ISOPHOT S Observations of 3 M Dwarfs

Abstract

The M dwarfs GL 832 (spectral type M2), GL 887 (M1), and GL 1 (M2) have been observed with the ISOPHOT spectrophotometers in the range 2.5-12µm at high signal-to-noise ratios. Since optical and ground based near-infrared data are also available, more than 95 % of the total flux is now covered for these objects. It is seen that between 2.5 µm and about 9 µm the fluxes fall off faster than a Rayleigh-Jeans tail of a black body distribution and that for longer wavelengths the decline is smaller. This indicates that the ISO data are probing the region around the temperature minimum and that our stars have some kind of chromosphere although Hα emission is not observed. Comparison with a model indicates that the features are considerably weaker than predicted.