CHROMOSPHERIC MODELS OF DWARF M-STAR

We present chromospheric models for two dM stars considered as ''basal '' stars due to the low level of chromospheric activity, and compare t hem with the model for a very active, flare star obtained in a previou s paper. These models are not based on a single spectral feature, but on the continuum in a broad wavelength range (3500-9000 Angstrom), on many line profiles corresponding to three different atoms (H, Ca, Na), and on the Mg II h and k flux. We show that a marked chromosphere is present even for stars with the lowest levels of activity, and that th e active stars have both a chromospheric temperature rise at larger co lumn mass and a higher chromospheric temperature. These characteristic s are responsible for the presence of the Balmer lines in emission in the dMe stars. We also show that the additional energy required to tra nsform a dM star into an active star must be deposited in the high chr omosphere, just below the transition region.