The Earliest Phases of Star formation (EPoS) observed withHerschel: the dust temperature and density distributions of B68

Abstract

Context. Isolated starless cores within molecular clouds can be used as a testbed to investigate the conditions prior to the onset of fragmentation and gravitational proto-stellar collapse. Aims. We aim to determine the distribution of the dust temperature and the density of the starless core B68. Methods. In the framework of the Herschel guaranteed-time key programme "The Earliest Phases of Star formation" (EPoS), we have imaged B68 between 100 and 500 μm. Ancillary data at (sub)millimetre wavelengths, spectral line maps of the 12 CO (2-1), and 13 CO (2-1) transitions, as well as an NIR extinction map were added to the analysis. We employed a ray-tracing algorithm to derive the 2D mid-plane dust temperature and volume density distribution without suffering from the line-of-sight averaging effects of simple SED fitting procedures. Additional 3D radiative transfer calculations were employed to investigate the connection between the external irradiation and the peculiar crescent-shaped morphology found in the FIR maps. Results. For the first time, we spatially resolve the dust temperature and density distribution of B68, convolved to a beam size of 36. 4. We find a temperature gradient dropping from (16.7 ) × 10 5 cm −3 . B68 has a mass of 3.1 M of material with A K > 0.2 mag for an assumed distance of 150 pc. We detect a compact source in the southeastern trunk, which is also seen in extinction and CO. At 100 and 160 μm, we observe a crescent of enhanced emission to the south. Conclusions. The dust temperature profile of B68 agrees well with previous estimates. We find the radial density distribution from the edge of the inner plateau outward to be n H ∝ r −3.5 . Such a steep profile can arise from either or both of the following: external irradiation with a significant UV contribution or the fragmentation of filamentary structures. Our 3D radiative transfer model of an externally irradiated core by an anisotropic ISRF reproduces the crescent morphology seen at 100 and 160 μm. Our CO observations show that B68 is part of a chain of globules in both space and velocity, which may indicate that it was once part of a filament that dispersed. We also resolve a new compact source in the southeastern trunk and find that it is slightly shifted in centroid velocity from B68, lending qualitative support to core collision scenarios.

Deuteration of ammonia in the starless core Ophiuchus/H-MM1

“…The fitted T C overestimates the massaveraged dust temperature because of line-of-sight temperature variations. This effect is more marked towards the centre of a starless core than on the outskirts of the core (Nielbock et al 2012;Suutarinen et al 2013). …”

AHERSCHELAND APEX CENSUS OF THE REDDEST SOURCES IN ORION: SEARCHING FOR THE YOUNGEST PROTOSTARS

“…We expect that the assumption of a single LOS temperature will cause an underestimate of the source masses (e.g., Nielbock et al 2012;Launhardt et al 2013). However, radiative transfer models have large ambiguities in the assumed source temperature and density structure, leading to mass estimates that are strongly model-dependent.…”

Radio and infrared study of the star-forming region IRAS 20286+4105

“…Following the procedure outlined in Battersby et al (2011), Nielbock et al (2012, Launhardt et al (2013), andMallick et al (2015), a pixel-by-pixel modeling of this dust emission with a gray body/modified blackbody is adopted in order to generate temperature and column density maps of the region of our interest. For the preliminary steps, the Herschel data compatible software HIPE 5 is used.…”

“…Masses of these two clumps associated with IRAS 20286+4105 are estimated from the derived column density map using the following expression from Nielbock et al (2012).…”