Methanol Masers—Are They in Circumstellar Disks?

Abstract

Since the discovery of the 12.2 and 6.7 GHz methanol maser lines, these masers have been studied in great detail. Even in the earliest studies, it appeared that in some fraction of the sources, the maser spots were arranged in lines. This contrasts with the well-studied OH and water masers, in which the masers tended to be clustered almost randomly around a compact H ɪɪ region. Here I describe recent work to investigate the hypothesis that these lines represent edge-on circumstellar disks.

EVN imaging of methanol masers towards massive protostars

“…VLBI observations with milliarcsecond (mas) scale reveal various morphologies of methanol maser sources from simple to complex structures ( [4], [7], [9], [10], [14]). Their origin has not been established yet.…”

Methanol masers survey using EVN

“…We suppose that superb sensitivity of EVN enabled us to detect such structures, in relatively weaker targets (S p =≤ 28.3 Jy). A typical peak flux density in the cross-correlated spectra is 3.6 Jy beam −1 , while in the previous surveys it was 10-100 times higher ( [8]; [9]; [6]; [13]; [4]).…”

“…VLBI observations with milliarcsecond (mas) scale have been carried out for many years to date. The structures of the maser emission are from simple to complex structures indicating they may form in outflows or behind shocks driven by a protostar or in discs/torii around a central object ( [4], [6], [8], [9], [13]). Their origin has not been established yet.…”