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Nebulae around evolved massive stars


Olga Maryeva
Astronomical Institute of Czech Academy of Sciences

December 13th, 2018


Abstract

Massive stars (with masses higher than 30 M) undergo the mass loss during their whole lifes. During hydrogen burning in their cores massive stars demonstrate fast winds with velocity about V∞=2500 km/s and relatively low mass-loss rate about 10 -7-10-6 M/year. At the same time, after the end of core hydrogen burning stars become less stable and mass-loss rate increases, stars move to the stage of Luminous Blue variable (LBV). LBVs are relatively short evolutionary stage in life of massive stars, during which they lose significant amount of mass through strong stellar winds and occasional giant eruptive events. As a result, they shed their outer layers and eventually become hydrogen-deficient Wolf–Rayet stars. Massive stars with 25-40 Mreach LBV stage after being red supergiants i.e. reaching cool end on Hertzsprung– Russell diagram, more massive stars became LBV right after blue supergiants phase. Consideration of the initial mass function leads to conclusion that LBV stars are extremely rare and there should be no more than a few dozens such objects in the Galaxy. Detection of LBV- like shells may be considered an indication of that their associated stars are massive and evolved. Searches for such shells using the infrared surveys resulted in the discovery of many dozens of such shells, while follow-up spectroscopy of their central stars led to the discovery of dozens of new candidates to LBVs. In the talk I will tell about properties of nebula around post-LBV star GR290 and about estimated parameters of couple of stars with LBV-like shells, and discuss that at least in some cases the envelope loss occurs before LBV stage.

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