Other
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...183.1410f&link_type=abstract
American Astronomical Society, 183rd AAS Meeting, #14.10; Bulletin of the American Astronomical Society, Vol. 25, p.1311
Other
Scientific paper
An analysis of high-resolution interstellar absorption line data toward HD 68273 (gamma (2) Vel; O9 I + WC8), obtained with the GHRS on HST, reveals the presence of seven narrow absorption components, with LSR velocities between --23 and +10 km/s. Four of the narrow components arise in H I gas. Accurate depletions are obtained for Fe, Si, and Mg in the strongest of these components, at v(LSR) = 4 km/s, and are suggestive of ``warm'' neutral gas. The observed ratio of Fe and Mg atoms to Si atoms in the dust grains of this component is 2.04+/-0.10, consistent with an olivine grain composition; the Fe/Mg ratio is 1.5+/-0.2. The other three narrow features are identified with H II gas. The electron density in the two strongest H II components, as determined from the Si II* feature, is about 1 cm(-3) . From the S column density in the H II components, we estimate the total pathlength through ionized gas to be 40 pc. With an assumed radius of 60 pc for a wind-blown bubble around gamma (2) Vel, the effective Stromgren radius is thus about 100 pc, requiring that T =~ 50000 K for the WC8 component of the gamma (2) Vel binary. Since the (perhaps) nearby star zeta Puppis is a comparable source of ionizing radiation, this temperature is an upper limit. The GHRS data also show broad absorption components of Si(+3) , C(+3) , and N(+4) which we identify with hot gas. The C(+3) and N(+4) features have widths corresponding to T =~ 4-8 times 10(5) K, consistent with the broad O(+5) line seen in Copernicus data. Despite some observational uncertainties, the ratios of column densities in the broad features agree (to +/-0.1 dex) with theoretical values for warm gas heated by thermal conduction and evaporating into an adjacent hot region. Outward evaporation from an isolated cloud in a hot ambient gas cannot be distinguished, on the basis of these data, from inward evaporation of a warm shell, compressed by an expanding, hot stellar-wind bubble. For halo stars, such as HD 93521, these ratios seem to have quite different values, consistent with cooling of infalling hot gas instead of conductive heating and evaporation.
Fitzpatrick Edward L.
Spitzer Lyman Jr.
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