Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 1H018

The Discovery of Extremely Young Protostars in Orion with Herschel and APEX

Stutz, Amelia (MPIA)
Tobin, John (NRAO)
Stanke, Thomas (ESO)
Megeath, Tom (U. of Toledo, Ohio)
Fischer, Will (U. of Toledo, Ohio)
Robitaille, Thomas (MPIA)
Henning, Thomas (MPIA)
Ali, Babar (IPAC)
Di Francesco, James (CNRC)
Furlan, Elise (IPAC)
Osorio, Mayra (IAA)
Team, HOPS (ALL)

We perform a census of the reddest, and potentially youngest, protostars in the Orion molecular clouds using 24 um - 870 um imaging obtained with the Spitzer, Herschel, and APEX telescopes as part of the Herschel Orion Protostar Survey (HOPS). We find a sample of 15 new extremely red protostar candidates that can reliably identified as protostars (Stutz et al., 2013). Taking the previously known sample of 300 Spitzer protostars and the new sample of 15 Herschel identified protostars together, we find 18 extremely red protostars (i.e., log λFλ70 / λFλ24 > 1.65). These are the reddest protostars known in Orion and we name them \"PACS Bright Red sources\", or PBRS. Our analysis reveals that the PBRs sample is composed of Class 0 like sources with very red spectral energy distributions (SEDs; Tbol < 45 K) and large sub-millimeter fluxes (Lsmm/Lbol > 0.6%). Modified blackbody fits to the SEDs provide lower limits to the envelope masses of 0.2 Msun - 2 Msun and luminosities of 0.7 Lsun - 10 Lsun. Based on these properties, and a comparison of the SEDs with radiative transfer models of protostars, we conclude that the PBRs are most likely extreme Class 0 objects distinguished by higher than typical envelope densities and possibly high mass infall rates. We estimate the ages of the PBRs to be between 5000 and 25000 years. We find that the fraction of PBRS is more than 5 times higher in the Orion B cloud than in Orion A; this may be due to differences in the star formation histories or in the star forming environment.

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