APEX Band 9 Reveals Vibrationally Excited Water Sources in Evolved Stars
Résumé
We have used the Atacama Pathfinder Experiment (APEX) telescope with the sensitive Swedish-ESO PI APEX (SEPIA) Band 9 receiver to discover several new vibrationally excited line sources of water at 658 GHz in the atmosphere of selected O-rich evolved stars. We have shown that this transition is masing and can be used to probe the gas in the dust formation zone or the wind beyond the central star. The 658 GHz line is widespread in evolved stars but most sources are weaker than about 300–500 Jy. However, some exceptional cases reach up to a few thousand Jy. New models incorporating several vibrationally excited transitions of water allow us to predict the physical conditions prevailing in 658 GHz sources. The strongest ones could be mapped with ALMA to study the small-scale clumpiness of the gas in the dust formation zone or, more generally, the stellar wind.