Silicon monosulfide, SiS, is a very abundant molecule in the inner regions
of the circumstellar envelop of IRC+10216 (CW Leo) where it is thought to
be the progenitor of much of the Si-chemistry. It was reported first by
M. Morris, W. Gilmore, P. Palmer, B. E. Turner, and B. Zuckerman,
Detection of Interstellar SiS and a Study of the IRC +10216 Molecular Envelope
Astrophys. J. 199, L47L51 (1975).
The first paper, mentioned in the previous paragraph, also reports on the
tentative detection of SiS toward Sgr B2. In the meantime, there have been
several reports on SiS in massive star-forming regions.
A total of seven rare isotopic species has been detected since.
These involve 29SiS and Si34S:
L. E. B. Johansson, C. Andersson, J. Ellder, P. Friberg, Å. Hjalmarson, B. Höglund, W. M. Irvine, H. Olofsson, and G. Rydbeck,
Spectral Scan of Orion A and IRC+10216 from 72 to 91 GHz
Astron. Astrophys. 130, 227256 (1984);
L. M. Ziurys, D. P. Clemens, R. J. Saykally, M. Colvin, H. F. Schaefer,
A Search for Interstellar Silicon Nitride
Astrophys. J. 281, 219224 (1984);
C. Kahane, J. Gomez-Gonzalez, J. Cernicharo, and M. Guélin,
Carbon, Nitrogen, Sulfur and Silicon Isotopic Ratios in the Envelope of IRC +10216
Astron. Astrophys. 190, 167177 (1988);
29Si34S and 30Si34S:
J. Cernicharo, M. Guélin, and C. Kahane,
A λ 2 mm Molecular Line Survey of the C-Star Envelope IRC +10216
Astron. Astrophys. Suppl. 142, 181215 (2000);
R. Mauersberger, U. Ott, C. Henkel, J. Cernicharo, and R. Gallino,
The Abundance of 36S in IRC +10216 and its Production in the Galaxy
Astron. Astrophys. 426, 219227 (2004).
Maser activity in v = 0 of the
main isotopic species has been reported first by
C. Henkel, H. E. Matthews, and M. Morris,
SiS Maser Emission from IRC +10216
Astrophys. J. 267, 184190 (1983).
J. P. Fonfría Expósito, M. Agúndez, B. Tercero, J. R. Pardo, and J. Cernicharo
High-J v = 0 SiS Maser Emission in IRC +10216: A New Case of Infrared Overlaps
Astrophys. J. 646, L127L130 (2006).
Transitions J = 11 10, 14 13, and 15 14 were found to be masing.
Vibrationally excited SiS has been detected by
B. E. Turner,
Detection of Vibrationally Excited SiS in IRC +10216
Astron. Astrophys. 183, L23L26 (1987).
L. Velilla Prieto, J. Cernicharo, G. Quintana-Lacaci, M. Agúndez, A. Castro-Carrizo, J. P. Fonfría, N. Marcelino, J. Zúñiga, A. Requena, and A. Bastida
Si-bearing Molecules Toward IRC+10216: ALMA Unveils the Molecular Envelope of CW Leo
Astrophys. J. 805, Art. No. L13 (2015).
In the case of the main isotopic species of SiS, transitions up to v = 7, possibly higher, were detected. In addition, emission lines of vibrationally excited minor isotopic species were reported.
Rovibrational transitions were observed by
R. J. Boyle, J. J. Keady, D. E. Jennings, K. L. Hirsch, and G. R. Wiedemann,
Observations of 13.5 micron Rotation-Vibration Lines of SiS in IRC +10216
Astrophys. J. 420, 863868 (1994).