Model of the vibrationally excited H2O maser at 658 GHz in circumstellar envelopes around asymptotic giant branch stars
Abstract
The model is presented of H2O maser in the 110-101 line within the first excited vibrational state of the molecule around oxygen-rich asymptotic giant branch stars. It is suggested that the maser cloud is located in the inner layers of the circumstellar envelope where intense dust formation takes place. The calculations took into account rotational levels belonging to the five lowest vibrational states of the H2O molecule. The model predicts the gain values of the 658-GHz maser about 10-14 -10-13 cm-1 at H2 molecule concentrations 109 - 1011 cm-3 and at high ortho-H2O concentrations 105 cm-3. The gas temperatures 1000 - 1500 K are considered to be a necessary condition for the effective maser operation. Results are presented for other maser transitions of the excited vibrational states of the molecule.