Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979apj...231..128b&link_type=abstract
Astrophysical Journal, Part 1, vol. 231, July 1, 1979, p. 128-138.
Astronomy and Astrophysics
Astrophysics
34
M Stars, Red Giant Stars, Stellar Envelopes, Early Stars, Late Stars, Radiation Pressure, Spectrograms
Scientific paper
The average circumstellar envelopes of 61 red giants of spectral types M0 through M7 are studied, and information is deduced concerning the velocity structure in the envelopes as well as the mass-loss mechanism. Positions of red and blue edges of the circumstellar Ca II K4 profile are used to derive information on shell turbulent velocities and velocity gradients within the envelopes. The results obtained indicate that: (1) acceleration to a terminal velocity occurs extremely rapidly or the mass-loss mechanism acts upon Ca III, which recombines only after the terminal velocity has been reached; (2) the turbulence must be less than 2 km/s in the shells of the M0 giants and should increase to a value of at least 4 km/s for the M6 giants; (3) the observed broadening of the K4 profile toward later spectral types must be due at least in part to the increase in turbulence toward the later types; (4) shell expansion begins well within the stellar chromospheres; and (5) the mass-loss mechanism might involve supersonic winds rather than radiation pressure on grains.
Boesgaard Ann Merchant
Hagen Wim
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