*Review* **Luminous Blue Variables**

### **Kerstin Weis 1,\* and Dominik J. Bomans 1,2,3**


Received: 29 October 2019; Accepted: 18 February 2020; Published: 29 February 2020

**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 ge<sup>t</sup> 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.

**Keywords:** Luminous Blue Variables; giant eruption; massive stars; stellar population; Wolf-Rayet stars; Eddington limit; mass loss rate; nebulae of Luminous Blue Variable; Supernova impostors; bistability limit
