A high angular resolution survey of circumstellar dust around Herbig Ae/Be stars

This thesis presents the development of a sensitive near-infrared differential imaging polarimeter, and its subsequent use, combined with mid infrared imaging, to survey circumstellar dust around 110 Herbig Ae/Be stars.; Planets are born in dusty circumstellar disks around young stars. By imaging such disks we can learn about the environment and physical processes that assemble planets from primordial dust and gas. But these observations are challenging on account of the high angular resolution and high dynamic range necessary to detect the disk's faint reflected light against a far brighter background of stellar light.; One powerful method for obtaining the necessary contrast is the use of differential polarimetry to separate polarized dust-scattered light from unpolarized starlight. For this reason, I have developed a differential polarimetry mode for IRCAL, the adaptive optics science camera at Lick Observatory, which uses a YLF Wollaston prism beamsplitter to attenuate 98-99% of stellar light. I describe this instrument, summarize the data reduction and image analysis algorithms employed, and discuss lessons learned for future high-contrast imaging systems. A second strategy for high contrast science is to obtain observations at mid-infrared wavelengths, where dust is bright and stellar light is comparatively faint. These two techniques are complementary, respectively probing scattered and thermal light, and their multiwavelength combination can help constrain numerical models of circumstellar disks and envelopes.; I have obtained near-IR adaptive optics imaging polarimetry and mid-IR imaging of a large sample of Herbig Ae/Be stars; 110 targets were observed with AO polarimetry and 61 with mid-IR imaging. Of these stars, 40 are found to have extended polarized nebulosity arising from scattered light. The dust geometry is highly variable, ranging from circumstellar disks to envelopes split by bipolar outflow cavities to complex arcs and lanes of dust spiraling around and between stars. I present detailed studies of a subset of these objects, including laser guide star AO observations of disks and envelopes around the stars LkHalpha 198 and LkHalpha 233; the discovery of the first resolved edge-on circumstellar disk around a Herbig Ae/Be star, PDS 144 N; and integral field spectroscopy of a narrowly collimated bipolar outflow from LkHalpha 233. I conclude by discussing future prospects for advances in the studies of circumstellar disks with the coming generation of high contrast instruments.