PI: Jayadev Rajagopal, CTIO/NOAO, firstname.lastname@example.org
Address: Casilla 603, La Serena, Chile
CoI: Eric J. Bakker, New Mexico Tech / Magdalena Ridge Observatory
Title: The circumbinary disk and environs of post-AGB stars at high resolution and deep contrast
Abstract: HR 4049 is a prototype for a class of post-AGB stars which are single-line spectroscopic binaries showing extreme metal-deficiency in their photospheres and a large IR excess. These properties are attributed to the presence of a stable circumbinary dust and gas disk in a Keplerian orbit. Currently, only the hottest inner regions of this disk has been detected through interferometric techniques. However IR SEDs, CO mm wave measurements and likely disk-formation scenarios suggest more extended circumstellar structure. In some cases, like the Red Rectangle, a bipolar nebula is known to exist. The formation and structure of the disk and any extended nebula are very poorly understood. Here we propose high resolution imaging in the near-IR of the circumstellar environment of HR 4049 and a small sample of very similar post-AGB binaries with the Gemini AO imager, NICI. We will measure the extent of the Keplerian disk, confirm the existence, and determine the structure of the faint extended nebula by masking out the very bright inner rim and central binary. The orientation of the disk will probe the interplay of angular momentum between the binary and the disk, a key to the formation and continued stability of a dust disk around the binary. The existence and shape of the outer nebulae will directly test various models for the formation mechanism of the disk. The disk and nebula are also key components in the evolution of these objects to Planetary Nebulae.
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