Are Magnetically Active Low‐Mass M Dwarfs Completely Convective?

Stars on the main sequence are expected to be completely convective if their mass lies below a certain value, M cc . Standard stellar structure codes suggest that M cc is in the range 0.3-0.4 M ☉ . In the present paper we examine several nonstandard additions to stellar structure in order to quantify their effects on the value of M cc . We find that by including magnetic field effects, M cc may fall to values that are significantly smaller than the standard range. This result is of interest in understanding why coronae and chromospheres in active M dwarfs fail to exhibit detectable alterations at spectral class M3-M4. The structural properties of our magnetic models also explain why active M dwarfs tend to have radii that are larger than expected for their T eff values or T eff values that are too low for their radii. Our results lead us to predict that certain stars that are classified as late L or T stars may actually have masses of 0.1-0.15 M ☉ .