Optical Spectroscopy of Sightlines Toward High Velocity Clouds

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Session 61 -- Molecular Clouds, Star Formation
Display presentation, Thursday, 9:20-4:00, Pauley Room

[61.01] Optical Spectroscopy of Sightlines Toward High Velocity Clouds

Bryan E. Penprase (IPAC/Caltech), Barry Welsh (NASA Headquarters), Chris Blades (STScI), Elise Albert (US Naval Academy), Tony Danks (GSFC)

We report spectroscopic observations of 15 sightlines toward high velocity clouds observed first by Bajaja, et al (1989). 15 supergiant stars were selected which appear toward the highest intensity H I contours, and each star was observed at high resolution in the lines of Ca II K and Na I D, with a resolving power $\lambda/\delta\lambda$ $\ge$ 70,000. The observed component strengths are analyzed to determine variations in R(CaII,NaI) in sightlines which cross the inner 3 kpc region of the galaxy, and we report the existence of several components which have observed CaII velocities of v(CaII) $>$ 80 km s$^{-1}$.

The absorption lines are used to place constraints on the distances to the high velocity cloud complexes, and the observed line profile structure is used to infer the dynamics and ionization state of the material along the sightlines. For some of the more distant sightlines, which have r $>$ 5 kpc, we present low-resolution classification spectroscopic observations, which are used to derive improved spectral types and stellar distance estimates. Some of the sightlines were also observed to have lower column densities of Ca II than expected, and possible explainations for the observed values of N(Ca II) are examined. The spectroscopic observations are used to improve our understanding of the distance and ionization states of absorbing clouds in the galactic plane, and provide important diagnostics of the physical conditions in distant sightlines of the galactic plane.


Bajaja, E., Cappa de Nicolau, C.E., Martin, M.C., Morras, R., Olano, C.A., and Poppel, W.G.L. 1989, Astron. Astrophys. Suppl., 78, 345.

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