The theoretical massmagnitude relation of low mass stars and its metallicity dependence
Abstract
We investigate the dependence of theoretically generated massabsolute magnitude relations on stellar models. Using uptodate physics we compute models of stars in the mass range 0.1 < m < 1 M_odot. We compare the solarmetallicity models with our older models and also with recent models computed by others. We further compare them with an empirical massabsolute magnitude relation that best fits the observed data. At a given mass below 0.6 M_odot the effective temperatures differ substantially from model to model. However, taken individually, each set of models is in good agreement with observations in the massluminosity plane. A minimum in the derivative dm/dM_V at M_V ~ 11.5, which is due to H_2 formation and the establishment of a fully convective stellar interior, is present in all photometric bands, for all models, but its position changes from model to model. This minimum leads to a maximum in the stellar luminosity function for Galactic disc stars at M_V ~ 11.5, M_bol ~ 9.8. Precise stellar models should locate this maximum in the stellar luminosity function at the same magnitude as observations. This is an extra constraint on lowmass stellar models. Models which incorporate the most realistic theoretical atmospheres and the most recent equation of state and opacities can satisfy this constraint. These models are also in best agreement with the most recent luminosityeffective temperature and massluminosity data. Each set of our models of a given metallicity (in the range 0.2 > [Fe/H] > 2.3) shows a maximum in dm/dM_bol, which moves to brighter bolometric magnitudes with decreasing metallicity. The change in location of the maximum, as a function of [Fe/H], follows the location of structure in luminosity functions for stellar populations with different metal abundances. This structure, seen in all observed stellar populations, can be accounted for by the massluminosity relation and does not require a maximum in the stellar mass function at m ~ 0.3 M_odot.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 May 1997
 DOI:
 10.1093/mnras/287.2.402
 arXiv:
 arXiv:astroph/9701213
 Bibcode:
 1997MNRAS.287..402K
 Keywords:

 Astrophysics
 EPrint:
 MNRAS (in press), 15 pages, 1 appendix, plain TeX, 9 postscript figures