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

Diaz, Sébastien; Apellániz, J. Maíz; Lennon, D. J.; Hernández, J. I. González; Prieto, C. Allende; Castro, N.; Burgos, A. de; Dufton, P. L.; Herrero, A.; Toledo-Padrón, B.; Smartt, S. J.

doi:10.1051/0004-6361/201937318

Cited by 38 publications

(59 citation statements)

References 33 publications

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“…They suggested that the unseen secondary component is a neutron star or a faint mainsequence star and that the primary star is a stripped helium star that lost its H-rich envelope due to a past binary masstransfer event. This claim was based on anomalous abundances derived for the star, consistent with processed material from the CNO cycle (enriched N, depleted C and O), also confirmed by Simón-Díaz et al (2020). A notable peculiarity that was consistently reported in the aforementioned studies is the sub-solar abundance derived for several heavy elements such as Mg, Si, and Fe, which are not expected to change throughout the evolution of the star.…”

Section: Introductionsupporting

confidence: 74%

“…Despite being fainter in the visual, the Be secondary is the more luminous component due to its higher temperature. We note that the comparable light contribution of the two components provides a natural explanation for the lack of evidence of binary motion in the Gaia astrometry (see Simón-Díaz et al 2020).…”

Section: B2 the Be-type Secondarymentioning

confidence: 75%

“…However, its nature remains unknown. Simón-Díaz et al (2020) performed a spectroscopic analysis of LB-1 while relaxing the assumption of local thermodynamic equilibrium (non-LTE). They classified the primary star as B6 IV and derived significantly lower values for the effective temperature (T eff = 14 kK) and surface gravity (log g = 3.5 [cgs]) compared with Liu et al (2019).…”

Section: Introductionmentioning

confidence: 99%

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The “hidden” companion in LB-1 unveiled by spectral disentangling

Shenar

Bodensteiner

Abdul-Masih

et al. 2020

A&A

117

144

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Context. The intriguing binary LS V +22 25 (LB-1) has drawn much attention following claims of it being a single-lined spectroscopic binary with a 79-day orbit comprising a B-type star and a ≈70 M⊙ black hole – the most massive stellar black hole reported to date. Subsequent studies demonstrated a lack of evidence for a companion of such great mass. Recent analyses have implied that the primary star is a stripped He-rich star with peculiar sub-solar abundances of heavy elements, such as Mg and Fe. However, the nature of the secondary, which was proposed to be a black hole, a neutron star, or a main sequence star, remains unknown. Aims. Based on 26 newly acquired spectroscopic observations secured with the HERMES and FEROS spectrographs covering the orbit of the system, we perform an orbital analysis and spectral disentangling of LB-1 to elucidate the nature of the system. Methods. To derive the radial velocity semi-amplitude K2 of the secondary and extract the spectra of the two components, we used two independent disentangling methods: the shift-and-add technique and Fourier disentangling with FDBinary. We used atmosphere models to constrain the surface properties and abundances. Results. Our disentangling and spectral analysis shows that LB-1 contains two components of comparable brightness in the optical. The narrow-lined primary, which we estimate to contribute ≈55% in the optical, has spectral properties that suggest that it is a stripped star: it has a small spectroscopic mass (≈1 M⊙) for a B-type star and it is He- and N-rich. Unlike previous reports, the abundances of heavy elements are found to be solar. The “hidden” secondary, which contributes about 45% of the optical flux, is a rapidly rotating (vsini ≈ 300 km s−1) B3 V star with a decretion disk – a Be star. As a result of its rapid rotation and dilution, the photospheric absorption lines of the secondary are not readily apparent in the individual observations. We measure a semi-amplitude for this star of K2 = 11.2 ± 1.0 km s−1 and adopting a mass of M2 = 7 ± 2 M⊙ typical for B3 V stars, we derive an orbital mass for the stripped primary of M1 = 1.5 ± 0.4 M⊙. The orbital inclination of 39 ± 4° implies a near-critical rotation for the Be secondary (veq ≈ 470 km s−1). Conclusions. LB-1 does not contain a compact object. Instead, it is a rare Be binary system consisting of a stripped star (the former mass donor) and a Be star rotating at near its critical velocity (the former mass accretor). This system is a clear example that binary interactions play a decisive role in the production of rapid stellar rotators and Be stars.

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Section: Introductionsupporting

confidence: 74%

Section: B2 the Be-type Secondarymentioning

confidence: 75%

Section: Introductionmentioning

confidence: 99%

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The “hidden” companion in LB-1 unveiled by spectral disentangling

Shenar

Bodensteiner

Abdul-Masih

et al. 2020

A&A

117

144

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“…El-Badry & Quataert (2020a) and Abdul-Masih et al (2020) showed that the anti-phase signature of Hα cannot be readily interpreted as Doppler motion without considering the impact of potential Hα absorption of the B-type component. Simón-Díaz et al (2020) and Irrgang et al (2020) performed spectroscopic studies of the primary and found evidence for processed CNO material in its atmosphere, leading Irrgang et al (2020) to suggest that it is a low-mass stripped helium star. Subsequently, Shenar et al (2020) utilised spectral disentangling to show that the secondary in LB-1 is not a BH, but a classical Be star -a rapidly rotating B-type star with a decretion disc (see e.g.…”

Section: Introductionmentioning

confidence: 99%

Is HR 6819 a triple system containing a black hole?

Bodensteiner

Shenar

Mahy

et al. 2020

A&A

106

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Context. HR 6819 was recently proposed to be a triple system consisting of an inner B-type giant plus black hole (BH) binary with an orbital period of 40 d and an outer Be tertiary. This interpretation is mainly based on two inferences: that the emission attributed to the outer Be star is stationary and that the inner star, which is used as mass calibrator for the BH, is a B-type giant. Aims. We re-investigate the properties of HR 6819 to search for a possibly simpler alternative explanation for HR 6819, which does not invoke the presence of a triple system with a BH in the inner binary. Methods. Based on an orbital analysis, the disentangling of the spectra of the two visible components and the atmosphere analysis of the disentangled spectra, we investigate the configuration of the system and the nature of its components. Results. Disentangling implies that the Be component is not a static tertiary, but rather a component of the binary in the 40 d orbit. The inferred radial velocity amplitudes of K1 = 60.4 ± 1.0 km s−1 for the B-type primary and K2 = 4.0 ± 0.8 km s−1 for the Be-type secondary imply an extreme mass ratio of M2/M1 = 15 ± 3. We find that the B-type primary, which we estimate to contribute about 45% to the optical flux, has an effective temperature of Teff = 16 ± 1 kK and a surface gravity of log g = 2.8 ± 0.2 [cgs], while the Be secondary, which contributes about 55% to the optical flux, has Teff = 20 ± 2 kK and log g = 4.0 ± 0.3 [cgs]. We infer spectroscopic masses of 0.4−0.1+0.3and 6−3+5 for the primary and secondary which agree well with the dynamical masses for an inclination of i = 32°. This indicates that the primary might be a stripped star rather than a B-type giant. Evolutionary modelling suggests that a possible progenitor system would be a tight (Pi ≈ 2 d) B+B binary system that experienced conservative mass transfer. While the observed nitrogen enrichment of the primary conforms with the predictions of the evolutionary models, we find no indications for the predicted He enrichment. Conclusions. We suggest that HR 6819 is a binary system consisting of a stripped B-type primary and a rapidly-rotating Be star that formed from a previous mass-transfer event. In the framework of this interpretation, HR 6819 does not contain a BH. Interferometry can distinguish between these two scenarios by providing an independent measurement of the separation between the visible components.

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“…这对经典的恒星演化理论提出了挑战. 该重要成果发表在Nature上 [26] , 论文发表后引起了众多国际团队的高度关注, 掀起了一场激烈的学术辩论 [27][28][29][30][31][32] . 对该结果的主要质疑有两处: 即其氢元素的发射线可能并非来自于随光学不可见天体运动的吸积盘, 而是来自于环绕该双星系统的外部气体盘 [27,29] ; 光学可见的那颗恒星可能并非B型星, 而是颗外壳层被剥离了的氦星 [30] .…”

Section: 中国科学院国家天文台刘继峰、张昊彤及其团队利用Lamost对kepler K2-0天区约3000颗恒星历时unclassified

Searching for stellar-mass black holes in the Milky Way

Gu¹,

Wu²,

Wang³

2021

Sci. Sin.-Phys. Mech. Astron.

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According to the stellar evolution model, 10 8-10 9 stellar-mass black holes (sMBHs) may exist in the Milky Way. However, only around 20 sMBHs have been dynamically confirmed. With the tremendous advancements in astronomical telescopes, new methods have been proposed to search for sMBHs. A large number of stellar spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) have enabled us to search for sMBHs through spectral analysis. This article reviews the 50-year history of sMBH search and introduces the classical method and some new methods on this issue. In particular, some recent studies based on LAMOST spectra are presented. Moreover, the prospects of sMBH search are discussed. black holes, spectroscopic binaries, X-ray binaries, parallaxes

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

Cited by 38 publications

References 33 publications

The “hidden” companion in LB-1 unveiled by spectral disentangling

The “hidden” companion in LB-1 unveiled by spectral disentangling

Is HR 6819 a triple system containing a black hole?

Searching for stellar-mass black holes in the Milky Way

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