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(Nov. 14) Stellar Astronomy with eDAMS

Last updated :2018-11-08

Topic: Stellar Astronomy with eDAMS
Speaker: Jun-ichi Nakashima
(Ural Federal University)
Invited by: ZHANG Yong
Time: 15:00-16:00, Wednesday, November 14, 2018
Venue: Room 107, Red House 17, Zhuhai Campus, SYSU

Molecular maser lines emitted from circumstellar envelopes of evolved stars are known as a useful probe not only of the kinematic of the envelope, but also of some other physical conditions, such as the temperature and density of maser emitting regions. Our research group in the Ural Federal University is currently developing a large-scale on-line database of circumstellar maser sources (i.e., eDAMS: extended Database of Astrophysical Maser Sources). The main motivation of the eDAMS project is to collect the data of maser sources as well as constructing/providing on-line tools, which enable us to easily execute various kinds of analyses. In this talk, some of the pilot studies, which show future scientific possibilities using eDAMS, are introduced, as well as introducing the eDAMS project.

Although eDAMS is for general purposes and many applications are possible, one of our original motivation for constructing eDAMS is to provide a convenient tool used for cross-checking between maser sources and various astronomical catalogs. As a pilot study of a future application of eDAMS, our research group has systematically compared the line profile of the 1612 MHz OH maser line with that of the 22 GHz H2O maser line for the samples of cold infrared sources, and we found that astrophysically curious objects could be selected by a very simple criterion. These two maser lines are often emitted from late-type stars exhibiting active mass-loss. Such the mass-losing evolved stars lying at the asymptotic giant branch (AGB) phase or the red supergiant (RSG) phase are usually surrounded by a spherically expanding envelope of molecules and dusts. In such a spherically symmetric case, it is known that the velocity range of 22 GHz H2O maser emission (VH2O) is smaller than that of 1612 MHz OH maser emission (VOH): i.e., VOH > VH2O.

On the contrary, we found that several percent of objects in the sample exhibit the relation opposite to the typical case: i.e., VOH < VH2O. Our follow-up studies show that such the opposite cases include two kinds of curious objects, which are the candidates for water fountains and red nova remnants. Depending on the future development of research, there is a possibility that these two kinds of objects have a significant meaning in the stellar evolution of stars particularly in its late stage, physical processes of stellar merger, and circumstellar/interstellar chemistry.
Speaker's CV: 
Name: Jun-ichi Nakashima
Academic qualifications: Ph.D. (Graduate University for Advanced Studies, 2002), M.Sc. (Osaka Kyoiku University, 1999), B.Sc. (Okayama University of Science, 1995)
Present position: Professor, Dept. of Astronomy and Geodesy, Ural Federal University (02/2015–present)
Research Field: My research field includes evolved star mass-loss, astrophysical masers, and radio/infrared observations. Recently, I am leading the eDAMS project (http://maserdb.net/), which is constructing a large-scale on-line database system of circumstellar maser sources.