A study of the kinematics of the H₂O maser sources S269 and W75S from long-term monitoring

¹ Instituto Nacional de Astrofísica, Óptica y Electrónica, Luis Enrique Erro No. 1, Apdo Postal 51 y 216, 72840 Tonantzintla, Puebla, México
² Main Astronomical Observatory of the Russian Academy of Sciences, Pulkovo, St. Petersburg, 196140, Russia
³ Sternberg Astronomical Institute, 13 Universitetskij prospekt, Moscow, 119899, Russia
⁴ Pushchino Radio Astronomy Observatory, Astrospace Center of the Lebedev Institute of Physics, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia

Corresponding author: E. E. Lekht, lekht@inaoep.mx

Received: 15 March 2001
Accepted: 21 June 2001

Abstract

It is shown that basic characteristics of turbulence can be derived from temporal behaviour, shape and radial-velocity drift of a spectral line. To perform this analysis, a 20-year monitoring of the H₂O maser emission sources S269 and W75S was used. It is shown that the observed sinusoidal variation of the radial velocity of the main emission feature in S269 with a period of 26 years is not caused by Keplerian motion. Most likely, it results from rotation of a non-uniform turbulent vortex with a diameter of about 1 AU. Within the framework of this model, asymmetry of the emission feature at 20.1 km s^-1 and a jump of the linewidth, which took place after a strong flare in 1991, are explained. In W75S anticorrelation between fluxes of several emission features with close radial velocities is found. This anticorrelation is explained by competition of spatial modes of the emission for pumping in a partially saturated maser. It is shown that in the model of a maser in an expanding envelope (which is, most likely, the case in W75S) the emission features with anticorrelated fluxes form a spatially compact group.