CHROMOSPHERIC DIAGNOSTICS IN LATE-TYPE STARS

We present moderate (1.4 angstrom) and low (6 angstrom) resolution spectroscopic observations of late type dwarfs covering a broad range of activity. The strength of the TiO band in 4762 angstrom is used for spectral classification. Calibrated fluxes for the Balmer and the Ca II H and K lines are derived. H-alpha equivalent widths are given for those stars where the line is in absorption as well as those in emission. We confirm that stars with no detectable or very weak H-alpha do exist. We also show that stars with very weak or no detectable emission in Ca II H and K also exist, this occurring preferentially in late M dwarfs. Although this can be explained in terms of reduced non-radiative heating in the chromosphere, our results can not be conclusive due to the limited resolution of the data.