We present commissioning data for the POLISH instrument obtained on the Hale
5-m telescope. The goal of this high precision polarimeter is to constrain
orbital inclination of high mass X-ray binaries and to therefore obtain
independent mass estimates for their black hole companions. We have obtained
photon shot noise limited precision on standard stars, and we have measured the
polarization of bright stars at the part per million level on a nightly basis.
Systematic effects have been reduced to less than 1% of the measured
polarization for polarized sources and to the part per million level for weakly
polarized sources. The high sensitivity of this instrument to asymmetry
suggests that valuable contributions will be made in many other fields,
including studies of extrasolar planets, debris disks, and stellar
astrophysics.Comment: 35 pages, 10 figures, accepted for publication in PAS
