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arXiv · 1506.06551

Methanol Observation of IRAS 19312+1950: A Possible New Type of Class I Methanol Masers

Jun-ichi Nakashima·Andrej M. Sobolev·Svetlana V. Salii·Yong Zhang·Bosco H. K. Yung·Shuji Deguchi
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Abstract

We report the result of a systematic methanol observation toward IRAS 19312+1950. The properties of the SiO, H2O and OH masers of this object are consistent with those of mass-losing evolved stars, but some other properties are difficult to explain in the standard scheme of stellar evolution in its late stage. Interestingly, a tentative detection of radio methanol lines was suggested toward this object by a previous observation. To date, there are no confirmed detections of methanol emission towards evolved stars, so investigation of this possible detection is important to better understand the circumstellar physical/chemical environment of IRAS 19312+1950. In this study, we systematically observed multiple methanol lines of IRAS 19312+1950 in the lambda=3mm, 7mm, and 13mm bands, and detected 6 lines including 4 thermal lines and 2 class I maser lines. We derived basic physical parameters including kinetic temperature and relative abundances by fitting a radiative transfer model. According to the derived excitation temperature and line profiles, a spherically expanding outflow lying at the center of the nebulosity is excluded from the possibilities for methanol emission regions. The detection of class I methanol maser emission suggests that a shock region is involved in the system of IRAS 19312+1950. If the central star of IRAS 19312+1950 is an evolved star as suggested in the past, the class I maser detected in the present observation is the first case detected in an interaction region between an evolved star outflow and ambient molecular gas.

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Jun-ichi Nakashima, Andrej M. Sobolev, Svetlana V. Salii, Yong Zhang, Bosco H. K. Yung, Shuji Deguchi. 2015-06-22. Methanol Observation of IRAS 19312+1950: A Possible New Type of Class I Methanol Masers. https://doi.org/10.1093/pasj%2Fpsv064

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