Time variation of the water maser in ON2

¹ Instituto Nacional de Astrofísica, Óptica y Electrónica, Luis Enrique Erro No. 1, Apdo Postal 51 y 216, 72840 Tonantzintla, Puebla, México e-mail: lekht@inaoep.mx
² Sternberg Astronomical Institute, 13 Universitetskij prospekt, Moscow, 119992, Russia e-mail: lekht@sai.msu.ru
³ Departamento de Astronomia, Universidad de Guanajuato, México
⁴ Pushchino Radio Astronomy Observatory, Astrospace Center of the Lebedev Institute of Physics, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia e-mail: tolm@prao.psn.ru

Received: 23 May 2005
Accepted: 26 April 2006

Abstract

Context.The results of monitoring of the water-vapour maser in the 1.35-cm line toward ON2 in 1995–2004 are reported.

Aims.The main goal was to study variations of the H₂O maser emission on a long (10 years) time interval, in particular, velocity drifts and correlation between fluxes in various spectral features.

Methods.The observations were carried out on the RT-22 radio telescope of Pushchino Radio Astronomy Observatory.

Results.The emission of the northern component (ON2 N) took place in a broad interval of radial velocities, from -12 to 9 km s^-1. The total H₂O emission has two variability components: slow and flaring. The period of the former component is most likely between 25 and 30 years. The flaring component has a cyclic character with a period from 1.1 to 2.6 years. The alternation of the activity cycles was accompanied by changes in the velocity structure of the H₂O spectra. There is good correlation between the variations in the integrated flux and velocity centroid, as well as between the emissions in various segments of the H₂O spectrum. We suggest that long-term variations and oscillations of the water-maser emission can be related to the non-stationarity and anisotropy of bipolar molecular outflow from the B-type star in the ultracompact H II region.