Astronomy and Astrophysics – Astronomy
Scientific paper
May 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...194.1309b&link_type=abstract
American Astronomical Society, 194th AAS Meeting, #13.09; Bulletin of the American Astronomical Society, Vol. 31, p.846
Astronomy and Astrophysics
Astronomy
Scientific paper
Ultraviolet resonance line profiles of rapidly-rotating near main-sequence B stars indicate that the two-dimensional ionization structure of the circumstellar envelope can be crucial to our understanding of the mass-loss rate. We investigate these two-dimensional effects through the use of a radiation transfer model to construct piece-wise spherical ionization fractions for the wind-compressed disk model of a rotating stellar wind. Using these ionization fractions, we generate theoretical line profiles using a two-dimensional Monte Carlo simulation of the radiation transport for the UV resonance lines of Si iii, Si iv, C iii, C iv, and N v. For the B2.5 IV star chosen for this study, we find the mass-loss rate to be on the order of a few times 10(-9) Msuntextrm { yr}(-1) and the X-ray emission measure log EM_X ~ 52.5 cm(-3) . This result is consistent with observed X-ray luminosities as well as UV resonance line profiles. Our mass-loss rate is higher by a factor of 5--10 over those predicted theoretically (via spherically symmetric radiation-driven wind theory) and observationally (due to uncertainties in the ionization fractions). In addition, we also examine the effects of a latitudinal density gradient on the line profiles. We find that the line profiles are sensitive to two-dimensional effects, showing disproportionate amounts of emission versus absorption as the viewing location changes from pole to equator. Specifically, N v, which is abundant in the polar regions and depleted in the equator, shows enhanced emission for an observer looking edge-on to the equatorial wind-compressed disk. We show that spherically symmetric models cannot account for the anomalously strong emission or absorption resulting from a latitudinal ionization gradient in the wind. This work has been supported under NASA grants NAG5-3447 (BPA) and NAG5-3248 (JEB) to the University of Toledo.
Abbott B. P.
Bjorkman Jon E.
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