IR Observations of a Flaring Maser Source - Revealing the Unsteady Growth of Massive Stars
Event date
Bringfried Stecklum
Thueringer Landessternwarte - TLS
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In recent years, the first accretion bursts from massive YSOs have been detected. This confirmed that episodic accretion, possibly driven by disk instabilities, is a feature of high-mass star formation as well. These bursts were accompanied by flares of Class II methanol masers. Thus, maser monitoring will improve prospects to discover MYSO bursts which are hard to find otherwise. This is the objective of the Maser Monitoring Organization (M2O), founded in 2017. The first M2O alert candidate, G358.93−0.03, spotted in early 2019, lacked clear excess emission at NIR/MIR and (sub)mm wavelengths. Thus, SOFIA FIFI-LS observations were requested to verify the burst by detecting its FIR emission. The SOFIA data clearly proved the presence of an accretion burst. From two epochs, and by incorporating ALMA data, major burst properties could be derived by radiative-transfer modeling (RTM) of the pre-burst, bust, and post-burst SEDs. The analysis also revealed that accretion bursts cause thermal afterglows of dust continuum emission which fade away with a wavelength-dependent time-scale. The use of time-dependent RTM opens up the possibility to better understand the physical and chemical processes induced by the bursts in the protostellar environment. This holds particularly for the dust-maser symbiosis.

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