EPoS Contribution

A new population of protostars discovered by Herschel

Amelia Stutz
MPIA, Heidelberg, Germany
We present a newly discovered Herschel--detected class of very red protostars found in the Herschel Orion Protostar Survey (HOPS). In contrast to the known Orion protostars targeted with HOPS, the new sources are undetected or very faint in the Spitzer 24 um imaging. A subset of these sources is redder than any of the known Orion Class 0 protostars, and appear similar in their 70 um to 24 um colors to the most extreme Class 0 objects known. These new Orion protostars are likely to be in a very early and short lived stage of protostellar evolution. As a sample of extremely red sources at a common distance, they represent an important new population of protostars. The majority of these reddest sources exhibit associated IRAC 4.5, and 5.8 um extended emission that suggests the presence of an outflow, confirming their protostellar nature. In addition, many of these sources are located within classical filaments as traced by Spitzer absorption features and APEX 870 um dust emission maps. Fits of the broad--band SEDs to radiative transfer models of protostars suggest that the extremely red 70 um to 24 um colors result from a combination of nearly edge--on viewing angles and high envelope infall rates. We analyze the properties of the filaments from which these sources form using sub--mm and IRAM 30 m N2H+ measurements. Finally, we present the initial results of a search for outflows using IRAM 30 m CO maps. As a population of cold protostars detected by Herschel but not Spitzer, the new sources (PBRS) extend the Spitzer--identified sample to earlier stages of envelope evolution, allowing the most complete census yet of the Orion protostellar population.
T. Megeath, J. Tobin, W. Fischer, T. Henning, J. Di Francesco, B. Ali, & HOPS team