20,935 research outputs found
HI Clouds detected towards Virgo with the Arecibo Legacy Fast ALFA Survey
The Arecibo Legacy Fast ALFA survey is in the process of yielding a complete
HI dataset of the Virgo Cluster and its environs (Giovanelli et al. 2007, Kent
et al., in preparation). Assuming a distance to Virgo of 16.7 Mpc, the minimum
detectable HI mass by ALFALFA is of order 2 x 10^7 Msun. A number of the HI
detections appear to have interesting properties. Some appear associated with,
but offset from, low surface brightness optical counterparts; others, at larger
spatial offsets, may be tidally related to optical counterparts. Yet another
class includes detections which are not identifiable with any optical
counterparts. We present the ALFALFA results on these objects in the Virgo
region, as well as followup aperture synthesis observations obtained with the
VLA.Comment: To appear in Proceedings of IAU Symp #244, "Dark Galaxies and Lost
Baryons", June 2007, 10 pages including 7 figures and 1 tabl
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Crotalus catalinensis
Number of Pages: 4Integrative BiologyGeological Science
Airborne lidar observations of Arctic polar stratospheric clouds
Polar stratospheric clouds (PSC's) have been detected repeatedly during Arctic and Antarctic winters since 1978/1979 by the SAM II (Stratospheric Aerosol Measurement II) instrument aboard the NIMBUS-7 satellite. PSC's are believed to form when supercooled sulfuric acid droplets freeze, and subsequently grow by deposition of ambient water vapor as the local stratospheric temperature falls below the frost point. In order to study the characteristics of PSC's at higher spatial and temporal resolution than that possible from the satellite observations, aircraft missions were conducted within the Arctic polar night vortex in Jan. 1984 and Jan. 1986 using the NASA Langley Research Center airborne dual polarization ruby lidar system. A synopsis of the 1984 and 1986 PSC observations is presented illustrating short range spatial changes in cloud structure, the variation of backscatter ratio with temperature, and the depolarization characterics of cloud layers. Implications are noted with regard to PSC particle characteristics and the physical process by which the clouds are thougth to form
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Crotalus tortugensis
Number of Pages: 5Integrative BiologyGeological Science
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