Volume 597, January 2017
|Number of page(s)||16|
|Section||Interstellar and circumstellar matter|
|Published online||03 January 2017|
A correlation between chemistry, polarization, and dust properties in the Pipe nebula starless core FeSt 1-457⋆
1 Institut de Ciències de l’Espai, (CSIC-IEEC), Campus UAB, Carrer de Can Magrans, S/N, 08193 Cerdanyola del Vallès, Catalonia, Spain
2 Dept. de Física Quàntica i Astrofísica (formerly Astronomia i Meteorologia), Institut de Ciències del Cosmos (ICCUB) Universitat de Barcelona (IEEC-UB), Martí Franquès 1, 08028 Barcelona, Spain The ICCUB is a CSIC-Associated Unit through the Institut de Ciències de l’Espai (ICE)
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
4 Observatorio Astronómico Nacional, Alfonso XII 3, 28014 Madrid, Spain
5 Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, PO Box 3-72, 58090 Morelia, Michoacan, Mexico
6 Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141, 106 Taipei, Taiwan
7 Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
8 INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
9 Laboratoire Univers et Particules de Montpellier, UMR 5299 du CNRS, Université de Montpellier II, place E. Bataillon, CC 072, 34095 Montpellier, France
Received: 30 March 2016
Accepted: 3 October 2016
Pre-stellar cores within molecular clouds provide the very initial conditions in which stars are formed. FeSt 1-457 is a prototypical starless core and the most chemically evolved among those isolated, embedded in the most pristine part of the Pipe nebula, the bowl. We use the IRAM 30 m telescope and the PdBI to study the chemical and physical properties of the starless core FeSt 1-457 (Core 109) in the Pipe nebula. We fit the hyperfine structure of the N2H+ (1−0) IRAM 30 m data. This allowed us to measure with high precision the velocity field, line widths and opacity and derive the excitation temperature and column density in the core. We used a modified Bonnor-Ebert sphere model adding a temperature gradient towards the center to fit the 1.2 mm continuum emission and visual extinction maps. Using this model, we have estimated the abundances of the N2H+ and the rest of molecular lines detected in the 30 GHz wide line survey performed at 3 mm with IRAM 30 m using ARTIST software. The core presents a rich chemistry with emission from early (C3H2, HCN, CS) and late-time molecules (e.g., N2H+), with a clear chemical spatial differentiation for nitrogen (centrally peaked), oxygen (peaking to the southwest) and sulfurated molecules (peaking to the east). For most of the molecules detected (HCN, HCO+, CH3OH, CS, SO, 13CO and C18O), abundances are best fit with three values, presenting a clear decrease of abundance of at least one or two orders of magnitude towards the center of the core. The Bonnor-Ebert analysis indicates the core is gravitationally unstable and the magnetic field is not strong enough to avoid the collapse. Depletion of molecules onto the dust grains occurs at the interior of the core, where dust grain growth and dust depolarization also occurs. This suggests that these properties may be related. On the other hand, some molecules exhibit asymmetries in their integrated emission maps, which appear to be correlated with a previously reported submillimetre polarization asymmetry. These asymmetries could be due to a stronger interstellar radiation field in the western side of the core.
Key words: stars: formation / ISM: individual objects: FeSt 1-457 / ISM: molecules / radiative transfer
The fits files for Figs. 1, 4, and 5 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/597/A74
© ESO, 2017
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