AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 71. Between the Stars II: The ISM, Galactic and Extragalactic
Display, Wednesday, June 2, 1999, 10:00am-6:30pm, Southwest Exhibit Hall

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[71.19] The Cold, Neutral Gas in the Puppis-Vela Region

A. N. Cha (JHU), M. S. Sahu (NASA/GSFC), H. W. Moos (JHU), A. Blaauw (Kapteyn Astronomical Institute)

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 Coud\acute{e} Auxillary Telescope (CAT) and the Coud\acute{e} 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.

The 36\circ-diameter Gum Nebula, the H\alpha emission object with the largest known angular dimensions in the sky, extends over most of Puppis-Vela. In addition to the Gum Nebula, three other extended structures lie (in projection) in this region: (1) the IRAS Vela Shell, a ring-like structure discovered from IRAS Super SkyFlux data which has a radius of ~ 8\circ centred at (l,b) = (263\circ,--7\circ), (2) 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 (3) the Vela Supernova Remnant, a roughly spherical 7.3\circ diameter X-ray bright source centered at (l,b) = (264\circ,--3\circ).

The sight lines to the nearby stars (< 200 pc) in our sample, allow us to study the distribution and kinematics of Local ISM (LISM) gas in the Puppis-Vela region of the Milky Way, while the sight lines to the more distant stars penetrate one or more of the aformentioned interstellar structures. The neutral gas velocities observed in the LISM range between vLSR = -1 and +10 km s-1, and the associated Local Interstellar Cloud (LIC) and Local Bubble components (if present) are identified. The stars inside the IRAS Vela Shell, within a distance of 450 pc, show systematic velocities of vLSR = -22 to -1 km s-1 (excluding LISM gas), while those beyond 450 pc each exhibit an additional component between +12 km s-1 < vLSR < +22 km s-1, revealing the front and rear expanding edges of the shell, respectively. The sight lines intersecting multiple objects in the vicinity, however, feature spectra that appear more complex and varied. In this poster, we present a systematic analysis of absorption line trends associated with the LISM and extended structures in the Puppis-Vela region.

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