Reconstructing the density and temperature structure of prestellar cores fromHerscheldata: A case study for B68 and L1689B

Abstract

Utilizing multiwavelength dust emission maps acquired with Herschel, we reconstruct local volume density and dust temperature profiles for the prestellar cores B68 and L1689B using an inverse-Abel transform-based technique. We present intrinsic radial dust temperature profiles of starless cores directly from dust continuum emission maps disentangling the effect of temperature variations along the line of sight, which were previously limited to the radiative transfer calculations. The reconstructed dust temperature profiles show a significant drop in the core center, a flat inner part, and a rising outward trend until the background cloud temperature is reached. The central beam-averaged dust temperatures obtained for B68 and L1689B are 9.3 ± 0.5 K and 9.8 ± 0.5 K, respectively, which are lower than the temperatures of 11.3 K and 11.6 K obtained from direct SED fitting. The best mass estimates derived by integrating the volume density profiles of B68 and L1689B are 1.6 M and 11 M , respectively. Comparing our results for B68 with the near-infrared extinction studies, we find that the dust opacity law adopted by the HGBS project, κ λ = 0.1 × agrees to within 50% with the dust extinction constraints.

A census of dense cores in the Taurus L1495 cloud from theHerschelGould Belt Survey

“…The flux densities used in SED fitting are presented in Table B1. For this exercise, sources were assumed to be isothermal and have a wavelength variation of opacity of the form (Hildebrand 1983;Roy et al 2014):…”

“…Such a correlation might be expected based on a model in which the dust is heated by the interstellar radiation field (ISRF). Large column densities then provide more shielding, resulting in cooler dust (Evans et al 2001;Stamatellos et al 2007;Roy et al 2014). But could this correlation be an artifact, induced by a degeneracy between mass and temperature in the SED measurement model?…”

“…For the present observations, however, the Herschel wavelengths bracket the peak of the modified blackbody function for all of the core temperatures likely to be encountered. It is true that temperature gradients within cores can also give rise to mass biases (and hence column density biases) when using simple SED fitting, but these biases are typically at the < ∼ 30% level (see, for example, Roy et al 2014;Könyves et al 2015) and not sufficient to produce the correlation apparent in Fig. 3.…”

“…Herschel observations have provided strong indications of an evolutionary link between filaments and cores (André et al 2010(André et al , 2014, and so it is of interest to ask what fraction of prestellar cores lies on filaments. In this regard Polychroni et al (2013) found that 71% of prestellar cores in the L1641 cloud of Orion A were located on filaments with AV > 5 mag, leaving a substantial fraction that were not.…”

“…Most definitions are observationally based and therefore quite subjective. To provide a context for subsequent discussion, we adopt as a working definition the one given by André et al (2014), i.e., "any elongated ISM structure with an aspect ratio larger than ∼ 5-10 that is significantly overdense with respect to its surroundings," but qualify it further by specifying that the elongated structure must be visible directly in a column density image that has not been spatially filtered.…”