Volume 579, July 2015
|Number of page(s)||4|
|Published online||19 June 2015|
Mercapto radical (SH) in translucent interstellar clouds⋆
1 Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
2 Instituto de Astronomia, Universidad Catolica del Norte, Av. Angamos 0610, Antofagasta, Chile
3 Pulkovo Observatory, Pulkovskoe Shosse 65, 196140 Saint-Petersburg, Russia
4 Center for Astronomy, Nicholas Copernicus University, Gagarina 11, 87-100 Toruń, Poland
Received: 7 May 2015
Accepted: 24 May 2015
We present the first detection of rotationally resolved electronic transitions of the mercapto radical (SH) in the near-ultraviolet in translucent interstellar clouds. Observational data acquired by the Ultraviolet and Visual Echelle Spectrograph of the Very Large Telescope were used to search for the near-ultraviolet absorption spectra of SH. Two weak absorption features at ~3242.40 and 3240.66 Å, assigned as the pP11(3/2) and the (qP21(3/2) + qQ11(3/2)) doublet transitions in the A2Σ+–X2Π (0, 0) band of SH, respectively, were identified in the averaged spectrum of four selected lines of sight: HD 73882, HD 78344, HD 80077, and HD 154368. These features are weak, but can be identified within a 3σ detection limit, and are found in other published data sets as well. We compiled a set of line positions and oscillator strengths of SH to facilitate the data analysis. We derived an averaged value of the SH column density, ~1.5 ± 0.3 × 1013 cm-2, that is most likely representative for the magnitude of SH column densities in individual SH-rich translucent clouds. This value is also consistent with predictions from models for C-type shocks and turbulent dissipation regions with typical translucent cloud conditions.
Key words: ISM: clouds / ISM: molecules / ISM: lines and bands / ultraviolet: ISM
© ESO, 2015
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