Model of the vibrationally excited H$_2$O maser at 658 GHz in circumstellar envelopes around asymptotic giant branch stars

TL;DR

This paper models the 658 GHz vibrationally excited H$_2$O maser in circumstellar envelopes of AGB stars, predicting gain values and conditions for maser operation based on detailed molecular and environmental parameters.

Contribution

It introduces a comprehensive model of the vibrationally excited H$_2$O maser at 658 GHz, including multiple vibrational states and environmental conditions, advancing understanding of maser mechanisms in stellar envelopes.

Findings

Predicted maser gain values of 10^{-14} - 10^{-13} cm^{-1}.

Identified gas temperatures of 1000-1500 K as optimal for maser activity.

Provided results for other vibrational state maser transitions.

Abstract

The model is presented of H$_2$O maser in the $1_{10}-1_{01}$ 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 H$_2$O molecule. The model predicts the gain values of the 658-GHz maser about $10^{-14} -10^{-13}$ cm$^{-1}$ at H$_2$ molecule concentrations $10^9 - 10^{11}$ cm$^{-3}$ and at high ortho-H$_2$O concentrations $ \gtrsim 10^5$ 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.