SiO masers from AGB stars in the vibrationally excited<i>v</i>= 1,<i>v</i>= 2, and<i>v</i>= 3 states

Abstract

Context. The v = 1 and v = 2 J = 1–0 (43 GHz), and v = 1 J = 2–1 (86 GHz) SiO masers are intense in asymptotic giant branch (AGB) stars and have been mapped using very long baseline interferometry (VLBI) showing ring-like distributions. Those of the v = 1, v = 2 J = 1–0 masers are similar, but the spots are rarely coincident, while the v = 1 J = 2–1 maser arises from a well-separated region farther out. These relative locations can be explained by models tools that include the overlap of two IR lines of SiO and H2O. The v = 3 J = 1–0 line is not directly affected by any line overlap and its spot structure and position, relative to the other lines, is a good test to the standard pumping models.