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Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Early type high-velocity stars in the solar neighborhood. IV - Four-color and H-beta photometry
Results are presented from photometric obaservations in the Stromgrenuvby four-color and H-beta systems of early-type high-velocity stars inthe solar neighborhood. Several types of photometrically peculiar starsare selected on the basis of their Stromgren indices and areprovisionally identified as peculiar A stars, field horizontal-branchstars, metal-poor stars near the Population II and old-disk turnoffs,metal-poor blue stragglers, or metallic-line A stars. Numerousphotometrically normal stars were also found.
| Interstellar reddening in the Southern Hemisphere. I - The UVBY beta observations
The uvby-beta photometric data obtained from a Southern Hemisphereobservational project is presented. A uvby-beta photometric network ofnearly 3900 A and early F stars has been established with the intentthat the stars serve as 'space probes' for measurements of interstellarreddening.
| The origin of the GUM nebula
Obsrvations and theoretical investigations of the Gum nebula (GN) sinceabout 1971 are reviewed. Direct observations of the GN, the Vela Xsupernova remnant (SNR), the Vela pulsar, and other stars in or near theGN are discussed with those of related phenomena such as the radio loopsand known SNRs; the emphasis is on studies of the interstellarabsorption lines, the evidence for hot gas in the GN, and the extendeddiffuse emission. The four basic models proposed for the GN areconsidered: a fossil Stromgren sphere, an old SNR, an H II region, or asuperbubble. The GN physical parameters predicted by each model arelisted in a table and compared. A minimum explanation which attributesthe 36 x 36-deg filamentary structure and the 125-pc radius structure tothe action of the stellar winds from Zeta Pup and Gamma-2 Vel (andperhaps the effect of a Vel X supernova explosion 20,000 years ago) isfound most appropriate, at least until the questions of the netexpansion rate of the GN (about 20 km/sec or about zero?) and theexistence of the diffuse emission beyond the filamentary structure areresolved by observations.
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