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Multiwavelength Observations of the Soft Gamma Repeater SGR 1900+14 during Its 2001 April Activation
Hurley, K.; Kouveliotou, C.; Fender, R. P. +6 more
The soft gamma repeater SGR 1900+14 became active on 2001 April 18 after about 2 years of quiescence; it had remained at a very low state of activity since the fall of 1998, when it exhibited extraordinary flaring. We have observed the source in the gamma-rays and X-rays with Ulysses and Chandra and in the radio with MERLIN. We report here the con…
On the Relationship between He II λ304 Prominences and the Photospheric Magnetic Field
Wang, Y. -M.
As observed in He II λ304 images recorded at high cadence, quiescent prominences resemble long-lived systems of jets, in which chromospheric material streams continually from one footpoint area to another. To further clarify the physical nature of the source regions, we have compared He II λ304 images of on-disk prominences (filaments) with line-o…
High Spectral and Spatial Resolution Observations of Shocked Molecular Hydrogen at the Galactic Center
Yusef-Zadeh, F.; Burton, M.; Wardle, M. +2 more
The presence of OH (1720 MHz) masers and the absence of counterparts at 1665/1667 MHz has proved to be a clear diagnostic of shocked molecular gas associated with Galactic supernova remnants. This suggests that shocked molecular gas should be associated with the OH (1720 MHz) masers that have been detected in the circumnuclear disk (CND) and Sgr A…
Solar Polar Plume Lifetime and Coronal Hole Expansion: Determination from Long-Term Observations
Llebaria, A.; Lamy, P. L.; DeForest, C. E.
We have generated off-limb polar synoptic charts of polar plume evolution at various solar altitudes using EUV Imaging Telescope and Large Angle and Spectrometric Coronagraph data from 1996 December. The charts allow direct measurement of the altitude expansion of the solar minimum coronal holes. We find expansion values that are consistent with t…
On the Nature of Magnetic Shadows in the Solar Chromosphere
Judge, P. G.; McIntosh, S. W.
Recent multi-instrument spacecraft studies of the solar photosphere and chromosphere have uncovered a feature-a ``magnetic shadow''-not previously discussed in the literature. A region of the midchromosphere neighboring, but not within, a network magnetic element exhibits a suppression of both the mean UV line/continuum intensity and the character…
Unidentified Infrared Emission Bands in the Diffuse Interstellar Medium
Okumura, K.; Nakagawa, T.; Onaka, T. +7 more
Using the mid-infrared spectrometer on board the Infrared Telescope in Space and the low-resolution grating spectrometer (PHT-S) on board the Infrared Space Observatory, we obtained 820 mid-infrared (5-12 µm) spectra of the diffuse interstellar medium (DIM) in the Galactic center, W51, and Carina Nebula regions. These spectra indicate that t…
Observational Tests and Predictive Stellar Evolution
Liebert, James; Mamajek, E. E.; Arnett, David +1 more
We compare 18 binary systems with precisely determined radii and masses from 23 to 1.1 Msolar and stellar evolution models produced with our newly revised code TYCHO. ``Overshooting'' and rotational mixing were suppressed in order to establish a baseline for isolating these and other hydrodynamic effects. Acceptable coeval fits are foun…
Detection of Coronal Mass Ejections in V471 Tauri with the Hubble Space Telescope
Bond, Howard E.; Sion, Edward M.; Mullan, D. J. +1 more
V471 Tauri, an eclipsing system consisting of a hot DA white dwarf (WD) and a dK2 companion in a 12.5 hr orbit, is the prototype of the precataclysmic binaries. The late-type component is magnetically active, due to its being constrained to rotate synchronously with the short orbital period. During a program of ultraviolet spectroscopy of V471 Tau…
Distant Cluster Hunting: A Comparison Between the Optical and X-Ray Luminosity Functions from an Optical/X-Ray Joint Survey
Dickinson, Mark; Mack, Jennifer; Donahue, Megan +6 more
We present a comparison of X-ray and optical luminosities and luminosity functions of cluster candidates from a joint optical/X-ray survey, the ROSAT Optical X-Ray Survey. Completely independent X-ray and optical catalogs of 23 ROSAT fields (4.8 deg2) were created by a matched-filter optical algorithm and by a wavelet technique in the X…
Infrared Properties of Weak Radio Sources in the ρ Ophiuchi Molecular Cloud
André, Philippe; Greene, Thomas P.; Wilking, Bruce A. +2 more
We report mid-infrared ISOCAM observations for a sample of radio continuum sources in the ρ Ophiuchi molecular cloud core with unknown or poorly studied infrared counterparts. These data are combined with existing infrared photometry, including recently published ISOCAM data, for previously studied radio sources to investigate the evolutionary sta…