Title:  Coronal Activity in Rapidly Rotating Stars

Object:    HD 79826
Exposure:  50 ks
Lead scientist: David Huenemoerder
[X] Primary or [ ] Backup
Constraints (none/easy/average) NONE
[ ] TOO?

Brief description:

  Using photometry obtained with the Chandra guide star system, we
  have identified HD 79826 (G5) as a very short period (0.5 d) active
  binary of the RS CVn type. As such, it is important for probing
  stellar activity at the extreme limits of magnetic dynamo generation
  where X-ray luminosity saturation occurs.  We will study the
  variability of line and continuum emission sampled over the
  rotational period in order to probe the geometric distribution and
  volume of emitting plasma, and relate to hypotheses for
  supersaturation which dictate different behaviors for strength and
  modulation.  This newly discovered very short period eclipsing
  binary is an important case for comparison with other short period
  active systems like AB Dor, 44 Boo, and VW Cep, in the regime of
  extreme magnetic dynamos.  

  The ROSAT all-sky survey count rate is 0.55 counts/s.  We estimate
  that its HETGS count rate would be about 0.14 counts/s.  A 50ks
  exposure will provide a good exposure of the coronal emission lines
  and provide some sampling of variability around a full orbit. (A
  comparable case is 24 UMa, obsid 3471, 44ks, 0.16 counts/s
  MEG-band; <http://tgcat.mit.edu/tgPlot.php?t=P&i=1708>).

  References:

   chandra variable guide star catalog:
     <http://cxc.harvard.edu/vguide/details.php?agascid=716452328&Q=351_ded17e449950b431>

   period, spectral types, light curve:
        parihar et al, 2009 (MNRAS 593, 607)