An Optical Survey of Large Interstellar Structures

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Session 36 -- ISM: Structure, Molecular Clouds
Display presentation, Wednesday, June 14, 1995, 9:20am - 6:30pm

[36.11] An Optical Survey of Large Interstellar Structures

Y.P. Lee, L. Danly (ST ScI), C. Sneden, D. Hiltgen (U. Texas -- Austin), C.E. Albert (US Naval Academy), J. Krick (Baltimore City College H.S.), H. Baldwin, E. Jackson (Friends H.S. of Baltimore)

Over the past decade, studies of the interstellar medium in our galaxy have highlighted the prevalence and importance of large-scale structures in the distribution of gas in the disk and halo. Heiles (1984) presented a catalog of H I Shells, Shell-like loops and Worms. Some of these structures are believed to be several kiloparsecs in size and show coherent structure in space and velocity. To study the distances, kinematics and abundances of these H I structures in the galactic halo, we obtained interstellar absorption spectra of Ca II H and K lines and Na I D1, D2 lines at high resolution ($~7$ km/s) toward stars in the directions of 6 Heiles HI loops. Here we present the initial results of our observations. We observed 62 stars at a variety of distances in the direction of each loop. Interstellar absoprtion lines of gas moving at $~ -50$ km/s were detected along a number of sightlines and the distances to these gaseous structures were estimated base on the stellar distances. Several lines of sight have been identified for follow-up study at 21 cm and ultraviolet wavelengths.

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