Results from HOPS: A Multiwavelength Census of Orion Protostars

TL;DR

This study uses Herschel and Spitzer data to analyze 328 protostars in Orion, revealing diverse properties, luminosity distributions, and new sources, advancing understanding of star formation in different environments.

Contribution

First comprehensive multiwavelength survey of Orion protostars with detailed SED modeling, revealing luminosity spread and new sources, including the least luminous FU Ori star with an envelope.

Findings

Luminosity varies over several orders of magnitude at all stages.

Median luminosity remains constant across evolutionary stages.

Detected over 100 new Herschel sources, possibly filling a known observational gap.

Abstract

Surveys with the Spitzer and Herschel space observatories are now enabling the discovery and characterization of large samples of protostars in 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 Protostar Survey (HOPS), which targets 328 Spitzer-identified protostars in 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 protostars to estimate their envelope densities, cavity opening angles, inclinations, and total luminosities. After correcting the bolometric luminosities and temperatures of the sources for foreground extinction and inclination, we find a spread of several orders of magnitude in luminosity at all evolutionary states, a constant median luminosity over the more evolved stages, and a possible deficit of high-inclination, rapidly infalling envelopes 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.