Cool Stars 14 - Submitted Abstract # 55
This version created on 05 October 2006

Near-Ultraviolet Spectroscopy of Flares on YZ CMi


Suzanne Hawley, University of Washington
Lucianne Walkowicz, University of Washington
Joel Allred, Drexel University               
Jeff Valenti, Space Telescope Science Institute

Near-ultraviolet spectroscopic data obtained with the HST STIS
instrument on the dMe flare star YZ Canis Minoris (YZ CMi) were
analyzed.  Flare and quiet intervals were identified from the
broadband near-UV light curve, and the spectrum ofeach flare was
separately extracted.  Mg II and Fe II line profiles show similar
behavior during the flares.  Two large flares allowed time-resolved
spectra tobe analyzed, revealing a very broad component to the Mg II k
line profile in atleast one flare spectrum (F9b).  If interpreted as a
velocity, this component requires chromospheric material to be moving
at about 260  km/sec, implying kinetic energy far in excess of the
radiative energy.  The Mg II k flare line profileswere compared to
recent radiative hydrodynamic models of flare atmospheres undergoing
electron beam heating.  The models successfully predict red
enhancements in the line profile with typical velocity of a few
km/sec, but do not reproduce the flares showing blue enhancements, or
the strongly broadened line observed inflare F9b.  A more complete
calculation of redistribution into the line wings, including the
effect of collisions with the electron beam, may resolve the origin of
the excess line broadening.

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