On the Social Traits of Luminous Blue Variables

Abstract

In a recent paper, Smith & Tombleson (2015) state that the Luminous Blue Variables (LBVs ) in the Milky Way and the Magellanic Clouds are isolated; that they are not spatially associated with young O-type stars. They propose a novel explanation that would overturn the standard view of LBVs. In this paper we test their hypothesis for the LBVs in M31 and M33 as well as the LMC and SMC. We show that in M31 and M33, the LBVs are associated with luminous young stars and supergiants appropriate to their luminosities and positions on the HR Diagram. Moreover, in the Smith and Tombleson scenario most of the LBVs should be runaway stars, but the stars' velocities are consistent with their positions in the respective galaxies. In the Magellanic Clouds, those authors' sample was a mixed population. We reassess their analysis, removing seven stars that have no clear relation to LBVs. When we separate the more massive classical and the less luminous LBVs, the classical LBVs have a distribution similar to the late O-type stars, while the less luminous LBVs have a distribution like the red supergiants. None of the confirmed LBVs have high velocities or are candidate runaway stars. These results support the accepted description of LBVs as evolved massive stars that have shed a lot of mass, and are now close to their Eddington limit.

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

“…These include all confirmed LBVs in the LMC and likely, wellstudied LBV candidates with shells. We exclude the five unrelated stars and the duplicate entry pointed out by Humphreys et al (2016), bringing the total number to ten LBVs -three classical LBVs and seven lower-luminosity LBVs. 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).…”

“…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. North is up and east is left.…”

Luminous and Variable Stars in M31 and M33. V. The Upper HR Diagram

“…Humphreys et al (2016) showed that the confirmed LBVs in M31 and M33 were found primarily in stellar groups. We have added information about the stars' spatial identification with stellar groups such as known H II regions and Associations to Tables 2 and 3.…”

“…LBVs are distinguished from the normal supergiants that occupy the same locus in the luminosity-temperature space by their proximity to the Eddington limit. They have high L/M ratios, and their Eddington factor Γ = L/L Edd is high, 0.5 or higher due to high mass loss events as hot supergiants for stars with initial masses ≥ 40 -50 M ⊙ or as red supergiants for the less luminous LBVs; see Figure 1 and the discussions in Humphreys et al (2016) and .…”

“…We also re-examined the extinction estimates for the stars in Paper II and they are included here. Differences in the parameters for the confirmed LBVs in Paper II and Humphreys et al (2016) are due to minor adjustments in the adopted extinction. To estimate their intrinsic luminosities and their surface temperatures, we integrate their extinction-corrected SEDs.…”