The relation between microturbulence and mass loss from supergiants

Details The relation between microturbulence and mass loss from supergiants The relation between microturbulence and mass loss from supergiants

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...291..856l&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 291, no. 3, p. 856-868

Astronomy and Astrophysics

Astrophysics

19

Atmospheric Models, Line Spectra, Photosphere, Stellar Winds, Supergiant Stars, Turbulence, Flux Density, Ionization, Spectral Line Width, Stellar Models, Temperature Gradients, Velocity Distribution

Scientific paper

We investigate the effect of stellar mass loss on the photospheric lines of supergiants of spectral types O to late F. High mass loss produces a velocity gradient in the photospheres of supergiants which affects the profiles, the equivalent widths and the radial velocities of the lines. We show that the use of hydrostatic model atmospheres for the study of the equivalent widths of photospheric lines in the spectra of supergiants will result in large apparent microturbulent velocities. The derived microturbulent velocities do not reflect the presence of real microturbulence (i.e. small-scale isotropic motions with a Gaussian velocity distribution), but they reflect the presence of the velocity gradient in the photospheric layers. Therefore the apparent microturbulent velocity can be used to estimate the mass loss rates from supergiants. This explains the empirical relation between the mass loss rate of supergiants and the microturbulent velocity, or the inferred microturbulent pressure, found by Nieuwenhuijzen et al. (1992, 1994). We conclude that the mass loss from A, F and possible early-G supergiants is not due to the pressure of the photospheric microturbulence, but that the apparent photospheric microturbulence is due to mass loss.

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