Search Publications
Multiwavelength Studies of Hercules X-1 during Short High and Anomalous Low States: On-again, Off-again
McCray, R.; O'Brien, K.; Boroson, B. +4 more
We present results from multiwavelength observations of the Hercules X-1 system during a short high state (SHS) and during an anomalous low state (ALS). The magnitude of deviation from spin-up appears to be positively correlated with duration of the ALS. Such a correlation is consistent with an interpretation of the ALS in terms of a change in mas…
Optical Identification of the X-Ray Burster in the Globular Cluster NGC 1851
Anderson, Scott F.; Margon, Bruce; Deutsch, Eric W. +2 more
We have obtained exposures of the field of X0512-401 in the globular cluster NGC 1851, in X-rays with the Chandra X-Ray Observatory, and in the far-UV with the Hubble Space Telescope. We derive an accurate new X-ray position (within ~1") for X0512-401, which enables us to confirm that the only plausible candidate for the optical/UV counterpart is …
Search for Evidence of Alpha-Particle Beams during a Solar Flare Observed by the Coronal Diagnostic Spectrometer aboard the Solar and Heliospheric Observatory
Brosius, Jeffrey W.
We observed NOAA Active Region 9090 (N13°, W39°) with the Coronal Diagnostic Spectrometer (CDS) and the Extreme-Ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory spacecraft between 18:17 and 21:09 UT on 2000 July 24 to search for evidence of alpha-particle beams during solar flares. Theoretically, an alpha-particle …
Discovery of Associated Absorption Lines in an X-Ray Warm Absorber:Hubble Space Telescope Faint Object Spectrograph Observations of MR 2251-178
Elvis, Martin; Mathur, Smita; Wilkes, Belinda +1 more
The presence of a ``warm absorber'' was first suggested to explain spectral variability in an X-ray spectrum of the radio-quiet quasi-stellar object (QSO) MR 2251-178. A unified picture, in which X-ray warm absorbers and ``intrinsic'' UV absorbers are the same, offers the opportunity to probe the nuclear environment of active galactic nuclei. To t…
Optical-Near-Infrared Color Gradients in Early-Type Galaxies at z<=1.0
Hinkley, Sasha; Im, Myungshin
Recent studies based on line indices of nearby early-type galaxies suggest that stars in the galaxies' inner part may be younger and more metal-rich than stars in the outer part. If confirmed, the finding has a profound implication for the formation and evolution of early-type galaxies, since such age gradients naturally arise if merging played an…
A Comparative Study of the Atmospheric Composition of the DA White Dwarfs Feige 24 and G191-B2B
Vennes, Stéphane; Lanz, Thierry
We analyze Hubble Space Telescope Imaging Spectrograph spectra of two white dwarfs, Feige 24 and G191-B2B, and we compare the measured abundance patterns. Except for carbon, which appears overabundant in G191-B2B by 0.3-0.5 dex relative to Feige 24, the average heavy-element abundance in Feige 24 is 0.17 dex larger than in the cooler, hence older,…
Hubble Space Telescope Observations of the Gravitationally Lensed Cloverleaf Broad Absorption Line QSO H1413+1143: Imaging Polarimetry and Evidence for Microlensing of a Scattering Region
Turnshek, David A.; Rao, Sandhya M.; Schulte-Ladbeck, Regina E. +2 more
We report the results of Hubble Space Telescope Wide Field and Planetary Camera 2 broadband F555W and F702W photometric and F555W polarimetric observations of the ``Cloverleaf'' QSO H1413+1143. This is a four-component gravitationally-lensed broad absorption line (BAL) QSO. Observations were obtained at two epochs in 1999 March and 1999 June separ…
Dynamical Cycles in Charge and Energy for Iron Ions Accelerated in a Hot Plasma
Torsti, J.; Kocharov, L.; Kovaltsov, G. A.
We consider a unified model of Fe ion acceleration in the solar corona. The model comprises charge-changing processes, Coulomb energy losses, and both regular and stochastic acceleration. At a given acceleration scenario, the type of acceleration is found to have a minor effect on the mean charge states, but the shapes of the charge-state distribu…
LB 8827: A Variable, Magnetic DBA White Dwarf
Fontaine, G.; Bergeron, P.; Wesemael, F. +3 more
We present accurate CCD spectropolarimetry and spectra that show that the hot DB star LB 8827 (PG 0853+164) is a weakly magnetic, variable DBA white dwarf. We confirm Putney's detection of circular dichroism in the He I lines, but on three occasions we measure a weaker field strength and opposite sign of circular polarization, Be<~10…
Electron Densities, Radial and Terminal Wind Velocities for the Planetary Nebula NGC 6302 and Its O VI-Type Binary Nucleus
Feibelman, Walter A.
Archival high- and low-dispersion IUE spectra of NGC 6302 and its nucleus have been analyzed. The spectra in the NEWSIPS format reveal many high-excitation emission features, including stellar O V, O VI, O VII, and O VIII that identify the nucleus as a new member of the ``O VI sequence.'' Fe II features that are resonantly excited by O VI λ1032 ar…