Long-term monitoring of the water-vapor maser in NGC 7538: 1981–1992 |
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| Authors: | E E Lekht V A Munitsyn A M Tolmachev |
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| Institution: | (1) Instituto Nacional de Astrofísica, óptica y Electrónica, Luis Enrique Erro No. 1, Apdo Postal 51 y 216, 72840 Tonantzintla, Puebla, México;(2) Sternberg Astronomical Institute, Universitetskii pr. 13, Moscow, 119992, Russia;(3) Space Research Institute, Russian Academy of Sciences, Profsoyuznaya ul. 84/32, Moscow, 117810, Russia;(4) Pushchino Radio Astronomy Observatory, Astro Space Center, Lebedev Physical Institute, Russian Academy of Sciences, Pushchino, Moscow oblast, 142290, Russia |
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| Abstract: | We report the results of monitoring the H2O maser in NGC 7538, which is associated with a star-forming region. The observations were carried out on the 22-meter telescope of the Pushchino Radio Astronomy Observatory. Two intervals of long-term variability of the integrated flux that reflect the cyclic activity of the maser have been distinguished (1981–1992 and 1993–2003); the data for the earlier activity cycle, 1981–1992, have been analyzed. The period of the long-time-scale variations is about 13–14 years. Flares of individual spectral features and of two groups of features with mean radial velocities of ?60 and ?46.6 km/s have been observed. The flares lasted from 0.3 to 1 year. The emission features observed during the 1984–1985 flare at radial velocities between ?62 and ?58 km/s probably form a spatially compact group of spots (<1015 cm) in NGC 7538 IRS 1. The triplet structure of the spectra can be traced. The observed anticorrelations and correlations of the fluxes of the triplet components suggest that the maser spots may be located either in a protoplanetary disk or in a high-velocity gaseous outflow. |
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