A detailed non-LTE analysis of LB-1: Revised parameters and surface abundances

Context. It has recently been proposed that LB-1 is a binary system at 4 kpc consisting of a B-type star of 8 M⊙ and a massive stellar black hole (BH) of 70 M⊙. This finding challenges our current theories of massive star evolution and formation of BHs at solar metallicity. Aims. Our objective is to derive the effective temperature, surface gravity, and chemical composition of the B-type component in order to determine its nature and evolutionary status and, indirectly, to constrain the mass of the BH. Methods. We use the non-LTE stellar atmosphere code FASTWIND to analyze new and archival high-resolution data. Results. We determine (Teff, log g) values of (14 000 ± 500 K, 3.50 ± 0.15 dex) that, combined with the Gaia parallax, imply a spectroscopic mass, from log g, of 3.2+2.1−1.9 M⊙ and an evolutionary mass, assuming single star evolution, of 5.2+0.3−0.6 M⊙. We determine an upper limit of 8 km s−1 for the projected rotational velocity and derive the surface abundances; we find the star to have a silicon abundance below solar, and to be significantly enhanced in nitrogen and iron and depleted in carbon and magnesium. Complementary evidence derived from a photometric extinction analysis and Gaia yields similar results for Teff and log g and a consistent distance around 2 kpc. Conclusions. We propose that the B-type star is a slightly evolved main sequence star of 3–5 M⊙ with surface abundances reminiscent of diffusion in late B/A chemically peculiar stars with low rotational velocities. There is also evidence for CN-processed material in its atmosphere. These conclusions rely critically on the distance inferred from the Gaia parallax. The goodness of fit of the Gaia astrometry also favors a high-inclination orbit. If the orbit is edge-on and the B-type star has a mass of 3–5 M⊙, the mass of the dark companion would be 4–5 M⊙, which would be easier to explain with our current stellar evolutionary models.

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The Physical Parameters of Four WC-type Wolf–Rayet Stars in the Large Magellanic Cloud: Evidence of Evolution*

The Astrophysical Journal ◽

10.3847/1538-4357/ac3426 ◽

2022 ◽

Vol 924 (2) ◽

pp. 44

Author(s):

Erin Aadland ◽

Philip Massey ◽

D. John Hillier ◽

Nidia Morrell

Keyword(s):

Spectral Synthesis ◽

Mass Loss Rate ◽

Large Magellanic Cloud ◽

Stellar Atmosphere ◽

Magellanic Cloud ◽

Physical Parameters ◽

Evolutionary Models ◽

Single Star ◽

Oxygen Abundance ◽

Solar Metallicity

Abstract We present a spectral analysis of four Large Magellanic Cloud (LMC) WC-type Wolf–Rayet (WR) stars (BAT99-8, BAT99-9, BAT99-11, and BAT99-52) to shed light on two evolutionary questions surrounding massive stars. The first is: are WO-type WR stars more oxygen enriched than WC-type stars, indicating further chemical evolution, or are the strong high-excitation oxygen lines in WO-type stars an indication of higher temperatures. This study will act as a baseline for answering the question of where WO-type stars fall in WR evolution. Each star’s spectrum, extending from 1100 to 25000 Å, was modeled using cmfgen to determine the star’s physical properties such as luminosity, mass-loss rate, and chemical abundances. The oxygen abundance is a key evolutionary diagnostic, and with higher resolution data and an improved stellar atmosphere code, we found the oxygen abundance to be up to a factor of 5 lower than that of previous studies. The second evolutionary question revolves around the formation of WR stars: do they evolve by themselves or is a close companion star necessary for their formation? Using our derived physical parameters, we compared our results to the Geneva single-star evolutionary models and the Binary Population and Spectral Synthesis (BPASS) binary evolutionary models. We found that both the Geneva solar-metallicity models and BPASS LMC-metallicity models are in agreement with the four WC-type stars, while the Geneva LMC-metallicity models are not. Therefore, these four WC4 stars could have been formed either via binary or single-star evolution.

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Massive star evolution revealed in the Mass-Luminosity plane

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319001170 ◽

2018 ◽

Vol 14 (S346) ◽

pp. 480-485

Author(s):

Erin R. Higgins ◽

Jorick S. Vink

Keyword(s):

Mass Loss ◽

Stellar Evolution ◽

Massive Star ◽

Main Sequence ◽

Theoretical Models ◽

Physical Processes ◽

Single Star ◽

Star Evolution ◽

Novel Method ◽

Massive Star Evolution

AbstractMassive star evolution is dominated by key physical processes such as mass loss, convection and rotation, yet these effects are poorly constrained, even on the main sequence. We utilise a detached, eclipsing binary HD166734 as a testbed for single star evolution to calibrate new MESA stellar evolution grids. We introduce a novel method of comparing theoretical models with observations in the ‘Mass-Luminosity Plane’, as an equivalent to the HRD (see Higgins & Vink 2018). We reproduce stellar parameters and abundances of HD166734 with enhanced overshooting (αov=0.5), mass loss and rotational mixing. When comparing the constraints of our testbed to the systematic grid of models we find that a higher value of αov=0.5 (rather than αov=0.1) results in a solution which is more likely to evolve to a neutron star than a black hole, due to a lower value of the compactness parameter.

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Massive star evolution in the Small Magellanic Cloud

Symposium - International Astronomical Union ◽

10.1017/s0074180900212370 ◽

2003 ◽

Vol 212 ◽

pp. 308-315 ◽

Cited By ~ 2

Author(s):

Daniel J. Lennon

Keyword(s):

Stellar Evolution ◽

Massive Star ◽

Main Sequence ◽

Single Star ◽

Promising Alternative ◽

Star Models ◽

Abundance Patterns ◽

Star Evolution ◽

Type Giant ◽

Massive Star Evolution

We discuss abundances for eight early B-type giant/supergiant stars in the SMC cluster NGC 330. All are nitrogen rich with an abundance approximately 1.3 dex higher than an SMC main-sequence field. Given the number of B-type stars with low rotational projected velocities in NGC 330 (all our targets have v sin i < 50 kms–1), we suggest that it is unlikely that the stars in our sample are seen almost pole-on, but rather that they are intrinsically slow rotators. Comparing these results with the predictions of stellar evolution models including the effects of rotationally induced mixing, we conclude that while the abundance patterns may indeed be reproduced, those models with initially large rotational velocities do not reproduce the observed range of effective temperatures of our sample, nor the currently observed rotational velocities. Binary models may be able to produce stars in the observed temperature range and provide a promising alternative to single star models for explaining the observations. We also discuss the clear need for stellar evolution calculations employing the correct chemical mix of carbon, nitrogen and oxygen for the SMC.

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Testing how massive stars evolve, lose mass, and collapse at low metal content

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319001297 ◽

2018 ◽

Vol 14 (S346) ◽

pp. 98-101

Author(s):

Eliceth Y. Rojas Montes ◽

Jorick Vink

Keyword(s):

Massive Star ◽

Massive Stars ◽

Stellar Atmospheres ◽

Evolutionary Status ◽

Hole Formation ◽

Complete Sample ◽

Star Evolution ◽

Theoretical Predictions ◽

Low Metallicity ◽

Massive Star Evolution

AbstractIn order to test massive star evolution above 25 M⊙, we perform spectral analysis on a sample of massive stars in the Small Magellanic Cloud that includes both O stars as well as more evolved Wolf-Rayet stars. We present a grid of non-LTE stellar atmospheres that has been calculated using the cmfgen code, in order to have a systematic and homogeneous approach. We obtain stellar and wind parameters for O stars, spectral types ranging from O2 to O6, and the complete sample of known Wolf-Rayet stars. We discuss the evolutionary status of both the O and WR stars and the links between them, as well as the most likely evolutionary path towards black hole formation in a low metallicity environment, including testing theoretical predictions for mass-loss rates at low metallicities.

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Formation rate of LB-1-like systems through dynamical interactions

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa021 ◽

2020 ◽

Vol 72 (3) ◽

Cited By ~ 3

Author(s):

Ataru Tanikawa ◽

Tomoya Kinugawa ◽

Jun Kumamoto ◽

Michiko S Fujii

Keyword(s):

Open Cluster ◽

Formation Rate ◽

Open Clusters ◽

Type Star ◽

Dynamical Mechanism ◽

Milky Way Galaxy ◽

Triple Systems ◽

Stellar Collisions ◽

Solar Metallicity ◽

Helium Star

Abstract We estimate formation rates of LB-1-like systems through dynamical interactions in the framework of the theory of stellar evolution before the discovery of the LB-1 system. The LB-1 system contains a ∼70 ${M_{\odot}}$ black hole (BH), a so-called pair instability (PI) gap BH, and a B-type star with solar metallicity, and has nearly zero eccentricity. The most efficient formation mechanism is as follows. In an open cluster, a naked helium star (with ∼20 ${M_{\odot}}$) collides with a heavy main sequence star (with ∼50 ${M_{\odot}}$) which has a B-type companion. The collision results in a binary consisting of the collision product and the B-type star with a high eccentricity. The binary can be circularized through the dynamical tide with radiative damping of the collision product envelope. Finally, the collision product collapses to a PI-gap BH, avoiding pulsational pair instability and pair instability supernovae because its He core is as massive as the pre-colliding naked He star. We find that the number of LB-1-like systems in the Milky Way galaxy is ∼0.01(ρoc/104 ${M_{\odot}}$ pc−3), where ρoc is the initial mass densities of open clusters. If we take into account LB-1-like systems with O-type companion stars, the number increases to ∼0.03(ρoc/104 ${M_{\odot}}$ pc−3). This mechanism can form LB-1-like systems at least ten times more efficiently than the other mechanisms: captures of B-type stars by PI-gap BHs, stellar collisions between other types of stars, and stellar mergers in hierarchical triple systems. We conclude that no dynamical mechanism can explain the presence of the LB-1 system.

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Outflowing Envelopes From Stars at Arbitrary Optical Depths a New Approach to the Problem

Highlights of Astronomy ◽

10.1017/s1539299600021316 ◽

1998 ◽

Vol 11 (1) ◽

pp. 381-381

Author(s):

A.V. Dorodnitsyn

Keyword(s):

Differential Equations ◽

Massive Star ◽

System Of Differential Equations ◽

Continuous Transition ◽

Satisfactory Description ◽

Sonic Point ◽

New Approach ◽

Star Evolution ◽

Matter Flux ◽

Massive Star Evolution

We have considered a stationary outflowing envelope accelerated by the radiative force in arbitrary optical depth case. Introduced approximations provide satisfactory description of the behavior of the matter flux with partially separated radiation at arbitrary optical depths. The obtained systemof differential equations provides a continuous transition of the solution between optically thin and optically thick regions. We analytically derivedapproximate representation of the solution at the vicinity of the sonic point. Using this representation we numerically integrate the system of equations from the critical point to the infinity. Matching the boundary conditions we obtain solutions describing the problem system of differential equations. The theoretical approach advanced in this work could be useful for self-consistent simulations of massive star evolution with mass loss.

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Four open questions in massive star evolution

EAS Publications Series ◽

10.1051/eas/1363042 ◽

2013 ◽

Vol 63 ◽

pp. 373-383 ◽

Cited By ~ 2

Author(s):

G. Meynet ◽

P. Eggenberger ◽

S. Ekström ◽

C. Georgy ◽

J. Groh ◽

...

Keyword(s):

Massive Star ◽

Star Evolution ◽

Open Questions ◽

Massive Star Evolution

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Hydrodynamic Processes in Massive Stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308023466 ◽

2008 ◽

Vol 4 (S252) ◽

pp. 439-449 ◽

Cited By ~ 3

Author(s):

Casey A. Meakin

Keyword(s):

Stellar Evolution ◽

Magnetized Plasma ◽

Mixing Properties ◽

New Era ◽

Linear Set ◽

Star Evolution ◽

Hydrodynamic Processes ◽

Stellar Interiors ◽

Transport And Mixing ◽

Massive Star Evolution

AbstractThe hydrodynamic processes operating within stellar interiors are far richer than represented by the best stellar evolution model available. Although it is now widely understood, through astrophysical simulation and relevant terrestrial experiment, that many of the basic assumptions which underlie our treatments of stellar evolution are flawed, we lack a suitable, comprehensive replacement. This is due to a deficiency in our fundamental understanding of the transport and mixing properties of a turbulent, reactive, magnetized plasma; a deficiency in knowledge which stems from the richness and variety of solutions which characterize the inherently non-linear set of governing equations. The exponential increase in availability of computing resources, however, is ushering in a new era of understanding complex hydrodynamic flows; and although this field is still in its formative stages, the sophistication already achieved is leading to a dramatic paradigm shift in how we model astrophysical fluid dynamics. We highlight here some recent results from a series of multi-dimensional stellar interior calculations which are part of a program designed to improve our one-dimensional treatment of massive star evolution and stellar evolution in general.

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