On the ratio of mixing length to scale height in red dwarfs

The discrepancy between the observed and the theoretically predicted luminosity-mass relation in low-mass stars of less than or equal to 0.3 solar mass is examined. The lower observed result is explained by using the latest molecular opacities and by the consequent need to assume a ratio of mixing length to scale height (l/Hp) at T less than 9000 K in the range 0.07 to 0.17, rather than the more conventional values of 1.0 to 2.0. This assumption of a low surface layer l/Hp ratio yields significantly higher central temperatures (and hence luminosities) and quite large radiative cores, regardless of the deeper l/Hp value and equation-of-state uncertainties. The low l/Hp ratio is explained by the interaction of magnetic field with convection. Several consequences of this result, including the interstellar abundance of He-3(+), are discussed.