Variability of the OH and H2O maser emission toward AS 501

Abstract

The results of observations of OH (λ = 18 cm) and H2O (λ = 1.35 cm) masers toward AS 501 obtained with the Nancay Observatory Radio Telescope (France) and the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia), respectively, are presented. Nine cycles of H2O maser activity ranging from 2.8 to 6.0 years were detected, identifying AS 501 as an irregular variable star. Zeeman splitting was found only in the 1612-MHz satellite line at −59.2 km/s. The splitting is 0.11 km/s, corresponding to a line-of-sight magnetic field strength of 0.48 mG. The field is directed toward the observer. The detected radial-velocity drift of the H2O emission features can be explained in a model with elongated filaments with radial-velocity gradients.