papers of interest

[Stupendous Man <richmond@stupendous.cis.rit.edu>]

  The latest issue of PASP (Publications of the Astronomical
Society of the Pacific) appeared in my mailbox today.  There are
several papers describing wide-field imaging systems which
may be of interest to TASSians.

   One is "The Pisgah Automated Survey: A Photometric Search 
for Low-mass Detached Eclipsing Binaries and Other Variable Stars",
by Lopez-Morales and Clemens; you can read a preprint at
  
         http://xxx.lanl.gov/abs/astro-ph/0310658

The other is "The Berlin Exoplanet Search Telescope System",
by Rauer et al.  I can't find a copy of this paper in freely
available form, but you can read about it at the project's
WWW site

         http://berlinadmin.dlr.de/Missions/corot/caesp/best.shtml

   The BEST stares for hours at a single field and looks for
the tiny dips caused by transits across a star.  They are using
a Thomson THX7899 CCD chip, which is front-illuminated, to take
images with 5.5-arcsec pixels, covering 3.1 degrees on a side.
With 240-sec exposures, unfiltered, they achieve scatter in
relative photometry of about 0.002-0.003 mag at their bright
end, mag 11, rising to about 0.010 mag at mag 14.  In their
version of the "sigma vs. mag plot", it's interesting to see
the same sort of jump in scatter for the very brightest stars,
where non-linearity occurs; the same feature is visible in
TASS Mark IV measurements.  Remember that it's not fair to
compare this directly to the Mark IV scatter, since the mode
of operation and reduction is very different (and they have
a bigger aperture, and they exposure longer, and have no
filters, etc.)

   The BEST paper notes that, to avoid undersampling the PSF, 
they arrange it so that the stellar PSF "covers at least 2 pixels 
throughout the field".  Hmmm.  What does THAT mean?   Does it
mean that the FWHM is at least 2 pixels, or that 50% of the light
falls on 2 or more pixels, or what?  Moreover, how do they
ensure this?  By de-focussing, or using a heat-gun, or jittering
the mount?  Questions, questions, questions.

                              Michael Richmond