Variable hydroxyl and methanol masers in G 351.78-0.54

Abstract

The results of monitoring the 1.6-GHz hydroxyl and 6.7-GHz methanol masers in the star-forming region G 351.78 -0.54 from 1993 to mid-1995 are reported. Variations with time-scales of a few months are superimposed on long-term changes with a time-scale of years in the brightest 1.665- and 1.667-GHz maser peaks and in both 6.7-GHz maser peaks. The methanol maser feature at + 1.2 km s-1 flared at least seven times, varying in brightness from 50 to 300 Jy. Each flare began at the redshifted end of the feature, taking between 10 and 35 d to progress to the blueshifted end. The methanol maser feature at + 1.7 km s-1 experienced smaller changes, the peak flux varying between 150 and 210 Jy. No phase lag was seen across this peak or the 1,665-GHz hydroxyl maser peak at -1.8 km s-1 during variations.