  The polarization of light across spectral lines contains information about
the circumstellar material on small spatial scales. Many models relate the
circumstellar environment to observable polarization changes across spectral
lines. However, measuring signals at the 0.1% level requires a very careful
control of systematic effects.
  We have recently built a high-resolution spectropolarimeter for the HiVIS
spectrograph on the 3.67m AEOS telescope and have obtained a large number of
high precision spectropolarimetric observations of Herbig Ae/Be, Classical Be
and other stars. The detected linear polarization varies from our typical
detection threshold near 0.1% up to 2%. This polarization effect is generally
not coincident with the H-alpha emission peak but is detected only in the
absorptive part of the line profile and varies with the absorption. These
detections are largely inconsistent with the traditional scattering models and
inspired a new explanation of their polarization.
  We developed a new spectropolarimetric model and argue that polarization in
absorption is evidence of optical pumping. We argue that, while scattering
theory fits many Be and emission-line star observations, this new theory has
much more potential to explain polarization-in-absorption as seen in Herbig
Ae/Be and other stellar systems.
  This thesis presents a large spectropolarimetric study that combines new
instrumentation, custom processing software, thorough calibrations,
cross-instrument comparisons, a massive observing campaign on many targets,
comparison of current theories on multiple objects and finally the creation of
a new theory.
