Abstract
Luminous Blue Variables are massive evolved stars, here we introduce this outstanding class of objects. Described are the specific characteristics, the evolutionary state and what they are connected to other phases and types of massive stars. Our current knowledge of LBVs is limited by the fact that in comparison to other stellar classes and phases only a few “true” LBVs are known. This results from the lack of a unique, fast and always reliable identification scheme for LBVs. It literally takes time to get a true classification of a LBV. In addition the short duration of the LBV phase makes it even harder to catch and identify a star as LBV. We summarize here what is known so far, give an overview of the LBV population and the list of LBV host galaxies. LBV are clearly an important and still not fully understood phase in the live of (very) massive stars, especially due to the large and time variable mass loss during the LBV phase. We like to emphasize again the problem how to clearly identify LBV and that there are more than just one type of LBVs: The giant eruption LBVs or η Car analogs and the S Dor cycle LBVs.
Highlights
Research Department Plasmas with Complex Interactions, Ruhr University Bochum, Ruhr Astroparticle and Plasma Physics (RAPP) Center, 44801 Bochum, Germany
Most of these bubbles are round/spherical, e.g., [69], and bipolar structures are rare among the 24 μm bubbles. While this is consistent with the morphology of circumstellar gas nebulae of Wolf-Rayet stars, it seems to contradict the results found for LBV nebulae [52] which have as reported above a preference for bipolar morphologies
The Luminous Blue Variable phase is a short phase in the life of massive stars
Summary
Studying the brightest stars in M 31 and M 33 Hubble and Sandage [1] found irregular variable stars that defined a new object class: Var 19 in M 31 and Var 2, Var A, Var B and Vary C in M 33. All irregular variable stars Hubble and Sandage found showed the three common characteristics: high luminosity, blue color indice and at the date of observation an intermediate F-type spectrum. Observed bright stars in NGC 2366, NGC 4236, IC 2574, Ho I, Ho II, and NGC 2403 originally to further constrain the Hubble constant using Cepheids In some of these galaxies they identified stars they designated as Irregular Luminous Blue Variables. Lamers & Fitzpatrick [8] showed in a 1986 publication that —as still accepted —radiation and not turbulent pressure is the driver This linked Humphreys and Davidson observations to the fact that stars will become unstable in this cool and luminous state. S Dor Variables, P Cygni and η Car type stars, and explicitly excluded Wolf-Rayet stars and normal blue supergiants from LBVs
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