Structure of the winds and coronae of O stars derived from H. cap alpha. line-profile analyses
Several recent studies of the emission-line spectra of hot stars have led to the conclusion that there are high-temperature regions or coronae in the stellar winds. To test this idea, the effects of coronal regions on H..cap alpha.. line profiles are studied by using the Sobolev escape-probability method. The temperature is assumed to rise rapidly at the base to coronal values and then, after a small radial distance, to decrease owing to radiative recombination. Such a structure gives rise to P Cygni lines that have flat emission components. The spatial extent of the coronal region and velocity structure of the flow above the coronal region can be probed with the H..cap alpha.. profile. The analysis is applied to zeta Ori, 09.7 Ib, and it is found that the corona must have a small thickness, less than 10% of the stellar radius. The velocity structure of the wind is deduced from a fit of the theoretical to the observed line profile. The velocity does not increase steadily outward, but reaches a plateau and then at about 2.5 R/sub asterisk/ experiences a second rapid acceleration to terminal speeds. If the temperature above the coronal regions has cool values (2--3 x 10/sup 4/ K) appropriate for a gas in radiative equilibrium, we get good agreement with mass-loss rates derived for O stars from ultraviolet line profile and IR excess analyses. If the temperature in the wind is of order 2 x 10/sup 5/ K, mass-loss rates larger than the single-scattering theoretical limit of L/v/sub infinity/c are required. It is argued that hard radiation from a small coronal zone can produce the high stages of ionization such as O VI observed in the winds of hot stars.. Thus a model which is consistent with the H..cap alpha.., IR, and UV data of hot stars has a very small coronal zone surrounded by a cool stellar wind.
- Research Organization:
- University of Wisconsin--Madison
- OSTI ID:
- 5041807
- Journal Information:
- Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 220:2; ISSN ASJOA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
BALMER LINES
ELECTROMAGNETIC RADIATION
EMISSION SPECTRA
GIANT STARS
INFRARED RADIATION
MAIN SEQUENCE STARS
MATHEMATICAL MODELS
RADIATIONS
SPECTRA
STAR MODELS
STARS
STELLAR ATMOSPHERES
STELLAR WINDS
SUPERGIANT STARS
VELOCITY