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Astrophysical masers: see definition in Wikipedia

Different types of astrophysical masers:

Radio wave masers

(Sub)mm masers SiS masers Henkel et al., (1983ApJ...267..184H) detected SiS maser emission in J=1-0 transition in IRC +10216. SiS masers: Fonfría Expósito et al., (2006ApJ...646L.127F) reported detection of SiS mm masers in their J=11-10, J=14-13, and J=15-14 transitions of the v=0 vibrational state in IRC +10216. The maser pumping mechanism could be line overlap with  mid-IR lines of C2H2, HCN, and their 13C isotopologues. HCN masers Izumiura et al., (1995ApJ...440..728I) detected HCN v=0, J=1-0 maser lines from 5 optical carbon stars.  Lucas and Cernicharo, (1989A&A...218L..20L) detected HCN J=2-1 (011c0) masers in IRC +10216. Schilke et al., (2000ApJ...528L..37S) reported the HCN J=9-8 (0400) maser at 805 GHz in IRC +10216. Chemical pumping is suggested for this maser in the inner hot part of circumstellar envelope. Bieging, (2001ApJ...549L.125B) detected HCN J=3-2, 4-3 (011c0) maser towards five carbon stars: R Scl, V384 Per, R Lep, Y CVn, and V Cyg. He used the ARO HHT 10M telescope. Schilke and Menten, (2003ApJ...583..446S) detected HCN J=10-9 maser (891 GHz) in the hot excited vibrational states (1110) and (0400). The levels are higher than 4200K, and so the maser should comes from inner part of the circumstellar envelope and may probe the dust formation region.  CS masers Highberger et al., (2000ApJ...544..881H) reported CS v=1, J=3-2, 6-5, 7-6 maser emission from IRC +10216, using NRAO 12m telescope. The velocity of the maser line suggests they arise in the inner part of the circumstellar envelope. H2O maser CH3OH maser Class-I methanol maser: 6.7 GHz masers offset from IR sources and other transitions than the 6.7 GHz one. Class-II methanol maser: 6.7 GHz masers tightly associated with IR sources, OH masers, and H II regions. With new collision data, type II CH3OH masers are still pumped by IR radiation. A gas temperature above 100K can well reproduce the observed CH3OH masers in W3(OH). An updated list of methanol II maser candidates is given. (from Cragg et al., 2005MNRAS.360..533C)