Detection of J = 5-4 SiO masers in late-type stars

Abstract

We have detected v = 1, J = 5-4 SiO maser emission from R Leo, chi Cyg, and VX Sgr and v = 2, J = 4-5 maser emission from VX Sgr. Upper limits are reported for maser emission in the J = 6-5, v = 1 and v = 2, and J = 2-1, v = 3 transitions toward several late-type stars. Maser photon emission rates for the high J transitions which have been detected are roughly comparable to emission rates for the lower J transitions. Various maser pump mechanisms and emission regions are discussed, and published numerical models are compared with the observations. No single model emerges as the best explanation of SiO maser phenomena.