ray Timing Explorer RXTE Proportional Counter Array (PCA) and Hubble Space Telescope (HST) Goddard High-Resolution Spectrograph (GHRS) light curves for the B0.5e star γ Cas in order to compare its X-ray and ultraviolet continuum flux behaviors. The GHRS data set consisted of a nearly continuous sequen…
The HIPPARCOS Hertzsprung-Russell diagram of S stars: probing nucleosynthesis and dredge-up
Jorissen, A.; Udry, S.; Mayor, M. +2 more
HIPPARCOS trigonometrical parallaxes make it possible to compare the location of Tc-rich and Tc-poor S stars in the Hertzsprung-Russell (HR) diagram: Tc-rich S stars are found to be cooler and intrinsically brighter than Tc-poor S stars. The comparison with the Geneva evolutionary tracks reveals that the line marking the onset of thermal pulses on…
The Infrared Morphology of eta Carinae
Smith, Nathan; Gehrz, Robert D.; Krautter, Joachim
We present results of a recent 2-12 µm ground-based infrared (IR) imaging study of Eta Carinae. We discuss the comparative spatial morphology of the bipolar lobes, the ``skirt'' defined by the equatorial ejecta, and the bright features in the core. We derive separate color temperature values of 200, 240, and 420 K for the bipolar lobes, skir…
Evolution of the Angular Correlation Function
Connolly, A. J.; Szalay, A. S.; Brunner, R. J.
For faint photometric surveys, our ability to quantify the clustering of galaxies has depended on interpreting the angular correlation function as a function of the limiting magnitude of the data. Because of the broad redshift distribution of galaxies at faint magnitude limits, the correlation signal has been extremely difficult to detect and inte…