Observation of water masers and a study of their time variation

Using the 25-m telescope of Shanghai Observatory, Joint Radio Astronomy Laboratory, 19 known maser sources and 20 candidates in H II regions were surveyed for water vapour maser emission at 22.2 GHz. 21 sources were detected, of which two are for the first time. Combining with some previous data, the time variations in the flux and velocity are obtained and discussed. Time variation in the peak flux density is common and is of two types, a change in the intensity of the same peak, and a swapping-over of two peaks. The corresponding IRAS sources were identified and the relation between the maser emission and the infrared parameters discussed. It is shown that maser production rate is more sensitive to the infrared flux intensity than the infrared colour distribution.