M2P2 I: Maser Monitoring Parkes Program data description and Stokes-I OH maser variability

The Maser Monitoring Parkes Project (M2P2) is an ongoing project to observe masers towards high mass star forming regions (HMSFRs) using the 64m CSIRO Parkes radio telescope, Murriyang. In this paper we outline the project and introduce Stokes-I data from the first two years of observations. For the 63 sightlines observed in this project we identify a total of 1514 individual maser features: 14.4% of these (203) towards 27 sightlines show significant variability. Most of these (160/203) are seen in the main-line transitions of OH at 1665 and 1667 MHz, but this data set also includes a significant number of variable features in the satellite lines at 1612 and 1720MHz (33 and 10 respectively), most of which (24 and 9 respectively) appear to be associated with the HMSFRs. We divide these features into 4 broad categories based on the behaviour of their intensity over time: flares (6%), periodic (11%), long-term trends (33%) and ‘other’ (50%). Variable masers provide a unique laboratory for the modelling of local environmental conditions of HMSFRs, and follow-up publications will delve into this in more detail.