High Contrast Infrared Imaging and Polarimetry of Dusty Disks around
Herbig Ae/Be Stars
Circumstellar disks are now known to be very common around young
stars, but actually imaging these disks remains a formidable
challenge. Both high angular resolution and high contrast are
required in order to separate faint dust-scattered light from the
background of much brighter starlight. Adaptive optics is
increasingly capable of delivering the necessary performance for
spatially resolved imaging of disks from the ground. One powerful
technique is differential imaging polarimetry, which can reject
unpolarized starlight and thus reveal faint polarized light scattered
from circumstellar dust. An alternate approach is to change the rules
of the game, for instance by moving to a different wavelength at
which the star is fainter and the dust is brighter, such as the
mid-infrared.
In fact these two approaches are complimentary, with near-IR
polarimetry tracing dust in scattered light while mid-IR imaging
traces thermal and PAH emission. I have employed these techniques to
survey 110 Herbig Ae/Be stars (pre-main-sequence stars of
intermediate mass), resolving extended circumstellar dust around 44
of them. The observed dust geometries are highly varied, ranging from
circumstellar disks to bipolar envelopes to complex asymmetric
nebulae. In this talk I will briefly describe the AO differential
polarimeter I developed at Lick Observatory, summarize the overall
results of my near-IR and mid-IR survey of Herbig stars, and discuss
in depth a few of the most interesting (and most puzzling!) of the
observed sources.