We propose to do spectrophotometry using ISOPHOT covering the 2-
 12 micron range of a selection of M dwarfs, which are also GTO
 program targets for photometric observations extending to much
 longer wavelengths.  The goal is to determine the temperature
 stratification, effective temperature, bolometric luminosity and
 the general atmospheric structure of low mass stars using a more
 sensitive and accurate approach than studies at shorter
 wavelengths.  We hope also to study how the atmospheric structure
 depends both on effective temperature (mass) and on the degree of
 chromospheric/coronal activity.

 The temperature stratification especially high in M dwarf
 atmospheres is complicated and uncertain mainly because there is
 probably only a very thin outer radiative zone, which sets the
 boundary for the adiabatic convection zone extending to the center
 of the star.  The effective temperature of the star is also
 sensitive to this boundary.  Our main purpose is to determine the
 depth of the radiative layer, and how this depends on stellar
 parameters and surface activity.

 In the ISO spectral region, the continuum is generally formed high
 in the physical atmosphere and is therefore sampling the critical
 temperature range.    The main reason for this is the dominance of
 the H-minus free-free opacity; it increases by nearly two orders
 of magnitude over the 2-12 micron range.  Optical and near-IR
 wavelength studies, on the other hand, are complicated by the
 dominance of much more uncertain and complex molecular and atomic
 bands.