Small-Scale Structure of O VI Interstellar Gas in the Direction of the Globular Cluster NGC 6752
Abstract
In order to study the small-scale structure of hot interstellar gas, we obtained Far Ultraviolet Spectroscopic Explorer interstellar O VI absorption spectra of four post-extreme horizontal branch stars in the globular cluster NGC 6752 ([l,b]=[336.50d,-25.63d], d=3.9 kpc, z=-1.7 kpc). The good-quality spectra of these stars allow us to measure both lines of the O VI doublet at 1031.926 and 1037.617 Å. The close proximity of these stars permits us to probe the hot interstellar gas over angular scales of only 2.2m-8.9m, corresponding to spatial scales of <~2.5-10.1 pc. On these scales we detect no variations in the O VI column density and velocity distribution. The average column density is log<N(O VI)>=14.34+/-0.02 (log<N⊥(O VI)>=13.98). The measured velocity dispersions of the O VI absorption are also indistinguishable. Including the earlier results of Howk et al., this study suggests that interstellar O VI is smooth on scales Δθ<~12', corresponding to a spatial scale of <~10 pc, and is quite patchy at larger scales. Although such small scales are only probed in a few directions, this suggests a characteristic size scale for the regions producing collisionally ionized O VI in the Galaxy.
Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by the Johns Hopkins University under NASA contract NAS 5-32985.- Publication:
-
Publications of the Astronomical Society of the Pacific
- Pub Date:
- October 2004
- DOI:
- 10.1086/425107
- arXiv:
- arXiv:astro-ph/0408309
- Bibcode:
- 2004PASP..116..895L
- Keywords:
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- ISM: Clouds;
- ISM: Structure;
- ultraviolet: ISM;
- Astrophysics
- E-Print:
- Accepted for publication in the PASP (to appear in the October 2004 issue)