FeO had been identified previously by its electronic spectrum in stellar atmospheres.
Very recently, its lowest energy J = 5 4 transition has been
detected in the ISM towards Sgr B2 M:
C. M. Walmsley, R. Bachiller, G. Pineau des Forêts, and P. Schilke,
Detection of FeO toward Sagittarius B2
Astrophys. J. 566, L109L112 (2002).
Since this is the only transition identified positively the detection is viewed as tentative in that paper.
More recently, the spatial distribution of this transition has been investigated:
R. S. Furuya, C. M. Walmsley, K. Nakanishi, P. Schilke, and R. Bachiller,
Interferometric observations of FeO towards Sagittarius B2
Astron. Astrophys. 409, L21L24 (2003).