## Properties of OB star-black hole systems derived from detailed binary evolution models

Langer, N.; Schürmann, C.; Stoll, K.; Marchant, P.; Lennon, D. J.; Mahy, L.; de Mink, S. E.; Quast, M.; Riedel, W.; Sana, H.; Schneider, P.; Schootemeijer, A.; Wang, C.; Almeida, L. A.; Bestenlehner, J. M.; Bodensteiner, J.; Castro, N.; Clark, S.; Crowther, P. A.; Dufton, P. Evans, C. J.; Fossati, L.; Gräfener, G.; Grassitelli, L.; Grin, N.; Hastings, B.; Herrero, A.; de Koter, A.; Menon, A.; Patrick, L.; Puls, J.; Renzo, M.; Sander, A. A. C.; Schneider, F. R. N.; Sen, K.; Shenar, T.; Simón-Días, S.; Tauris, T. M.; Tramper, F.; Vink, J. S.; Xu, X. -T.

Astronomy & Astrophysics, Volume 638, A39 (2020)

#### Abstract

Context. The recent gravitational wave measurements have demonstrated the existence of stellar mass black hole binaries. It is essential for our understanding of massive star evolution to identify the contribution of binary evolution to the formation of double black holes.
Aims: A promising way to progress is investigating the progenitors of double black hole systems and comparing predictions with local massive star samples, such as the population in 30 Doradus in the Large Magellanic Cloud (LMC).
Methods: With this purpose in mind, we analysed a large grid of detailed binary evolution models at LMC metallicity with initial primary masses between 10 and 40 M, and identified the model systems that potentially evolve into a binary consisting of a black hole and a massive main-sequence star. We then derived the observable properties of such systems, as well as peculiarities of the OB star component.
Results: We find that ∼3% of the LMC late-O and early-B stars in binaries are expected to possess a black hole companion when stars with a final helium core mass above 6.6 M are assumed to form black holes. While the vast majority of them may be X-ray quiet, our models suggest that these black holes may be identified in spectroscopic binaries, either by large amplitude radial velocity variations (≳50 km s-1) and simultaneous nitrogen surface enrichment, or through a moderate radial velocity (≳10 km s-1) and simultaneous rapid rotation of the OB star. The predicted mass ratios are such that main-sequence companions can be excluded in most cases. A comparison to the observed OB+WR binaries in the LMC, Be and X-ray binaries, and known massive black hole binaries supports our conclusion.
Conclusions: We expect spectroscopic observations to be able to test key assumptions in our models, with important implications for massive star evolution in general and for the formation of double black hole mergers in particular.

Keywords: stars: evolution;stars: massive;binaries: close;stars: black holes;stars: early-type;stars: rotation;Astrophysics – Solar and Stellar Astrophysics;Astrophysics – High Energy Astrophysical Phenomena

## The Tarantula Massive Binary Monitoring. IV. Double-lined photometric binaries

Mahy, L.; Almeida, L. A.; Sana, H.; Clark, J. S.; de Koter, A.; de Mink, S. E.; Evans, C. J.; Grin, N. J.; Langer, N.; Moffat, A. F. J.; Schneider, F. R. N.; Shenar, T.; Tramper, F.

Astronomy & Astrophysics, Volume 634, A119 (2020)

#### Abstract

Context. A high fraction of massive stars are found to be binaries but only a few of them are reported as photometrically variable. By studying the populations of double-lined spectroscopic binaries in the 30 Doradus region, we found a subset of them that have photometry from the OGLE project and that display variations in their light curves related to orbital motions.
Aims: The goal of this study is to determine the dynamical masses and radii of the 26 binary components in order to investigate the mass-discrepancy problem and to provide an empirical mass-luminosity relation for the Large Magellanic Cloud (LMC).
Methods: We use the PHOEBE programme to perform a systematic analysis of the OGLE V and I light curves obtained for 13 binary systems in the 30 Doradus region. We adopt the effective temperatures, and orbital parameters derived previously to obtain the inclinations of the systems and the parameters of the individual components.
Results: Three systems display eclipses in their light curves, while the others only display ellipsoidal variations. We classify two systems as over-contact, five as semi-detached, and four as detached. The two remaining systems have uncertain configurations due to large uncertainties on their inclinations. The fact that systems display ellipsoidal variations has a significant impact on the inclination errors. From the dynamical masses, luminosities, and radii, we provide LMC-based empirical mass-luminosity and mass-radius relations, and we compare them to other relations given for the Galaxy, the LMC, and the Small Magellanic Cloud. These relations differ for different mass ranges, but do not seem to depend on the metallicity regimes. We also compare the dynamical, spectroscopic, and evolutionary masses of the stars in our sample. While the dynamical and spectroscopic masses agree with each other, the evolutionary masses are systematically higher, at least for stars in semi-detached systems. This suggests that the mass discrepancy can be partly explained by past or ongoing interactions between the stars.

Keywords: stars: early-type;binaries: eclipsing;open clusters and associations: individual: 30 Doradus;stars: fundamental parameters;Astrophysics – Solar and Stellar Astrophysics

## The Tarantula Massive Binary Monitoring. III. Atmosphere analysis of double-lined spectroscopic systems

Mahy, L.; Sana, H.; Abdul-Masih, M.; Almeida, L. A.; Langer, N.; Shenar, T.; de Koter, A.; de Mink, S. E.; de Wit, S.; Grin, N. J.; Evans, C. J.; Moffat, A. F. J.; Schneider, F. R. N.; Barbá, R.; Clark, J. S.; Crowther, P.; Gräfener, G.; Lennon, D. J.; Tramper, F.; Vink, J. S.

Astronomy & Astrophysics, Volume 634, A118 (2020)

#### Abstract

Context. Accurate stellar parameters of individual objects in binary systems are essential to constrain the effects of binarity on stellar evolution. These parameters serve as a prerequisite to probing existing and future theoretical evolutionary models.
Aims: We aim to derive the atmospheric parameters of the 31 double-lined spectroscopic binaries in the Tarantula Massive Binary Monitoring sample. This sample, composed of detached, semi-detached and contact systems with at least one of the components classified as an O-type star, is an excellent test-bed to study how binarity can impact our knowledge of the evolution of massive stars.
Methods: In the present paper, 32 epochs of FLAMES/GIRAFFE spectra are analysed by using spectral disentangling to construct the individual spectra of 62 components. We then apply the CMFGEN atmosphere code to determine their stellar parameters and their helium, carbon, and nitrogen surface abundances.
Results: Among the 31 systems that we study in the present paper, we identify between 48 and 77% of them as detached, likely pre-interacting systems, 16% as semi-detached systems, and between 5 and 35% as systems in or close to contact phase. Based on the properties of their components, we show that the effects of tides on chemical mixing are limited. Components on longer-period orbits show higher nitrogen enrichment at their surface than those on shorter-period orbits, in contrast to expectations of rotational or tidal mixing, implying that other mechanisms play a role in this process. For semi-detached systems, components that fill their Roche lobe are mass donors. They exhibit higher nitrogen content at their surface and rotate more slowly than their companions. By accreting new material, their companions spin faster and are likely rejuvenated. Their locations in the N – v sin i diagram tend to show that binary products are good candidates to populate the two groups of stars (slowly rotating, nitrogen-enriched objects and rapidly rotating non-enriched objects) that cannot be reproduced through single-star population synthesis. Finally, we find no peculiar surface abundances for the components in (over-)contact systems, as has been suggested by evolutionary models for tidal mixing.
Conclusions: This sample, consisting of 31 massive binary systems, is the largest sample of binaries composed of at least one O-type star to be studied in such a homogeneous way by applying spectral disentangling and atmosphere modelling. The study of these objects gives us strong observational constraints to test theoretical binary evolutionary tracks.

Keywords: stars: early-type;binaries: spectroscopic;open clusters and associations: individual: 30 Doradus;stars: fundamental parameters;Astrophysics – Solar and Stellar Astrophysics;Astrophysics – Astrophysics of Galaxies

## The young massive SMC cluster NGC 330 seen by MUSE. I. Observations and stellar content

Bodensteiner, J.; Sana, H.; Mahy, L.; Patrick, L. R.; de Koter, A.; de Mink, S. E.; Evans, C. J.; Götberg, Y.; Langer, N.; Lennon, D. J.; Schneider, F. R. N.; Tramper, F.

Astronomy & Astrophysics, Volume 634, A51 (2020)

#### Abstract

Context. A majority of massive stars are part of binary systems, a large fraction of which will inevitably interact during their lives. Binary-interaction products (BiPs), that is, stars affected by such interaction, are expected to be commonly present in stellar populations. BiPs are thus a crucial ingredient in the understanding of stellar evolution.
Aims: We aim to identify and characterize a statistically significant sample of BiPs by studying clusters of 10 – 40 Myr, an age at which binary population models predict the abundance of BiPs to be highest. One example of such a cluster is NGC 330 in the Small Magellanic Cloud.
Methods: Using MUSE WFM-AO observations of NGC 330, we resolved the dense cluster core for the first time and were able to extract spectra of its entire massive star population. We developed an automated spectral classification scheme based on the equivalent widths of spectral lines in the red part of the spectrum.
Results: We characterize the massive star content of the core of NGC 330, which contains more than 200 B stars, 2 O stars, 6 A-type supergiants, and 11 red supergiants. We find a lower limit on the Be star fraction of 32 ± 3% in the whole sample. It increases to at least 46 ± 10% when we only consider stars brighter than V = 17 mag. We estimate an age of the cluster core between 35 and 40 Myr and a total cluster mass of 88-18+17 × 103 M.
Conclusions: We find that the population in the cluster core is different than the population in the outskirts: while the stellar content in the core appears to be older than the stars in the outskirts, the Be star fraction and the observed binary fraction are significantly higher. Furthermore, we detect several BiP candidates that will be subject of future studies.

Keywords: stars: massive;stars: emission-line;Be;binaries: spectroscopic;blue stragglers;Magellanic Clouds;open clusters and associations: individual: NGC 330;Astrophysics – Solar and Stellar Astrophysics;Astrophysics – Astrophysics of Galaxies

## Discovery of a Red Supergiant Donor Star in SN2010da/NGC 300 ULX-1

Heida, M.; Lau, R. M.; Davies, B.; Brightman, M.; Fürst, F.; Grefenstette, B. W.; Kennea, J. A.; Tramper, F.; Walton, D. J.; Harrison, F. A.

The Astrophysical Journal Letters, Volume 883, L34 (2019)

#### Abstract

SN2010da/NGC 300 ULX-1 was first detected as a supernova impostor in 2010 May and was recently discovered to be a pulsating ultraluminous X-ray source. In this Letter, we present Very Large Telescope/X-shooter spectra of this source obtained in 2018 October, covering the wavelength range 350-2300 nm. The J- and H-bands clearly show the presence of a red supergiant (RSG) donor star that is best matched by a MARCS stellar atmosphere with T eff = 3650-3900 K and log(L bol/L ) = 4.25 ± 0.10, which yields a stellar radius R = 310 ± 70R . To fit the full spectrum, two additional components are required: a blue excess that can be fitted either by a hot blackbody (T ≳ 20,000 K) or a power law (spectral index α ≈ 4) and is likely due to X-ray emission reprocessed in the outer accretion disk or the donor star; and a red excess that is well fitted by a blackbody with a temperature of ̃1100 K, and is likely due to warm dust in the vicinity of SN2010da. The presence of an RSG in this system implies an orbital period of at least 0.8-2.1 yr, assuming Roche-lobe overflow. Given the large donor-to-compact object mass ratio, orbital modulations of the radial velocity of the RSG are likely undetectable. However, the radial velocity amplitude of the neutron star is large enough (up to 40-60 km s-1) to potentially be measured in the future, unless the system is viewed at a very unfavorable inclination.

Keywords: High mass X-ray binary stars;Late-type supergiant stars;Neutron stars;Astrophysics – High Energy Astrophysical Phenomena;Astrophysics – Astrophysics of Galaxies;Astrophysics – Solar and Stellar Astrophysics