Kinematic Insights Into Luminous Blue Variables and B[e] Supergiants

TL;DR

This study uses Gaia DR3 data to analyze the motions of luminous blue variables and B[e] supergiants in the Magellanic Clouds, revealing their kinematic differences and implications for their origins and binary interactions.

Contribution

It provides the first proper-motion based kinematic analysis of LBVs and sgB[e] stars, distinguishing subclasses and their possible evolutionary pathways.

Findings

Class 1 LBVs and sgB[e] stars have velocities similar to SMC field OBe stars.

Class 2 LBVs show no signs of acceleration, suggesting they are single or pre-SN stars.

sgB[e] stars are faster in the SMC than in the LMC, possibly due to lower metallicity effects.

Abstract

Recent work suggests that many luminous blue variables (LBVs) and B[e] supergiants (sgB[e]) are isolated, implying that they may be products of massive binaries, kicked by partner supernovae (SNe). However, the evidence is somewhat complex and controversial. To test this scenario, we measure the proper-motion velocities for these objects in the LMC and SMC, using Gaia Data Release 3. Our LMC results show that the kinematics, luminosities, and IR properties point to LBVs and sgB[e] stars being distinct classes. We find that Class 1 LBVs, which have dusty nebulae, and sgB[e] stars both show velocity distributions comparable to that of SMC field OBe stars, which are known to have experienced SN kicks. The sgB[e] stars are faster, plausibly due to their lower average masses. However, Class 2 LBVs, which are luminous objects without dusty nebulae, show no signs of acceleration, therefore suggesting that they are single stars, pre-SN binaries, or perhaps binary mergers. The candidate LBV Class 3 stars, which are dominated by hot dust, are all confirmed sgB[e] stars; their luminosities and velocities show that they simply represent the most luminous and massive of the sgB[e] class. There are very few SMC objects, but the sgB[e] stars are faster than their LMC counterparts, which may be consistent with expectations that lower-metallicity binaries are tighter, causing faster ejections. We also examine the distinct class of dust-free, weak-lined sgB[e] stars, finding that the SMC objects have the fastest velocities of the entire sample.