AAS 199th meeting, Washington, DC, January 2002
Session 18. High Velocity Clouds and The Intergalactic Medium
Display, Monday, January 7, 2002, 9:20am-6:30pm, Exhibit Hall

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[18.01] The Recipe for a High Velocity Cloud

J.R. Masiero, J.C. Charlton, C.W. Churchill (PSU), K.R. Sembach (STScI)

Since their discovery, High Velocity Clouds (HVCs) have been somewhat of an enigma. Historically, HVCs were discovered through their 21 cm emission. However, a number of them can be detected only through absorption. It is obvious that they do not all have exactly the same types of physical structures, but distinctions are not usually made between the different classes of HVCs. Using a combination of archival high resolution STIS (E140M and E230M) and FUSE data, we have analyzed an assortment of HVCs, primarily focusing on the relative ionization of their metals. We present a representative sample of these HVCs which highlight the various classes differing in their phase structure traced by low, moderate, and high ionization chemical transitions (FeII, MgII, SiII, CII, SiIII, SiIV, CIV, and OVI). With photoionization and collisional ionization models, we constrain the densities and sizes of several HVCs.

We acknowledge support through NASA through a Space Telescope Science Institute archival grant.

The author(s) of this abstract have provided an email address for comments about the abstract: masiero@astro.psu.edu

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