Variability monitoring of the hydroxyl maser emission in G12.889+0.489

Through a series of observations with the Australia Telescope Compact Array we have monitored the variability of the ground-state hydroxyl maser emission from G12.889+0.489 in all four Stokes polarization products. These observations were motivated by the known periodicity in the associated 6.7-GHz methanol maser emission. A total of 27 epochs of observations were made over 16 months. No emission was seen from either the 1612- or 1720-MHz satellite line transitions (to a typical five sigma upper limit of 0.2 Jy). The peak flux densities of the 1665- and 1667-MHz emission were observed to vary at a level of ∼20per cent (with the exception of one epoch which dropped by ≤40per cent). There was no distinct flaring activity at any epoch, but there was a weak indication of periodic variability, with a period and phase of minimum emission similar to that of methanol. There is no significant variation in the polarized properties of the hydroxyl, with Stokes Q and U flux densities varying in accord with the Stokes I intensity (linear polarization, P, varying by ≤20per cent) and the right and left circularly polarized components varying by ≤33per cent at 1665 MHz and ≤38per cent at 1667 MHz. These observations are the first monitoring observations of the hydroxyl maser emission from G12.889+0.489.