AAS 197, January 2001
Session 7. Gas in the Galactic ISM
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

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[7.21] FUSE Observations of Interstellar Absorption in the Galactic Halo: the Sight Line to von Zeippel 1128

J.C. Howk, K.R. Sembach (JHU), B.D. Savage (Wisc.), FUSE Science Team

We present high signal-to-noise Far Ultraviolet Spectroscopic Explorer (FUSE) observations of interstellar absorption toward the faint post-AGB star von Zeippel 1128 [V=14.9; (l,b) = (42.5, +78.7)] in the globular cluster M 3. The FUSE data cover the 905-1187 Ang wavelength region with a spectral resolution of 20 km/s. von Zeippel 1128 lies 9.5 kpc above the Galactic disk; thus, our measurements of interstellar absorption along this sight line probe the entire Galactic halo.

These data provide a fundamentally new means for studying the kinematics of the warm ionized medium (WIM), its ionization and relationship to other (colder, hotter) gases within the ISM. We detect the WIM through absorption lines of S III, Fe III, N II, N III, and C III, which are centered at -35 km/s (LSR). We detect hot, collisionally-ionized gas through strong O VI absorption with a column density of log N(O VI) = 14.44+/-0.02. The O VI profile is very well fit by a single broad Gaussian centered at -20 km/sec (LSR) with FWHM=75 km/sec, implying a temperature below 2x10(6) K. If the temperature of the material is 3x10(5) K, where the abundance of O VI peaks in collisional ionization equilibrium, then non-thermal motions with a Gaussian velocity distribution account for most (roughly 70 km/sec) of this breadth. Warm neutral gas is also detected in species such as O I, C II, Si II, and Fe II.

We comment on the kinematics of the warm and hot gas along this sightline, which probe the bulk vertical motions and turbulence of interstellar matter in the Galactic halo. We also discuss the possibility of using the high-order H I Lyman series lines in our dataset to search for diffuse interstellar material associated with the globular cluster M 3.

This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. Financial support has been provided by NASA contract NAS5-32985.

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