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

Abstract

Context. Studies of dense molecular-cloud cores at (sub)millimetre wavelengths are needed to understand the early stages of star formation. Aims. We aim to further constrain the properties and evolutionary stages of dense cores in Orion B9. The prime objective of this study is to examine the dust emission of the cores near the peak of their spectral energy distributions, and to determine the degrees of CO depletion, deuterium fractionation, and ionisation. Methods. The central part of Orion B9 was mapped at 350 μm with APEX/SABOCA. A sample of nine cores in the region were observed in C 17 O(2−1), H 13 CO + (4−3) (towards 3 sources), DCO + (4−3), N 2 H + (3−2), and N 2 D + (3−2) with APEX/SHFI. These data are used in conjunction with our previous APEX/LABOCA 870-μm dust continuum data. Results. All the LABOCA cores in the region covered by our SABOCA map were detected at 350 μm. The strongest 350 μm emission is seen towards the Class 0 candidate SMM 3. 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 μm flux density ratios, we determine dust temperatures of T dust 7.9−10.8 K, and dust emissivity indices of β ∼ 0.5−1.8. The CO depletion factors are in the range f D ∼ 1.6−10.8. The degree of deuteration in N 2 H + 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 N 2 H + deuteration reported so far. The level of HCO + deuteration is about 1-2%. The fractional ionisation and cosmic-ray ionisation rate of H 2 could be determined only towards two sources with the lower limits of ∼2−6 × 10 −8 and ∼2.6 × 10 −17 −4.8 × 10 −16 s −1 , respectively. We also detected D 2 CO towards two sources. Conclusions. The detected protostellar cores are classified as Class 0 objects, in agreement with our previous SED results. 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. Varying levels of f D and deuteration among the cores suggest that they are evolving chemically at different rates. A low f D value and the presence of gas-phase D 2 CO in SMM 1 suggest that the core chemistry is affected by the nearby outflow. The very high N 2 H + deuteration in SMM 1 is likely to be remnant of the earlier CO-depleted phase.

CHARACTERIZING THE YOUNGESTHERSCHEL-DETECTED PROTOSTARS. I. ENVELOPE STRUCTURE REVEALED BY CARMA DUST CONTINUUM OBSERVATIONS

“…The envelope as observed at 870 μm is extended to the east and at 350 μm there are a few sub-peaks associated with the extended 870 μm emission (Miettinen et al 2012). We do not, however, detect 2.9 mm continuum emission from these sub-peaks, indicating that they do not harbor compact protostellar sources.…”

“…Much like 093005, its only detection shortward of 24 μm is at 4.5 μm, where there is a small feature offset from the location of the protostar, indicative of shocked H 2 emission (Miettinen et al 2012;Stutz et al 2013).…”

13CO and C18OJ = 2–1 mapping of the environment of the Class 0 protostellar core SMM 3 in Orion B9

“…Using this temperature, the core mass was determined to be 7.8±1.6 M , and its volume-averaged H 2 number density was estimated to be 1.1 ± 0.2 × 10 5 cm −3 . In the SABOCA 350-μm mapping of Orion B9 by Miettinen et al (2012;Paper III), SMM 3 was found to be by far the strongest source in the mapped area (S 350 5.4 Jy). We also found that it contains two subfragments, or condensations (we called SMM 3b and 3c), lying about 36 −51 in projection from the central protostar.…”

Chemistry of TMC-1 with multiply deuterated species and spin chemistry of H 2 , H 2 + , H 3 + and their isotopologues

“…+ (Miettinen et al 2012), NHD2 ; -towards low-mass and high-mass protostars: D2CO, HDCO (Bergman et al 2011), DCOOCH3 (Demyk et al 2010;Margulès et al 2010), HDO (Coutens et al 2012, D2O , OD (Parise et al 2012); -in protoplanetary disks: DCN, DCO + (van Dishoeck et al 2003;Guilloteau et al 2006;Qi et al 2008;Öberg et al 2015), N2D…”