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New constraints on the cosmic mid-infrared background using TeV gamma-ray astronomy
Lagache, G.; Puget, J. -L.; Renault, C. +1 more
Very high energy gamma-ray data obtained by CAT and HEGRA from the active galactic nucleus Mkn 501 are used to constrain the cosmic Mid-Infrared background. While the entire infrared and submillimeter spectrum shape based on models has been fixed and the density scaled as a whole in previous studies, recent measures on the low and high energy infr…
Properties of Solar Polar Coronal Hole Plasmas Observed above the Limb
Wilhelm, K.; Schühle, U.; Doschek, G. A. +2 more
We determine the line-of-sight emission measure distribution and nonthermal motions as a function of height above the limb in the north and south polar coronal holes. These quantities are derived from extreme-ultraviolet (EUV) spectra obtained from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Helios…
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…
Spectroscopic monitoring of 10 new northern slowly pulsating B star candidates discovered from the HIPPARCOS mission
Mathias, P.; Aerts, C.; Cuypers, J. +4 more
A one-year follow-up campaign of high-resolution, high-signal-to-noise spectroscopy for 10 candidate slowly pulsating B stars, which were discovered from the HIPPARCOS astrometric mission, shows that all stars exhibit line-profile variability. From our data, and from the HIPPARCOS photometry, we conclude that all but one of the targets provide evi…
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…
Statistical Properties of Ultraluminous IRAS Galaxies from an HST Imaging Survey
Mao, S.; Cui, J.; Xia, X. -Y. +2 more
We perform photometric measurements on a large HST snapshot imaging survey sample of 97 ultraluminous infrared galaxies (ULIRGs). We select putative nuclei from bright clumps in all the sample targets, mainly based on a quantitative criterion of I-band luminosity as well as the global and local morphological information. All the sources are then c…
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…