Protostars at Low Extinction in Orion A

TL;DR

This study investigates low extinction protostars in Orion A, using multi-wavelength data to confirm their nature, revealing that only a subset are true protostars often lacking dense core associations.

Contribution

It provides a detailed analysis of low extinction protostellar candidates, distinguishing true protostars from contaminants using high-resolution extinction maps and multi-wavelength observations.

Findings

10 out of 44 candidates are confirmed protostars

Most confirmed protostars lack dense core associations

Remaining candidates are mostly evolved objects or contaminants

Abstract

In the list of young stellar objects compiled by Megeath et al. (2012) for the Orion A molecular cloud, only 44 out of 1208 sources found projected onto low extinction (Ak<0.8 mag) gas are identified as protostars. These objects are puzzling because protostars are not typically expected to be associated with extended low extinction material. Here, we use high resolution extinction maps generated from Herschel data, optical/infrared and Spitzer Space Telescope photometry and spectroscopy of the low extinction protostellar candidate sources to determine if they are likely true protostellar sources or contaminants. Out of 44 candidate objects, we determine that 10 sources are likely protostars, with the rest being more evolved young stellar objects (18), galaxies (4), false detections of nebulosity and cloud edges (9), or real sources for which more data are required to ascertain their nature (3). We find none of the confirmed protostars to be associated with recognizable dense cores and we briefly discuss possible origins for these orphaned objects.