Results of Long-Term Observations of the Maser Emission Source W44C (G34.3+0.15) in the OH and H2O Radio Lines

TL;DR

This study presents long-term monitoring of OH and H2O masers in W44C, revealing periodic activity, flare patterns, and magnetic field estimates, contributing to understanding star formation processes.

Contribution

It provides the first extensive multi-decade observational analysis of maser activity and magnetic fields in W44C, highlighting cyclic behavior and flare associations with protostellar activity.

Findings

Average maser activity period of ~14 years.

Identification of two flare series linked to shock fronts.

Zeeman splitting indicating a 1.2 mG magnetic field.

Abstract

Results of monitoring the H$_2$O and OH masers in W44C, located near the cometary HII region G34.3+0.15, are reported. Observations in the water-vapor line at $\lambda = 1.35$ cm were carried out on the 22-meter radio telescope of the Pushchino Radio Astronomy Observatory (Russia) from November 1979 to March 2011, and in the hydroxyl lines at $\lambda = 18$ cm on the Large Nan{\c{c}}ay radio telescope (France). Activity maxima and minima of the water maser alternated. The average period of the activity is $\sim 14$ years, consistent with results obtained earlier for a number of other sources associated with regions of active star formation. In periods of enhanced maser activity, two series of strong H$_2$O maser flares were observed, which were related to two different clusters of maser spots located at the front of a shock at the periphery of the ultracompact region UH II. These series of flares may be associated with cyclic activity of the protostellar object in UH II. In the remaining time intervals, there were mainly short-lived flares of single features. The Stokes parameters for the observations in the hydroxyl lines were determined. Zeeman splitting was observed in the profile of the 1667 MHz OH main line at a velocity of 58.5 km/s, and was used estimate the intensity of the line-of-sight component of the magnetic field (1.2 mG).