Koichiro Sugiyama
(Yamaguchi University)
Investigations of the high-mass star formation with the methanol-- Koichiro Sugiyama Seminar
High-mass star has important clues for making heavy elements, supplying almost of luminous sources, and compressing interstellar medium for forming next generation stars by an expansion of HII regions and supernovae. However, there are still issues in the process of the
high-mass star formation, which are especially evolutions of a circumstellar disk around a high-mass young steller object (YSO) and jet/outflow system. We have started the VLBI monitor project of the 6.7 GHz methanol masers for measurements of relative proper motions by using the East Asian VLBI Network (EAVN) since 2010 yr. The 6.7 GHz methanol maser can be the best tracer of circumsteller disks around high-mass YSOs due to its detection at early evolutionary phase in high-mass star formation and its ring/elliptical spatial morphology. Also, recently the
rotational with infall/expansion proper motions have been detected in some methanol maser sources, including the proper motions measured by the EAVN.
In this seminar, we report the VLBI images with the EAVN for 22 methanol maser sources obtained in 2010 sessions as 1st epoch. The spatial morphology in some sources showed the elliptical morphology and a major axis of the ellipse was perpendicular to a shock tracer named as the EGO (Extended Green Object). The methanol maser sources showing the elliptical morphology had gas accretion rate one order of magnitude higher than that in other sources from the SED fittings. Probably, its high accretion rate could indicate that the elliptical morphology can be observed in earlier evolutionary phase of the high-mass star formation.
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