Supersonic stellar winds and rapid mass loss in cool stars

Journal Article · Wed Nov 15 04:00:00 EST 1978 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/156595· OSTI ID:6468080

Mullan, D J

Chromospheric pressures have recently been determined among a sample of cool stars by Kelch et al. Combining these with a minimum flux coronal model, we derive a supersonic transition locus (STL) in the H-R diagram. Along the STL, stellar wind flows are expected to become supersonic at the base of the corona: this distinguishes them from transonic winds, where supersonic flow does not set in until some distance away from the star. (The winds discussed here arise from hydrodynamic expansion of hot coronae: radiation pressure plays no role.) We propose that, when a star evolves across the STL, the mass-loss rate will increase discontinuously by a factor of order 50 and expansion will become detectable in the chromosphere. With a plausible factor of order 50 and expansion will become detectable in the chromosphere. With a plausible choice for the pressure difference between the top of the chromosphere and the coronal base, we find that the STL agrees well with the boundary of the domain where giants and supergiants of spectral types G, K, and early M have detectable circumstellar shells (i.e., are undergoing rapid mass loss). In the coronae of these stars, we argue that supersonic wind flow is not seriously impeded by magnetic structures (if such exist).Rates of mass loss by means of supersonic winds are estimated to be 1.6 x 10/sup -9/ R/sup 1/2/M solar masses per year (where R and M are the stellar radius and mass in solar units). The mass-loss rates predicted here are such that a 5 M/sub s/ star will lose approximately 0.4 M/sub s/ star will lose approximately 0.4 M/sub s/ during the first phase of core helium burning. Following helium exhaustion in the core, the mass-loss rate predicted here is too slow to prevent stars of mass 3--9 M/sub s/ from becoming carbon-detonation supernovae. Population II stars of mass 0.7--0.9 M/sub s/ are predicted to lose 0.2--0.3 M/sub s/ prior to the helium flash.

• Research Organization: Bartol Research Foundation of the Franklin Institute, Universitt of Delaware
• OSTI ID: 6468080
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 226:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
DIAGRAMS
FLUID FLOW
GIANT STARS
HERTZSPRUNG-RUSSELL DIAGRAM
MATHEMATICAL MODELS
NUCLEOSYNTHESIS
STAR EVOLUTION
STAR MODELS
STARS
STELLAR ATMOSPHERES
STELLAR WINDS
SUPERGIANT STARS
SUPERSONIC FLOW
TRANSONIC FLOW