1996A&A...310..259B

In the course of a spectroscopic survey to identify cold IRAS stars, we discovered that the evolved star, U Equ, has a very peculiar optical spectrum indicating an unusual circumstellar environment. The moderate resolution (62A/mm) spectrum has deep, yet unusually thin, molecular absorption features that must arise in cold gas at a large distance from the star. The optical spectrum also has striking molecular emission lines of TiO, AlO, VO possibly due to a fluorescence mechanism. Although the IRAS 25/12µm colors of U Equ are typical of optically thin circumstellar envelopes, the LRS spectrum displays a strong 10 µm silicate absorption band, indicating a thick, dusty envelope. Comparing our H₂O and OH maser observations with profiles in the literature taken in 1987 (H₂O) and 1990 (OH), we have found a variable velocity pattern and profile shape. We suggest that the star is of a warm spectral type, G to early K, and that it has an edge-on dusty disk or torus and an inner warm molecular circumstellar shell. The luminosity criteria in our moderate-resolution spectra are consistent with that of an evolved giant. The velocity and Galactic latitude are not consistent with an early pre-main sequence evolutionary stage; however, the line-of-sight proximity of U Equ and a bright ribbon of IRAS Galactic cirrus suggest further investigation into the interstellar environment is needed. We present optical spectra, profiles of the H₂O and OH masers, and J and K band images and photometry.