Relative astrometry of the J=1-0, v=1 and v=2 SiO masers towards R Leonis Minoris using VERA

TL;DR

This study used VERA to produce relative astrometrically aligned SiO maser maps of R Leonis Minoris, revealing insights into the circumstellar environment and challenging existing theoretical models of maser emission.

Contribution

First-time relative astrometric alignment of v=1 and v=2 SiO masers at multiple epochs around RLMi using VERA, overcoming calibration challenges.

Findings

Aligned SiO maser maps at multiple epochs show spatial relationships.

Results challenge current maser pumping mechanism models.

Method developed for accurate coordinate relation despite weak calibrator signals.

Abstract

Oxygen-rich Asymptotic Giant Branch (AGB) stars are intense emitters of SiO and H$_2$O maser lines at 43 (J=1-0, v=1 and 2) and 22 GHz, respectively. VLBI observations of the maser emission provides a unique tool to sample the innermost layers of the circumstellar envelopes in AGB stars. Nevertheless, the difficulties in achieving astrometrically aligned v=1 and v=2 SiO maser maps have traditionally prevented a unique interpretation of the observations in terms of physical underlying conditions, which depend on the nature of the SiO pumping mechanism. We have carried out observations of the SiO and H$_2$O maser emission towards RLMi, using the astrometric capabilities of VERA. Due to the too-weak emission of the reference calibrator we had to develop a special method to accurately relate the coordinates for both transitions. We present relative astrometrically aligned v=1 and v=2 J=1-0 SiO maser maps, at multiple epochs, and discuss the astrophysical results. The incorporation of astrometric information into the maps of SiO masers challenges the weak points in the current theoretical models, which will need further refinements to address the observations results.