Author(s): , , ,
Institution(s): 1. Korea Astronomy and Space Science Institute, 2. Max Planck Institute for Astronomy, 3. National Astronomical Observatory of Japan
One of the principal goals of recent star formation studies is to understand the evolution of protostars. Recently, extremely cold sources, called PACS Bright Red Sources (PBRS), have been identified via Herschel dust continuum observations in the Orion molecular cloud complex. The PBRS are the objects with very red colors in 24 μm to 70 μm and proposed as very young Class 0 protostars embedded in dense envelopes. We present observations of the HDCO and H2CO emission towards a sample of 11 PBRS and 4 previously identified Class 0 protostars (non-PBRS) in Orion A and B clouds. We derive the column densities of HDCO and H2CO and estimate the degree of deuteration in H2CO ([HDCO]/[H2CO]) between 0.03 and 0.31. While mean [HDCO]/[H2CO] ratios of both PBRS and non-PBRS are similar (~ 0.1), the mean [HDCO]/[H2CO] ratio of highly deuterated PBRS is three times higher than the ratio of non-PBRS. The variation of the deuterium fractionation of the PBRS sample implies that the PBRS with high [HDCO]/[H2CO] ratios are in the very earliest stage of star formation or they have a different formation history.