Observations of a compact H II region and water vapor maser sources in the vicinity of the Herbig-Haro objects 7-11

Abstract

The H2O maser source near the Herbig-Haro objects H-H 7-11, which has velocity components between -10 and -30 km/s, was monitored at approximately monthly intervals over a period of three years. Two additional sites of maser emission were discovered at velocities close to the ambient cloud velocity of 8.3 km/s but separated from the original maser source by 0.5 and 2.5 arcmin, respectively. The time variations both in velocity and intensity of all three sources are characterized by periods of rapid activity lasting about 1 year, followed by a period of months to years in which the maser is unobservable within our sensitivity limits. Two of the maser sources abruptly turned on within 10 days of each other after an 18 month period of quiescence. These masers may have a common maser pump. A compact H II region coincident in angle with one of the masers was discovered. A VLBI measurement showed that the maser had an unusually small apparent size of about 3 x 10 to the 12th cm.