Results from HOPS: A Multiwavelength Census of Orion Protostars

Surveys with the Spitzer and Herschel space observatoriesare now enabling the discovery and characterization of large samples of protostarsin nearby molecular clouds, providing the observational basis for a detailed understanding of star formation in diverse environments. We are pursuing this goal with the Herschel Orion ProtostarSurvey (HOPS), which targets 328 Spitzer-identified protostarsin the Orion molecular clouds, the largest star-forming region in the nearest 500 pc. The sample encompasses all phases of protostellar evolution and a wide range of formation environments, from dense clusters to relative isolation. With a grid of radiative transfer models, we fit the 1-870 micron spectral energy distributions(SEDs) of the protostarsto estimate their envelope densities, cavity opening angles, inclinations, and total luminosities. After correcting the bolometric luminositiesand temperatures of the sources for foreground extinction and inclination, we find a spread of several orders of magnitude in luminosityat all evolutionary states, a constant median luminosityover the more evolved stages, and a possible deficit of high-inclination, rapidly infallingenvelopes among the Spitzer-identified sample. We have detected over 100 new sources in the Herschel images; some of them may fill this deficit. We also report results from modeling the pre- and post-outburst 1-870 micron SEDs of V2775 Ori (HOPS 223), a known FU Orionis outburster in the sample. It is the least luminous FU Ori star with a protostellar envelope.