Eta Carinae and the Luminous Blue Variables

TL;DR

This paper examines the properties, variability, and evolutionary status of luminous blue variables, including Eta Carinae, revealing their broader luminosity range, diverse behaviors, and potential pre-supernova phase.

Contribution

It broadens the understanding of LBV luminosities, variability types, and discusses their possible evolution into pre-supernova stages, challenging existing paradigms.

Findings

LBV phenomenon extends to lower luminosities than previously thought

Giant eruptions are likely related to S Doradus variability

Some LBVs may be in a pre-supernova evolutionary stage

Abstract

We evaluate the place of Eta Carinae amongst the class of luminous blue variables (LBVs) and show that the LBV phenomenon is not restricted to extremely luminous objects like Eta Car, but extends luminosities as low as log(L/Lsun) = 5.4 - corresponding to initial masses ~25 Msun, and final masses as low as ~10-15 Msun. We present a census of S Doradus variability, and discuss basic LBV properties, their mass-loss behaviour, and whether at maximum light they form pseudo-photospheres. We argue that those objects that exhibit giant Eta Car-type eruptions are most likely related to the more common type of S Doradus variability. Alternative atmospheric models as well as sub-photospheric models for the instability are presented, but the true nature of the LBV phenomenon remains as yet elusive. We end with a discussion on the evolutionary status of LBVs - highlighting recent indications that some LBVs may be in a direct pre-supernova state, in contradiction to the standard paradigm for massive star evolution.