On the Gaia DR2 distances for Galactic Luminous Blue Variables

TL;DR

This study analyzes Gaia DR2 parallaxes for Galactic LBVs, revealing significant differences from previous distances, a broader luminosity range, and implications for LBV evolution, instability, and their role as supernova progenitors.

Contribution

It provides the first comprehensive Gaia DR2-based distance analysis for Galactic LBVs, challenging previous assumptions about their luminosity distribution and instability.

Findings

Gaia DR2 distances often differ from literature values, sometimes being smaller.

LBVs occupy a wide luminosity and temperature range, including low-luminosity objects.

Implications for LBV instability, binary evolution, and supernova progenitors are discussed.

Abstract

We examine parallaxes and distances for Galactic luminous blue variables (LBVs) in Gaia DR2. The sample includes 11 LBVs and 14 LBV candidates. For about half of the sample, DR2 distances are either similar to commonly adopted literature values, or the DR2 values have large uncertainties. For the rest, reliable DR2 distances differ significantly from values in the literature, and in most cases the Gaia DR2 distance is smaller. Two key results are that the S Doradus instability strip may not be as clearly defined as previously thought, and that there exists a population of LBVs at relatively low luminosities. LBVs seem to occupy a wide swath from the end of the main sequence at the blue edge to 8000 K at the red side, with a spread in luminosity reaching as low as log(L/Lsun)=4.5. The lower-luminosity group corresponds to effective single-star initial masses of 10-25 Msun, and includes objects that have been considered as confirmed LBVs. We discuss implications for LBVs including (1) their instability and origin in binary evolution, (2) connections to some supernova (SN) impostors such as the class of SN 2008S-like objects, and (3) LBVs that may be progenitors of SNe with dense circumstellar material across a wide initial mass range. Although some of the Gaia DR2 distances for LBVs have large uncertainty, this represents the most direct and consistent set of Galactic LBV distance estimates available in the literature.