Variability of methanol and OH masers in G339.62−0.12

Abstract

ABSTRACT The study of the periodic variability of masers has greatly increased after the discovery of periodic class II methanol (CH3OH) masers. Currently, more than 20 masers associated with various high-mass star-forming regions have shown this interesting behaviour. Since the mainline OH masers are pumped under similar conditions as that of the class II methanol masers, it becomes necessary to also search for periodic behaviour of OH masers. In this paper, we present the results of the 6.7 GHz methanol and mainline OH masers associated with G339.62−0.12 observed using the 26 m HartRAO single-dish and the KAT-7 telescopes, respectively. We find evidence of variability, however, periodic variability is clearly visible for the masers that are blue-shifted from the systemic velocity ($\mathrm{\mathit{ \mathit{V}}_{lsr} = -34.2~km\, s^{-1}}$ ). Using the Lomb–Scargle periodogram, the blue-shifted methanol masers have periods of 208 ± 4 d while the blue-shifted OH 1665 and 1667 MHz masers have average periods of 208 d. Further analysis suggests that the maser profiles are similar, having a delay of 5 d (∼870 au) between the 6.7 GHz methanol maser and the 1667 MHz OH maser, as well as a delay of 15 d (∼2600 au) between the 6.7 GHz methanol maser and the 1665 MHz OH maser. To further interpret the observed periodic behaviour as well as the similarities found in the profiles of these masers will require high-resolution observations of the OH and methanol masers and high-resolution mm/sub-mm observations of the G339.62−0.12 source.