Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...310..259b&link_type=abstract
Astronomy and Astrophysics, v.310, p.259-270
Astronomy and Astrophysics
Astrophysics
24
Stars: U Equ, Agb, Post-Agb, Circumstellar Matter, Mass Loss, Molecular Processes, Radio Lines: Stars, Infrared: Stars
Scientific paper
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 H_2_O and OH maser observations with profiles in the literature taken in 1987 (H_2_O) 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 H_2_O and OH masers, and J and K band images and photometry.
Barnbaum Cecilia
Morris Marita
Omont Alain
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