Circumstellar envelopes of hot stars provide tantalizing clues about
the underlying physics of the system. Unfortunately they also provide
great challenges to the observer - namely, for most stars the circumstellar
envelopes are too small to be resolved with current techniques. For
this reason, we must employ more indirect methods, such as polarimetry,
to investigate the geometry and physical characteristics of the envelope.
The observed polarization is produced by scattering of starlight within
the envelope. At the same time, the envelope attenuates the polarized
flux, imprinting the envelope opacity signature on the polarization spectrum.
From this we can estimate the temperature and density of the envelope itself.
Combining polarization measurements with other techniques, particularly
interferometry, we can learn more about the geometry of the envelope.
Initial efforts in these areas provide glimpses of circumstellar disks
and even hints of time-variable asymmetries within these disks. New instruments
on the horizon, such as the CHARA array, promise great breakthroughs in
these areas, due to their higher sensitivity and improved resolution.