Luminous blue variables are antisocial: their isolation implies that they are kicked mass gainers in binary evolution

Abstract

Based on their relatively isolated environments, we argue that luminous blue variables (LBVs) must be primarily the product of binary evolution, challenging the traditional single-star view wherein LBVs mark a brief transition between massive O-type stars and Wolf-Rayet (WR) stars. If the latter were true, then LBVs should be concentrated in young massive clusters like early O-type stars. This is decidedly not the case. Examining locations of LBVs in our Galaxy and the Magellanic Clouds reveals that, with only a few exceptions, LBVs systematically avoid clusters of O-type stars. In the Large Magellanic Cloud, LBVs are statistically much more isolated than Otype stars, and (perhaps most surprisingly) even more isolated than WR stars. This makes it impossible for LBVs to be single "massive stars in transition" to WR stars. Instead, we propose that massive stars and supernova (SN) subtypes are dominated by bifurcated evolutionary paths in interacting binaries, wherein most WR stars and SNe Ibc correspond to the mass donors, while LBVs (and their lower-mass analogs like B[e] supergiants, which are even more isolated) are the mass gainers. In this view, LBVs are evolved massive blue stragglers. Through binary mass transfer, rejuvinated mass gainers get enriched, spun up, and sometimes kicked far from their clustered birthsites by their companion's SN. This scenario agrees better with LBVs exploding as Type IIn SNe in isolation, and it predicts that many massive runaway stars may be rapid rotators. Mergers or blue Thorne-Zykow-like objects might also give rise to LBVs, but these scenarios may have a harder time explaining why LBVs avoid clusters.

Helium stars: towards an understanding of Wolf–Rayet evolution

“…Recent work by Smith & Tombleson (2015) on luminous blue variable (LBV) stars provides additional evidence for WC stars being less massive than WN stars.…”

Dawes Review 6: The Impact of Companions on Stellar Evolution

“…Smith & Tombleson (2015) found that LBV stars are statistically more isolated than O and WR stars in the Galaxy and in Large Magellanic Cloud clusters, indicating that LBVs cannot in all cases be a phase in the evolution of O and WR stars. They proposed alternative binary scenarios for at least a fraction of the objects.…”

“…This discovery suggests that many massive star phenomena are related to the presence of a binary companion, for example, type Ib and Ic supernovae (Podsiadlowski, Joss, & Hsu, 1992;Smith et al, 2011a) or phenomena such as luminous blue variables (Smith & Tombleson, 2015). Additionally, the recent detection of gravitational waves has confirmed the existence of binary black holes (Abbott et al, 2016d), which are a likely end-product of the most massive binary evolution.…”

Core-collapse supernova progenitor constraints using the spatial distributions of massive stars in local galaxies

“…In M33, there are only four confirmed LBVs (Hubble-Sandage variables B, C and 2 and Var 83; Humphreys et al 2014), but we include them as well (the actual number of LBV stars in M33 was estimated to be in the hundreds by Massey et al 2007). As Smith & Tombleson (2015) (Wenger et al 2000), with a search radius of 5 degrees from the centre of the LMC as reported in NED. With such a search we have obtained the coordinates of main-sequence stars between the B2V and O3V spectral types as reported in April 2015.…”

“…A12 argued that while the diversity within the subtype allows for some progenitors to be LBVs, most IIn progenitors are instead lower-mass stars, such as asymptotic giant branch (AGB) stars exploding as electron-capture SNe. To reconcile this with the identified massive LBV progenitors of type IIn SNe, Smith & Tombleson (2015) examined the LBVs in the Large Magellanic Cloud (LMC) and found them to be relatively isolated from O-type stars, which was argued to at least partially explain the weak correlation with H α emission for the SNe. However, Humphreys et al (2016) pointed out that this LBV sample included both classical and lower-luminosity Original continuum-subtracted H α intensity maps used in this study: the LMC on the left (from the SHASSA survey; Gaustad et al 2001) and M33 on the right (Hoopes & Walterbos 2000), cropped in the case of the LMC but otherwise unaltered.…”