* Astronomy

Title: The Herschel Orion Protostar Survey (HOPS)
Authors: Megeath, S. Thomas; Fischer, W.; Ali, B.; Allen, L.; Poteet, C.; Watson, D.; Wilson, T

A complete description of the formation of stellar systems, from the initial collapse of a cloud core to the emergence of planets, requires a detailed understanding of the evolution of protostars. The largest sample of protostars in the nearest 500 pc is in the Orion molecular clouds where over 400 have been identified with Spitzer. These protostars are forming in a range of environments from dense clusters to near isolation. The Herschel Orion Protostar Survey (HOPS) is a 200-hour open-time key project that will use PACS to observe 278 of these protostars, encompassing a wide range of source luminosities, evolutionary phases, and environments. Deep imaging at the highest resolution possible with PACS will be obtained for the full HOPS sample at 70 and 160 um. These data will sample the peak of the thermal emission from the protostellar envelope, enabling the determination of bolometric luminosities, envelope morphologies, and, with the use of radiative transfer codes, envelope densities and infall rates. PACS spectra from 55 to 210 um will also be obtained for 36 of the protostars. Lines of water vapor, OH, O, and CO in these spectra will allow estimates of accretion rates through the envelopes and onto the central objects as well as outflow rates through the envelope cavities. The PACS data will be complemented by existing Spitzer photometry and spectra, an ongoing near-IR imaging campaign with the HST, VLT, IRTF, and Magellan, and data from numerous other ground-based telescopes. We demonstrate the power of this approach with initial models of several Orion protostars using existing Spitzer and HST data. The HOPS images and spectra will compose the first systematic survey of hundreds of protostars in a single molecular cloud, a necessary step in disentangling the complexities of protostellar evolution.

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