AAS 195th Meeting, January 2000
Session 72. ISM: Neutral Gas
Display, Friday, January 14, 2000, 9:20am-6:30pm, Grand Hall

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[72.07] The Cold, Neutral Gas at d > 200 pc in the Puppis-Vela Region

A. N. Cha (Johns Hopkins U.), M. S. Sahu (NASA/GSFC), H. W. Moos (Johns Hopkins U.), A. Blaauw (Kapteyn Instituut)

We have obtained high resolution (R ~ 80,000), high signal-to-noise (S/N ~ 60-500) Na I \lambda\lambda5889.951, 5895.924Å\ absorption spectra towards approximately 70 early-type stars using the ESO Coudé Auxiliary Telescope (CAT) and the Coudé Echelle Spectrograph (CES). These stars lie in projection in the Puppis-Vela region, from l~~~245\circ to 275\circ and b~~~-15\circ to +5\circ. The distances of the stars in our sample range from ~0.1 to ~1 kpc and galactic altitudes (\midz\mid) range up to ~~160 pc.

We have recently completed a study of the lines of sight to the nearby stars (d~<~200~pc), identifying three distinct velocity components. We have used this foreground gas data to identify LISM absorption features in the complex spectra of more distant (d > 200~pc) sight lines. In addition, accurate distances of the target stars derived from Hipparcos parallax measurements enable upper limits to be placed on the distance of the absorbing material. The approximate location of the gas combined with absorption line trends allows for the identification and systematic analysis of the extended structures that intersect the lines of sight including: (1) the 36\circ-diameter Gum Nebula, an H\alpha emission object extending over most of Puppis-Vela, (2) the IRAS Vela Shell, a ring-like structure discovered from IRAS Super SkyFlux data which has a radius of ~ 8\circ centered at (l,b) = (263\circ,--7\circ), (3) the Vela Molecular Ridge, a complex of giant molecular clouds in the region l = 260\circ to 275\circ and b ± 2\circ, at a distance ~ 1 to 2 kpc, and (4) the Vela Supernova Remnant, a roughly spherical 7.3\circ diameter X-ray bright source centered at (l,b) = (264\circ,--3\circ). In this poster, we present an analysis of the absorption line trends characterizing these large structures in Puppis-Vela.

This work is supported by NASA contract NAS 5-32985 to the Johns Hopkins University and a GTO grant to the STIS IDT.

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