Lifetime of OH masers at the tip of the asymptotic giant branch

TL;DR

This study estimates the minimum lifetime of 1612 MHz OH masers in AGB stars to be around 2800 years, suggesting stable maser conditions over this period and providing insights into mass-loss processes.

Contribution

The paper provides the first direct measurement of OH maser lifetime in AGB stars through reobservation after 28 years, indicating a minimum of 2800 years.

Findings

All 114 OH masers were re-detected after 28 years.

Minimum maser lifetime is approximately 2800 years.

Maser velocities and flux densities remained stable over time.

Abstract

Context: A large fraction of otherwise similar asymptotic giant branch stars (AGB) do not show OH maser emission. As shown recently, a restricted lifetime may give a natural explanation as to why only part of any sample emits maser emission at a given epoch. Aims: We wish to probe the lifetime of 1612 MHz OH masers in circumstellar shells of AGB stars. Methods: We reobserved a sample of OH/IR stars discovered more than 28 years ago to determine the number of stars that may have since lost their masers. Results: We redetected all 114 OH masers. The minimum lifetime inferred is 2800 years (1 sigma). This maser lifetime applies to AGB stars with strong mass loss leading to very red infrared colors. The velocities and mean flux density levels have not changed since their discovery. As the minimum lifetime is of the same order as the wind crossing time, strong variations in the mass-loss process affecting the excitation conditions on timescales of ~3000 years or less are unlikely. Keywords: OH masers -- Stars: AGB and post-AGB -- circumstellar matter