Interstellar nitrile anions: Detection of C3N− and C5N− in TMC-1

We report on the first detection of C3N− and C5N− towards the cold dark core TMC-1 in the Taurus region, using the Yebes 40 m telescope. The observed C3N/C3N− and C5N/C5N− abundance ratios are ∼140 and ∼2, respectively; that is similar to those found in the circumstellar envelope of the carbon-rich star IRC +10216. Although the formation mechanisms for the neutrals are different in interstellar (ion-neutral reactions) and circumstellar clouds (photodissociation and radical-neutral reactions), the similarity of the C3N/C3N− and C5N/C5N− abundance ratios strongly suggests a common chemical path for the formation of these anions in interstellar and circumstellar clouds. We discuss the role of radiative electronic attachment, reactions between N atoms and carbon chain anions Cn−, and that of H− reactions with HC3N and HC5N as possible routes to form CnN−. The detection of C5N− in TMC-1 gives strong support for assigning to this anion the lines found in IRC +10216, as it excludes the possibility of a metal-bearing species, or a vibrationally excited state. New sets of rotational parameters have been derived from the observed frequencies in TMC-1 and IRC +10216 for C5N− and the neutral radical C5N.

A 3D view of the Taurus star-forming region by Gaia and Herschel

Context. Taurus represents an ideal region to study the three-dimensional distribution of the young stellar population and relate it to the associated molecular cloud. Aims. The second Gaia data release (DR2) enables us to investigate the Taurus complex in three dimensions, starting from a previously defined robust membership. The molecular cloud structured in filaments can be traced in emission using the public far-infrared maps from Herschel. Methods. From a compiled catalog of spectroscopically confirmed members, we analyze the 283 sources with reliable parallax and proper motions in the Gaia DR2 archive. We fit the distribution of parallaxes and proper motions with multiple populations described by multivariate Gaussians. We compute the cartesian Galactic coordinates (X,Y,Z) and, for the populations associated with the main cloud, also the galactic space velocity (U,V,W). We discuss the spatial distribution of the populations in relation to the structure of the filamentary molecular cloud traced by Herschel. Results. We discover the presence of six populations which are all well defined in parallax and proper motions, with the only exception being Taurus D. The derived distances range between ~130 and ~160 pc. We do not find a unique relation between stellar population and the associated molecular cloud: while the stellar population seems to be on the cloud surface, both lying at similar distances, this is not the case when the molecular cloud is structured in filaments. Taurus B is probably moving in the direction of Taurus A, while Taurus E appears to be moving towards them. Conclusions. The Taurus region is the result of a complex star formation history which most probably occurred in clumpy and filamentary structures that are evolving independently.

SCUBA2 observations of prestellar cores

We show data from the SCUBA2 camera on JCMT, of molecular clouds. We focus on starless cores within the clouds. We present data of the Taurus region and show how the environment is affecting some cores' appearance in this region. We compare the SCUBA2 data with Herschel data and discuss the sensitivity of SCUBA2 to surface brightness in the sub-millimetre. We show how this leads to its ability to pick out the densest cores at a given temperature. Hence SCUBA2 preferentially picks out gravitationally bound pre-stellar cores. We discuss the effects of the magnetic field, and how this lends support to a model for the formation and evolution of cores in filamentary molecular clouds.