Possible M dwarf enrichment in the semistellar nucleus of M31

The paper presents new observations of the equivalent width of the Na I 8190 absorption feature in M31 and M32. The strength of Na I 8190 is a sensitive indicator of the relative numbers of cool M dwarfs and M giants in an old stellar population. The line is significantly stronger in the semistellar nucleus of M31 than in the surrounding bulge or in the nucleus of M32. A variety of arguments suggest that this line enhancement is not due to metallicity differences alone. The observations thus apparently reopen the possibility suggested by Spinrad and Taylor that the nucleus of M31 is measurably richer in M dwarfs than either the surrounding bulge or M32. A number of observations in other spectral features are suggested which might test this possibility. If the nucleus actually is dwarf-enriched, the predicted increase in mass-to-light ratio would agree reasonably well with dynamical estimates of M/L, which also indicate a higher mass-to-light ratio in the semistellar nucleus.