EPoS Contribution

Episodic accretion in high-mass star formation: Follow-up on accretion-burst sources Hendrik Linz MPIA Heidelberg & FSU Jena, Heidelberg, DE
The question how high-mass protostars gain their mass is still debated. Most scenarios include a circumstellar disk as a main ingredient. Recent numerical simulations predict that sufficiently massive disks could form gravitational instabilities, which eventually can enable burst-like accretion events. Some theorists predict that a considerable fraction of the total mass of a future high-mass star is being accumulated in such events. We need to underpin such predictions with observations, but to catch such outburst events is a delicate business. The Maser Monitoring Organisation (M2O) monitors methanol Class II masers, being pumped by thermal IR radiation, as a very sensitive rapid-alert system to the release of accretion luminosity. Other colleagues from M2O will present recent work that is more closely related to the actual maser follow-up observations using high-spatial resolution radio facilities. We show examples of follow-up work from a multi-wavelength perspective of such maser outburst sources. In the case of the periodic source G107 (P~34.5 d) we could show the simultaneous variation of the maser intensity and the 3-5 micron continuum radiation recorded by Spitzer over a full period, probably one of the first measurements of its kind. Unfortunately, two workhorses for thermal-IR follow-up and SED characterisation (SOFIA and [NEO]WISE) have already been or will soon be decommissioned. But we will emphasise what quantities of the outbursting systems can be extracted based on near- and mid-infrared photometry + spectroscopy from ground and from space (e.g., with JWST, which we recently utilised to observe one system that had a intermediately strong maser flare).

Caption: Multi-epoch follow-up observations of the maser outburst source G358: blue (pre-burst), red (burst), green (burst-declined). With help of the fast-response SOFIA FIR data a significant increase in FIR brightness could be confirmed, and SED modelling points to a released burst energy of 2.9x10³⁸ J.
Collaborators: B. Stecklum, TLS Tautenburg, DE V. Wolf, TLS Tautenburg, DE R. Burns, Riken, JP A. Caratti o Garatti, INAF, IT O. Bayandina, INAF, IT A. Sobolev, UrFU, RU	Key publication Relevant topic(s): Accretion Disks High-Mass SF
Relevant Big Question: What happens during a maser outburst of high-mass protostars, and how does it relate to the burst accretion mode in these objects?