ON THE MASS-RADIUS RELATION OF LATE M-DWARFS

We have attempted to rederive an empirical mass-radius relation for main-sequence stars less massive than 0.5Script M sign⊙. Near-infrared photometry (JHK bands) was obtained on about 40 nearby (all with p>0.04″) low-mass stars taken from the Gliese catalogs. From these data and from previously published UBVRI magnitudes, we determine effective temperatures in the standard manner, by fitting blackbody energy distributions to the observed fluxes while allowing for line and band blocking below 1 μm. Together with the known distances, these temperatures and fluxes allow estimates of the radii and luminosities of these stars. Invoking a theoretical mass-luminosity relation, we can then derive the masses of the stars. A comparison of the resultant empirical mass-radius relation with a recent theoretical relation shows that the discrepancy is now∼10%, significantly better than the 20%-25% obtained a decade ago. The improved agreement between theory and observation in this mass regime provides evidence that the mass-losing components in short-period cataclysmic variables are, in general, main-sequence stars.