A (sub)millimetre study of dense cores in Orion B9

Abstract

We aim to further constrain the properties and evolutionary stages of dense cores in Orion B9. The central part of Orion B9 was mapped at 350 micron with APEX/SABOCA. A sample of nine cores in the region were observed in C17O(2-1), H13CO+(4-3) (towards 3 sources), DCO+(4-3), N2H+(3-2), and N2D+(3-2) with APEX/SHFI. These data are used in conjunction with our previous APEX/LABOCA 870-micron dust continuum data. Many of the LABOCA cores show evidence of substructure in the higher-resolution SABOCA image. In particular, we report on the discovery of multiple very low-mass condensations in the prestellar core SMM 6. Based on the 350-to-870 micron flux density ratios, we determine dust temperatures of ~7.9-10.8 K, and dust emissivity indices of ~0.5-1.8. The CO depletion factors are in the range ~1.6-10.8. The degree of deuteration in N2H+ is ~0.04-0.99, where the highest value (seen towards the prestellar core SMM 1) is, to our knowledge, the most extreme level of N2H+ deuteration reported so far. The level of HCO+ deuteration is about 1-2%. We also detected D2CO towards two sources. The detection of subcondensations within SMM 6 shows that core fragmentation can already take place during the prestellar phase. The origin of this substructure is likely caused by thermal Jeans fragmentation of the elongated parent core. A low depletion factor and the presence of gas-phase D2CO in SMM 1 suggest that the core chemistry is affected by the nearby outflow. The very high N2H+ deuteration in SMM 1 is likely to be remnant of the earlier CO-depleted phase.