DOI

https://doi.org/10.48717/9hy9-0r33

Project

RB007

Title

e-EVN: RB007

Abstract

The theory of massive star formation is approaching resolution of some of its major hurdles. An episodic disk- mediated accretion mechanism is now emerging as the most likely process by which massive stars acheive their final masses. However observational evidence is scarce since the proposed ‘bursts’ phases of accretion are expected to comprise less than 2 percent of the star’s formative years. Only three burst events have been identified to date in massive stars: S255IR, NGC6334I and G358. G24.33+0.14 has been identified as the fourth candidate in this class by maser monitoring campaigns (via the Maser Monitoring Organisation) and is now under intense observational scrutiny to at various frequencies and facilities from radio to infrared. Low opacity and high angular resolution grants radio VLBI a clear advantage in efforts to understand the inner workings of these deeply embedded, minute regions. Maser activity in G24 has been continuously monitored by the M2O and preliminary results from a 5cm ToO conducted recently indicated changes in the methanol maser distribution. Now a flare has been identified in the 1667 MHz hydroxyl maser line, which is also a radiatively pumped maser transition and is thus expected to react to changes in the radiation field produced by an accretion burst. The 18 cm OH masers trace different physical conditions to 5 cm methanol masers and thus could present a novel tool in investigating accretion bursts. However, to date there have been no OH maser imaging observations conducted during an accretion burst in a high-mass protostar. In order to establish the use(s) of OH maser imaging studies in the investigation of high mass star accretion bursts we propose EVN+MERLIN observations to compare with earlier observations, in addition to making use of the more well established role of the paramagnetic OH molecule; as a probe of the magnetic field.