Mercapto radical (SH) in translucent interstellar clouds
Abstract
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.
Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under programs 092.C-0019(A) and 082.C-0566(A).- Publication:
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Astronomy and Astrophysics
- Pub Date:
- July 2015
- DOI:
- 10.1051/0004-6361/201526488
- Bibcode:
- 2015A&A...579L...1Z
- Keywords:
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- ISM: clouds;
- ISM: molecules;
- ISM: lines and bands;
- ultraviolet: ISM