Statistics – Computation
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...412..312m&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 412, no. 1, p. 312-323.
Statistics
Computation
23
Acoustics, Dwarf Stars, Lyman Alpha Radiation, M Stars, Magnesium, Stellar Models, Chromosphere, Computational Astrophysics, Hydrodynamic Equations, Photosphere, Radiative Transfer, Shock Heating, Stellar Atmospheres
Scientific paper
Surface fluxes of Mg II and Ly-alpha from a sample of M dwarfs have been reported by Panagi and Mathioudakis (PM, 1992). In order to determine if acoustic effects can reproduce the fluxes in the least active ('basal') stars in the PM sample, we have constructed steady state models of plane-parallel atmospheres with T(eff) = 3000 and 4000 K including heating by shock dissipation. The models incorporate radiative losses in the chromosphere by solving the transfer equation for two strong lines (Mg II k and Ly-alpha). Predictions of standard weak shock theory are expected to overestimate the rate of energy deposition in the chromospheres of M dwarfs compared to the rate of deposition in F, G, or K dwarfs. In order to incorporate this effect in M dwarfs, we compute a series of atmospheric models in which, for a given T(eff), the standard weak shock dissipation rate is reduced by a series of factors F(r). Although the input acoustic flux F(mech) may in principle be determined uniquely by T(eff) and log g, the correct value to use in any particular case is not well known. We therefore use F(mech) and F(r) as parameters to construct a family of M dwarf models at various T(eff) and g. Comparing with the observed fluxes in the least active M dwarfs of the PM sample, we find that our models reproduce the observed fluxes of both Mg II and Ly-alpha best if F(mech) is close to the value predicted by Bohn (1984) and if F(r) is approximately equal to 10-20.
Cheng Qing-Qi
Mullan Dermott J.
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