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| EPoS Contribution |
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Periodic masers associated with high mass star forming regions
Johan van der Walt NWU, Potchefstroom, SA | |
| The phenomenon of the periodic flaring of class II methanol masers associated with a number of high mass star forming regions is now a well established fact and is the only known periodic phenomenon associated with high mass star forming regions. At present nine such star forming regions are known. It is not yet clear for all nine sources to what extent the observed periodic behaviour can be ascribed to changes in the pumping of the masers or to changes in the background seed photon flux although in the case of one source, G37.55+0.20, there now seems to be strong evidence that the flaring cannot be due to changes in the pumping. For three other sources (G9.62+0.20E, G188.89+0.95, G22.357+0.066) it has been noted that the flare profiles, in particular the decay part, resembles of what can be expected for the change of the free-free emission from a thermal plasma recombining from a higher state of ionization to a lower equilibrium state of ionization. It has been proposed that a colliding-wind binary system may be responsible for a pulse of ionizing radiation during periastron passage that changes in the level of ionization at the ionization front of the HII region against which the masers are projected. Although there is only a small number of high mass star forming regions which shows periodic methanol maser emission, the masers and in particular the periodic masers reveals the presence of physical processes and events which most likely would not have been detected by other observations. In this talk I will review the current state of research on the periodic masers and argue that for at least four sources the observed flaring of the masers is probably due to changes in the background seed photon flux. | |
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Key publication
Suggested Sessions: Massive Star Formation and Feedback | |