Phase-lag Distances of OH Masing AGB Stars

TL;DR

This paper discusses a method to determine distances to OH maser-emitting AGB stars using phase-lag measurements combined with interferometry, providing a way to measure distances where optical parallaxes are ineffective.

Contribution

It introduces the phase-lag method for distance measurement of OH/IR stars and reports phase-lag measurements for 20 galactic disk stars based on long-term radio observations.

Findings

Phase-lag measurements obtained for 20 stars.

Estimated distance uncertainties are around 20%.

Ongoing interferometric observations will refine measurements.

Abstract

Distances to AGB stars with optically thick circumstellar shells cannot be determined using optical parallaxes. However, for stars with OH 1612 MHz maser emission emanating from their circumstellar shells, distances can be determined by the phase-lag method. This method combines a linear diameter obtained from a phase-lag measurement with an angular diameter obtained from interferometry. The phase-lag of the variable emission from the back and front sides of the shells has been determined for 20 OH/IR stars in the galactic disk. These measurements are based on a monitoring program with the Nancay radio telescope ongoing for more than 6 years. The interferometric observations are continuing. We estimate that the uncertainties of the distance determination will be ~20%.