CH₃OH Thermal Lines Traces 6.7 GHz CH₃OH Maser Variation of High-mass Protostar G353.273+0.641

Abstract This study reports an analysis of the 6.7 GHz CH 3 OH maser in the high-mass protostar G353.273+0.641 (G353), utilizing data from the Tianma Radio Telescope. G353 is a possibly periodic variation in the flux density of the maser with a period of ∼330 days. Our analysis of Atacama Large Millimeter/submillimeter Array archival data identified 44 CH 3 OH transitions within the gas envelope surrounding the protostar. The CH 3 OH envelope exhibited non–local thermodynamic equilibrium (LTE) conditions during the increase phase of the flux density of the maser, then transitioning to LTE ( T ∼ 380 K) during the decay phase of the maser. This phenomenon is likely attributed to the recurrent heating of the protostellar envelope through heat waves, which are generated by the periodic luminosity oscillations of the central high-mass protostar. The propagation velocity of the heat wave is gauged to be ∼0.02 c . These results emphasize the significance of integrating the variations in 6.7 GHz CH 3 OH masers with their surrounding circumstellar environments to advance our comprehension of high-mass star formation mechanisms.