Silicon monoxide, SiO, is very widespread in space. It is generally viewed as an indicator of shocks. It was among the first molecules detected in space by means of radio astronomy.
R. W. Wilson, A. A. Penzias, K. B. Jefferts, M. Kutner, and P. Thaddeus
reported on the
Discovery of Interstellar Silicon Monoxide
Astrophys. J. 167, L97–L100 (1971).
The J = 3 – 2 transition of SiO near 130.2 GHz was detected in emission with the 11 m Kitt Peak telescope toward Sgr B2(OH).
D. F. Dickinson
reported on the
Detection of Silicon Monoxide at 87 GHz
Astrophys. J. 175, L43–L100 (1972).
The 11 m Kitt Peak telescope was used to detect the line toward Sgr B2(OH) and Orion A.

P. Schilke, G. Pineau des Forêts, C. M. Walmsley, and J. Martín-Pintado
Observations of SiO towards Photon Dominated Regions
Astron. Astrophys. 372, 291–301 (2001).
The IRAM 30 m telecope was used to detect several SiO transitions toward the Orion Bar and S 140.

S. Yamamoto, H. Mikami, S. Saito, N. Kaifu, M. Ohishi, and K. Kawaguchi
SiO in Barnard 1
Publs. Astron. Soc. Japan 167, L97–L100 (1971),
a low-mass star-forming region.

The molecule is conspicuously absent in cold, quiescent molecular clouds, as reported by
L. M. Ziurys, P. Friberg, and W. M. Irvine,
Interstellar SiO as a Tracer of High-temperature Chemistry
Astrophys. J. 343, 201–207 (1989).
The absence of SiO was reported for TMC-1, L134N (aka L183) and for B335 (aka L663). Hence,
J. Martin-Pintado, R. Bachiller, and A. Fuente
SiO Emission as a Tracer of Shocked Gas in Molecular Outflows
Astron. Astrophys. 254, 315–326 (1992).

L. E. Snyder and D. Buhl
proposed the
Detection of Possible Maser Emission Near 3.48 Millimeters from an Unidentified Molecular Species in Orion
Astrophys. J. 189, L31–L33 (1974).
Orion A was observed with the 11 m Kitt Peak telescope. The frequency coincidence with the J = 2 – 1 transition of SiO in its first excited vibrational state was noted.
Confirmation came from
J. H. Davis, G. N. Blair, H. van Till, and P. Thaddeus,
who studied
Vibrationally Excited Silicon Monoxide in the Orion Nebula
Astrophys. J. 190, L117–L119 (1974).
They observed the J = 3 – 2 transition of SiO.

D. Buhl, L. E. Snyder, F. J. Lovas, and D. R. Johnson
reported subsequently on
Silicon Monoxide: Detection of Maser Emission from the Second Vibrationally Excited State
Astrophys. J. 192, L97–L100 (1974).
Half of the authors are laboratory spectroscopists, thus highlighting the crucial importance for radio astronomical observations.

T. Kaminski, C. A. Gottlieb, K. H. Young, K. M. Menten, and N. A. Patel
An Interferometric Spectral Line and Imaging Survey of VY Canis Majoris in the 345 GHz Band
Astrophys. J. Suppl. Ser. 209, Art. No. 38 (2013),
and detected a v = 5 SiO maser.

E. Gonzalez-Alfonso, J. Alcolea, and J. Cernicharo
reported on the
Detection of <sup>29</sup>SiO //v// = 3 //J// = 8 → 7 Maser Emission: a new IR SiO Overlap
Astron. Astrophys. 313, L13–L16 (1996).

S.-H. Cho, H.-G. Kim, Y.-S. Park, C.-H. Choi, and N. Ukita
reported on the
First Detection of <sup>28</sup>Si<sup>18</sup>O Maser and Thermal Emission from Orion KL
Astrophys. J. 622, 390–392 (2005).

L. Decin, J. Cernicharo, M. J. Barlow, et al.
Silicon in the Dust Formation Zone of IRC +10216
Astron. Astrophys. 518, Art. No. L143 (2010).
Using the PACS low-resolution spectrometer on board of the Herschel satellite, they identified unblended SiO rotational transitions beyond 3 THz.

The observation of 28Si17O was reported by
L. Velilla Prieto, C. Sánchez Contreras, J. Cernicharo, M. Agúndez, G. Quintana-Lacaci, V. Bujarrabal, J. Alcolea, C. Balança, F. Herpin, K. M. Menten, and F. Wyrowski
in the course of
The Millimeter IRAM-30m Line Survey toward IK Tauri
Astron. Astrophys. 597, Art. No. A25 (2017).

L. Decin, A. M. S. Richards, T. Danilovich, W. Homan, and J. A. Nuth
reported on an
ALMA Spectral Line and Imaging Survey of a Low and a High Mass-loss Rate AGB Star between 335 and 362 GHz
Astron. Astrophys. 615, Art. No. A28 (2018).
The low mass-loss star was R Dor, the high mass-loss star was IK Tau. The very sensitive data permitted detection of 29Si18O and 30Si18O.

Contributor(s): H. S. P. Müller; 12, 2014; 10, 2018

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