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Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations
Lindegren, Lennart; Madsen, Søren; Dravins, Dainis
Radial motions of stars in nearby moving clusters are determined from accurate proper motions and trigonometric parallaxes, without any use of spectroscopy. Assuming that cluster members share the same velocity vector (apart from a random dispersion), we apply a maximum-likelihood method on astrometric data from Hipparcos to compute radial and spa…
Infrared Views of the TW Hydra Disk
Zuckerman, B.; Schneider, G.; Hines, D. C. +6 more
The face-on disk around TW Hya is imaged in scattered light at 1.1 and 1.6 µm using the coronagraph in the Near Infrared Camera and Multi Object Spectrometer aboard the Hubble Space Telescope. Stellar light scattered from the optically thick dust disk is seen from 20 to 230 AU. The surface brightness declines as a power law of r-2.6+/-0…
The Local Lyα Forest. III. Relationship between Lyα Absorbers and Galaxies, Voids, and Superclusters
Shull, J. Michael; Stocke, John T.; Penton, Steven V.
In this paper we use large-angle, nearby galaxy redshift surveys to investigate the relationship between the 81 low-redshift Lyα absorbers in our Hubble Space Telescope GHRS survey and galaxies, superclusters, and voids. In a subsample of 46 Lyα absorbers located in regions where the 2000 February 8 CfA catalog is complete down to at least L* gala…
Spiral Galaxies with HST/NICMOS. I. Nuclear Morphologies, Color Maps, and Distinct Nuclei
Stiavelli, Massimo; de Zeeuw, P. Tim; Carollo, C. Marcella +2 more
This is the first of two papers where we present the analysis of an HST/NICMOS2 near-infrared (NIR) snapshot survey in the F160W (H) filter for a sample of 78 spiral galaxies selected from the UGC and ESOLV catalogs. For 69 of these objects we provide nuclear color information derived by combining the H data either with additional NICMOS F110W (J)…
The Stellar Velocity Dispersion of the Lens Galaxy in MG 2016+112 at z=1.004
Treu, Tommaso; Koopmans, Léon V. E.
We present a direct measurement of the stellar velocity dispersion of the early-type lens galaxy D in the system MG 2016+112 (z=1.004), determined from a spectrum obtained with the Echelle Spectrograph and Imager on the W. M. Keck II Telescope, as part of the Lenses Structure and Dynamics Survey. We find a velocity dispersion of σap=304…
Chandra observations of RX J1347.5-1145: the distribution of mass in the most X-ray-luminous galaxy cluster known
Fabian, A. C.; Allen, S. W.; Schmidt, R. W.
We present Chandra observations of RX J1347.5-1145, the most X-ray-luminous cluster of galaxies known. We report the discovery of a region of relatively hot, bright X-ray emission, located approximately 20 arcsec to the south-east of the main X-ray peak at a position consistent with the region of enhanced Sunyaev-Zel'dovich effect reported recentl…
Chandra Observations of the Lensing Cluster EMSS 1358+6245: Implications for Self-interacting Dark Matter
Garmire, G. P.; Bautz, M. W.; Arabadjis, J. S.
We present Chandra observations of EMSS 1358+6245, a relaxed cooling flow cluster of galaxies at z=0.328. We employ a new deprojection technique to construct temperature, gas, and dark matter profiles. We confirm the presence of cool gas in the cluster core, and our deprojected temperature profile for the hot component is isothermal over 30kpc<…
Energy Distribution of Microevents in the Quiet Solar Corona
Krucker, Säm; Benz, Arnold O.
Recent imaging observations of EUV line emissions have shown evidence for frequent flarelike events in a majority of the pixels in quiet regions of the solar corona. The changes in coronal emission measure indicate impulsive heating of new material to coronal temperatures. These heating or evaporation events are candidate signatures of ``nanoflare…
Variability of magnetospheric storms driven by different solar wind perturbations
Koskinen, Hannu E. J.; Schwenn, Rainer; Huttunen, K. Emilia J.
We have investigated the solar wind drivers of magnetic storms during the rising phase of solar cycle 23 from January 1996 to December 1999. We used observations of coronal mass ejections (CMEs) by the Large Angle and Spectrometric Coronagraph instrument on SOHO and in situ solar wind observations by Wind, IMP 8, and ACE spacecraft. The storms wer…
Flare waves observed in Helium I 10 830 Å. A link between Hα Moreton and EIT waves
Vršnak, B.; Hanslmeier, A.; Warmuth, A. +1 more
Three traveling disturbances recorded in the absorption line of Helium I at 10 830 Å, (He I), analogous to Hα Moreton waves, are analyzed. The morphology and kinematics of the wavefronts are described in detail. The He I wave appears as an expanding arc of increased absorption roughly corresponding to the Hα disturbance, although not as sharply de…