POSTER PAPER 5.14
Structure and Evolution of Low-mass Stars: Where do Magnetic Stars Become Completely Convective?
D. J. Mullan, J. MacDonald
Institute: Bartol Research Institute, University of Delaware
Institute: Department of Physics and Astronomy, University of Delaware
Contact Email: mullan@bartol.udel.edu
Abstract:
Stars on the main sequence
are expected to be completely convective if their mass lies below
a certain value, Mcc.
Standard stellar structure codes
suggest that Mcc is in the range (0.3-0.4) MSun.
However, certain physical effects that are not incorporated in standard
models may alter the value of Mcc significantly.
Here we quantify the alterations that are brought about in
Mcc when we include magnetic field effects. In particular,
we modify the criterion for convective stability in the manner prescribed by
Gough and Tayler (1966).
We find that magnetic M dwarfs tend to have radii that are
larger than expected for their Teff values, or Teff values that
are too low for their radii. Available observational data provide
quantitative support for these structural findings.
Moreover, we find that, given the magnetic fields
which are allowed to exist stably in low-mass stars,
Mcc may fall to values that are as small as 0.1 MSun.
We suggest that this result is pertinent to
understanding why coronae and chromospheres
in active M dwarfs
fail to exhibit detectable alterations at spectral class M3-M4.
Index Keywords: Structure; Magnetic; Completely Convective
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Manuscript submitted: 2001-Aug-31
"The Future of Cool-Star Astrophysics", 2003, Eds. A. Brown,
G. M. Harper, & T. R. Ayres.
Proceedings of 12th Cambridge Workshop on Cool Stars, Stellar Systems,
& The Sun,
© 2003 University of Colorado.