  Accurately measuring the magnetic field in the ISM is essential for
understanding star-formation processes. We searched archival data of the
Submillimeter Array (SMA) for evidence of circular polarization in common
molecular tracers, most notably CO. This circular polarization possibly arises
from anisotropic resonant scattering, which would imply that some background
linearly polarized radiation is being converted to circular polarization. We
find circular polarization in the star-forming regions NGC7538 (in CO) and
Orion KL (in CO and SiO), as well as in the carbon star IRC+10216 (in CS, SiS,
H$^{13}$CN and CO) at high enough levels to suggest that the presence of
circular polarization in these spectral lines is common for such objects. This
implies that measuring circular polarization is important when studying
magnetic fields through the linear polarization of molecular spectral lines in
the interstellar medium. We also provide a simple Python wrapper for the Miriad
data reduction package.
