LSST's DC Bias Against Planets and Galactic-Plane Science
  An LSST-like survey of the Galactic plane (deep images every 3-4 days) could
probe the Galactic distribution of planets by two distinct methods:
gravitational microlensing of planets beyond the snow line and transits by
planets very close to their hosts. The survey would identify over 250
disk-lens/disk-source microlensing events per year that peak at r<19, including
10% reaching the high magnification A>100 that makes them especially sensitive
to planets. Intensive followup of these events would be required to find
planets, similar to what is done presently for Galactic bulge microlensing. The
same data would enable a wealth of other science, including detection of
isolated black holes, systematic study of brown-dwarf binaries, a pre-explosion
lightcurve of the next Galactic supernova, pre-explosion lightcurves of stellar
mergers, early nova lightcurves, proper motions of many more stars than can be
reached by GAIA, and probably much more. As usual, the most exciting
discoveries from probing the huge parameter space encompassed by Galactic-plane
stellar populations might well be serendipitous. Unfortunately, the LSST
collaboration plans to exclude the first and fourth quadrants of the Galactic
plane from their "synoptic" observations because the DC image that resulted
from repeated observations would be limited by crowding. I demonstrate that the
majority of this science can be recovered by employing well-developed image
subtraction analysis methods, and that the cost to other (high Galactic
latitude) science would be negligible.
