Volume 569, September 2014
|Number of page(s)||5|
|Published online||19 September 2014|
Revised spectroscopic parameters of SH+ from ALMA and IRAM 30 m observations⋆,⋆⋆,⋆⋆⋆
I. Physikalisches Institut, Universität zu Köln,
Zülpicher Str. 77, 50937
2 Instituto de Ciencias de Materiales de Madrid (CSIC), 28049 Cantoblanco, Madrid, Spain
3 IRAM, 300 rue de la Piscine, 38406 Saint Martin d’Hères, France
4 CNRS UMR 8112, LERMA, Observatoire de Paris, École Normale Supérieure and Université Pierre et Marie Curie, 75014 Paris, France
5 Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
6 CNRS, LAB, UMR 5804, 33270 Floirac, France
7 Université de Bordeaux, LAB, UMR 5804, 33270 Floirac, France
Accepted: 3 September 2014
Hydrides represent the first steps of interstellar chemistry. Sulfanylium (SH+), in particular, is a key tracer of energetic processes. We used ALMA and the IRAM 30 m telescope to search for the lowest frequency rotational lines of SH+ toward the Orion Bar, the prototypical photo-dissociation region illuminated by a strong UV radiation field. On the basis of previous Herschel/HIFI observations of SH+, we expected to detect emission of the two SH+ hyperfine structure (HFS) components of the NJ = 10−01 fine structure (FS) component near 346 GHz. While we did not observe any lines at the frequencies predicted from laboratory data, we detected two emission lines, each ~15 MHz above the SH+ predictions and with relative intensities and HFS splitting expected for SH+. The rest frequencies of the two newly detected lines are more compatible with the remainder of the SH+ laboratory data than the single line measured in the laboratory near 346 GHz and previously attributed to SH+. Therefore, we assign these new features to the two SH+ HFS components of the NJ = 10−01 FS component and re-determine its spectroscopic parameters, which will be useful for future observations of SH+, in particular if its lowest frequency FS components are studied. Our observations demonstrate the suitability of these lines for SH+ searches at frequencies easily accessible from the ground.
Key words: molecular data / line: identification / ISM: molecules / radio lines: ISM / ISM: individual objects: Orion Bar
This paper makes use of the following ALMA data: ADS/JAO.ALMA#2012.1.00352.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ.
This paper makes use of observations obtained with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2014
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