Chromospheric models of dwarf M stars.

MAUAS, P J D; FALCHI, A.; PASQUINI, L.; PALLAVICINI, R.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 1997 vol. 326 p. 249 - 256

0004-6361

We present chromospheric models for two dM stars considered as ``basal´´ stars due to the low level of chromospheric activity, and compare them with the model for a very active, flare star obtained in a previous paper. These models are not based on a single spectral feature, but on the continuum in a broad wavelength range (3500-9000Å), 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 the active stars have both a chromospheric temperature rise at larger column mass and a higher chromospheric temperature. These characteristics are responsible for the presence of the Balmer lines in emission in the dMe stars. We also show that the additional energy required to transform a dM star into an active star must be deposited in the high chromosphere, just below the transition region.