Ambruster and A. Brown (U. CO) obtained a 250 ksec EUVE spectrum of
the least massive star in the EUVE Bright Star List, the single, dM6e
flare star CN Leo. With M = 0.1 M
, CN Leo is both fully
convective and close to the 0.08 M brown dwarf boundary. Part
of the observation was coordinated with an observation of the star by G.
Stringfellow (Penn St.) using the Japanese ASCA X-ray satellite.
Coronal spectroscopy with EUVE is the most efficient way to address
differences in upper atmospheric heating between more massive M dwarfs
with radiative cores (where activity is believed to derive from the
classical 
dynamo), and the fully convective M dwarfs
where the dynamo must operate differently because there no longer is an
interface between the convection zone and the radiative core. Although
fully convective M dwarfs are intrinsically faint at all wavelengths
including X-ray (e.g., log L
= 26.70 for CN Leo), L is
a much higher percentage of L
in these stars than it is for G
and K dwarfs whose L may be considerably greater. Thus changes in
dynamo heating due to the transition to a fully convective structure
should be most visible at coronal temperatures. Reduction of the EUVE
data is currently in progress. The combined EUVE and ASCA spectral data
will then be used to establish the dominant temperature(s) of the outer
atmosphere using Volume Emission Measure modelling. This will allow
comparison of CN Leo's temperature structure and energy balance with
earlier (radiative core) M dwarfs which have been observed with EUVE
(including EV Lac above), in a search for clues to the nature of the
magnetic dynamo in fully convective dwarfs.