Variability of Blue Supergiants in the LMC with TESS

Ma 马, Linhao 林昊; Johnston, Cole; Bellinger, Earl Patrick; de Mink, Selma E.

doi:10.3847/1538-4357/ad38bc

ApJ

2024

DOI: 10.3847/1538-4357/ad38bc

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Variability of Blue Supergiants in the LMC with TESS

Linhao 林昊 Ma 马,

Cole Johnston,

Earl Patrick Bellinger

et al.

Abstract: The blue supergiant (BSG) problem, namely, the overabundance of BSGs inconsistent with classical stellar evolution theory, remains an open question in stellar astrophysics. Several theoretical explanations have been proposed, which may be tested by their predictions for the characteristic time variability. In this work, we analyze the light curves of a sample of 20 BSGs obtained from the Transiting Exoplanet Survey Satellite (TESS) mission. We report a characteristic signal in the low-frequency (f ≲ 2 day−1) r… Show more

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2024

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Cited by 3 publications

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Merger seismology: Distinguishing massive merger products from genuine single stars using asteroseismology

Henneco,

Schneider,

Hekker

et al. 2024

A&A

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Products of stellar mergers are predicted to be common in stellar populations and can potentially explain stars with peculiar properties. When the merger occurs after the initially more massive star has evolved into the Hertzsprung gap, the merger product may remain in the blue part of the Hertzsprung-Russell diagram for millions of years. Such objects could, therefore, explain the overabundance of observed blue stars, such as blue supergiants. However, it is currently not straightforward to distinguish merger products from genuine single stars or other stars with similar surface diagnostics. In this work, we made detailed asteroseismic comparisons between models of massive post-main-sequence merger products and genuine single stars to identify which asteroseismic diagnostics can be used to distinguish them. In doing so, we developed tools for the relatively young field of merger seismology. Genuine single stars in the Hertzsprung gap are fully radiative, while merger products have a convective He-burning core and convective H-burning shell while occupying similar locations in the Hertzsprung-Russell diagram. These major structural differences are reflected in lower asymptotic period spacing values for merger products and the appearance of deep dips in their period spacing patterns. Our genuine single-star models with masses above roughly 11.4 solar masses develop short-lived intermediate convective zones during their Hertzsprung gap evolution. This also leads to deep dips in their period spacing patterns. Because of the lack of a convective core, merger products and genuine single stars can be distinguished based on their asymptotic period spacing value in this mass range. We performed the comparisons with and without the effects of slow rotation included in the pulsation equations and conclude that the two types of stars are seismically distinguishable in both cases. The observability of the distinguishing asteroseismic features of merger products can now be assessed and exploited in practice.

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Merger seismology: Distinguishing massive merger products from genuine single stars using asteroseismology

Henneco,

Schneider,

Hekker

et al. 2024

A&A

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The ESO UVES/FEROS Large Programs of TESS OB pulsators

Serebriakova,

Tkachenko,

Aerts

2024

A&A

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Spectral lines of hot massive stars are known to exhibit large excess broadening in addition to rotational broadening. This excess broadening is often attributed to macroturbulence, whose physical origin is a matter of active debate in the stellar astrophysics community. We aim to shed light on the physical origin of macroturbulent line broadening by looking into the statistical properties of a large sample of O- and B-type stars both in the Galaxy and the Large Magellanic Cloud (LMC). We deliver newly measured macroturbulent velocities for 86 stars from the Galaxy in a consistent manner with 126 stars from the LMC. We composed a total sample of 594 stars with measured macroturbulent velocities by complementing our sample with archival data for the Galactic O- and B-type stars in order to gain better coverage of the parameter space. Furthermore, we computed an extensive grid of mesa models to compare, in a statistical manner, the predicted interior properties of stars (such as convection and wave propagation) with the inference of macroturbulent velocities from high-resolution spectroscopic observations. We find evidence for subsurface convective zones that formed in the iron opacity bump (FeCZ) being connected to observed macroturbulent velocities in hot massive stars. Additionally, we find the presence of two principally different regimes where, depending on the initial stellar mass, different mechanisms may be responsible for the observed excess line broadening. Stars with initial masses above 30$M_ odot $ exhibit macroturbulent velocities that are in line with FeCZ properties, as indicated by the trends in both observations and models. For stars below 12$M_ odot $, alternative mechanisms are needed to explain macroturbulent broadening, such as internal gravity waves (IGWs). Finally, in the intermediate range between 12 and 30$M_ odot $, IGWs tunnelling through subsurface convective layers combined with the presence of FeCZ-driven convection suggests that both processes could contribute to the observed macroturbulent velocities. This intermediate regime presents a region where the interplay between these two (or more) mechanisms remains to be fully understood.

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The Potential of Asteroseismology to Resolve the Blue Supergiant Problem

Bellinger,

de Mink,

van Rossem

et al. 2024

ApJL

Self Cite

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Despite major progress in our understanding of massive stars, concerning discrepancies still remain between observations and theory. Most notable are the numerous stars observed beyond the theoretical main sequence, an evolutionary phase expected to be short lived and hence sparsely populated. This is the “Blue Supergiant Problem.” Stellar models with abnormal internal structures can provide long-lived solutions for this problem: core hydrogen-burning stars with oversized cores may explain the hotter ones, and core helium-burning stars with undersized cores may explain the cooler ones. Such stars may result from enhanced or suppressed mixing in single stars or, more likely, as the products of binary interaction and stellar mergers. Here we investigate the potential of asteroseismology to uncover the nature of blue supergiants. We construct stellar models for the above scenarios and show that they predict g-mode period spacings that differ by an order of magnitude: ∼200 min versus ∼20 min for long-lived core H and He burning stars, respectively. For the classical scenario of H-shell-burning stars rapidly crossing the HG, we furthermore predict changes of the order of 10−2 μHz yr−1 in high-frequency modes; this effect would be in principle observable from ∼5 yr of asteroseismic monitoring if these modes can be identified. This raises the possibility of revealing the internal structure of blue supergiants and thus determining whether these stars are indeed binary merger products. These asteroseismic diagnostics may be measurable through long time-series observations from the ongoing TESS mission and upcoming PLATO mission, thereby laying a path toward resolving the blue supergiant problem.

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Variability of Blue Supergiants in the LMC with TESS

Cited by 3 publications

References 107 publications

Merger seismology: Distinguishing massive merger products from genuine single stars using asteroseismology

Merger seismology: Distinguishing massive merger products from genuine single stars using asteroseismology

The ESO UVES/FEROS Large Programs of TESS OB pulsators

The Potential of Asteroseismology to Resolve the Blue Supergiant Problem

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