EPoS Contribution
EPoS Contribution
HOPS: Testing the Low-Mass Star Formation Paradigm in the Orion Molecular Clouds

Will Fischer
University of Toledo, Toledo, USA
A comprehensive understanding of the evolution of low-mass protostars, from the earliest phases of collapse to the dissipation of the infalling envelope, remains elusive. In particular, what processes control the infall of material from the protostellar envelope? To what extent is the accretion of envelope material onto the central protostar episodic? How does clustering affect the evolution of low-mass protostars? These questions can be addressed with a detailed census of the properties of protostellar envelopes in a large, environmentally diverse star-forming region. The Herschel Orion Protostar Survey (HOPS) is furthering this goal by observing 330 protostellar candidates in the Orion molecular clouds, combining Herschel 70 and 160 um photometry and 50--200 um spectroscopy, Spitzer 3.6--40 um photometry and spectroscopy, 1.6 um HST imaging, and sub-mm APEX imaging. The sample encompasses all phases of protostellar evolution, from the beginning of Class 0 through the end of Class I, 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 um SEDs of the 330 protostars to determine their envelope densities, cavity opening angles, inclinations, and luminosities. Consistent with previous studies of star-forming regions closer than Orion, we find a spread in luminosity of three orders of magnitude at each evolutionary stage, including sources as faint as 0.1 Lsun. After accounting for a sample of young, faint Class 0 protostars discovered in the Herschel images, we find evidence for a longer Class 0 phase than previously estimated. We compare the results across a variety of environments, from clusters to groups to isolation, to understand the impact of environment on protostellar evolution. In particular, we find that protostars are on average more luminous in more crowded regions and regions of greater gas column density. Finally, we use multiepoch, multiwavelength spectroscopy and photometry to argue that a recently announced outbursting protostar in the HOPS sample has transitioned to the FU Orionis regime.
T. Megeath, U. Toledo, USA
J. Tobin, NRAO, USA
B. Ali, NHSC/IPAC/Caltech, USA
A. Stutz, MPIA, Germany
M. Osorio, IAA, Spain
D. Watson, U. Rochester, USA
P. Manoj, U. Rochester, USA
R. Vavrek, HSC, Spain