学术报告—When massive stars spinning too fast: Be phenomena in the mid-infrared

Abstract
Massive stars are one of the important test labs on how the material behaves in extreme physical situations. As fast rotators, the material in their equator may be ejected from the star’s surface, forming a so-called decretion disk. Current models show that when a star develops a decretion disk, it would become brighter and redder in the infrared. Such behavior shed light on detecting Be stars, or moreover, the transition process between B and Be stars in IR. We found that 916 Be stars (736 newly discovered) developed/lost decretion disks in the past 13 year using the light curve from the WISE satellite. Further investigation using Gaia catalog as input shows that the number of such stars is expected to be around 3000, an order larger than those found in the previous studies. Combining the WISE and optical photometry, as well as the epoch spectroscopic observation (LAMOST, 4MOST, etc) would provide important constraints on the mechanism of decretion disk formation.

Bio
Mingjie is currently a postdoctoral researcher in the Department of Astronomy at Stockholm University. He completed his undergraduate studies at Beijing Normal University in 2016 and earned his Ph.D. from the University of Tokyo in 2022. His research interests mainly lie in Galactic archaeology and the variability of massive stars. He has studied the behavior of spectral lines in stellar atmospheres and determined elemental abundances using high-resolution spectroscopic data. He is a permanent member of the 4-meter Multi-Object Spectroscopic Telescope (4MOST) survey, responsible for developing the stellar parameter pipeline for Milky Way stars, contributing to uncovering the formation and evolutionary history of the Milky Way.