Monitoring of the H2O maser W31(2) in 1981–2003

Abstract

A catalog of water-vapor maser spectra at 1.35 cm for the sourceW31(2), which is associated with an active star-forming region, is presented. The observations were carried out in 1981–2003 on the 22-m antenna of the Pushchino Radio Astronomy Observatory with a spectral resolution of 0.101 km/s. The mean interval between observations was about 1.5 months. The total velocity range in which emission was observed during the monitoring is from −14 to +14 km/s. The spectrum is strongly variable and contains a large number of emission features. Two strong flares with an interval between their emission maxima (integrated flux) of about 12 years (1985–1986 and 1998–1999) were observed, as well as fast variations on a timescale of 0.5–2 years with amplitudes of up to 600 Jy km/s. No long-period component of the variations was found. A drift of the velocity centroid has been detected; it is well approximated by a third-power polynomial corresponding to a period of about 31–33 years. The two strong flares fall on different phases of this curve: the first (1985–1986) is located near the minimum, while the second (1998–1999) is at the maximum. The observed character of the variability of the emission is well explained by the existing model for the region of G10.6-0.4. The drift of the velocity centroid is probably associated with the nonstationary accretion of material onto an HII region formed by a cluster of OB stars.