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Properties and evolutionary state of massive stars across the HR diagram

Dr. Michalis Kourniotis
Astronomical Institute of the Czech Academy

March 28th, 2019


The advanced stages of high-mass stars are characterized by episodic mass loss shed during phases of instability. Key for assigning these stars a proper evolutionary state is to assess the composition and geometry of their ejecta alongside the stellar properties. I will speak about my work to increase the number of B[e] supergiants, Yellow Hypergiants and Luminous Blue variables in the Local Group by investigating circumstellar environments and exploring the evolutionary properties of high-luminous, dusty targets. By conducting and analyzing optical spectroscopy alongside fitting the spectral energy distribution, I derive stellar properties and infer the presence of circumstellar dust. In search of processed ejected material, modeling of the CO band heads in the K-band is further employed. Results of my work in M33 include the discovery of a strong Yellow Hypergiant candidate showing evidence of past eruption. Moreover, the insight into the surrounding molecular environment witnesses the presence of circumstellar/binary disks around post-supergiant/evolved stars. I highlight the importance of the infrared data to resolve the evolutionary status of massive stars and thus, to constrain the physics of the diverse pre-supernova stellar states. Finally, I will speak about my work at IAC regarding the photometric properties of OB stars in conjunction to the latest Gaia Data Release 2 and their possible link to the line-broadening status of the stars.