The young massive SMC cluster NGC 330 seen by MUSE

et al. 2022

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Context. Massive binaries hosting a black hole (OB+BH) represent a critical phase in the production of BH mergers in the context of binary evolution. In spite of this, such systems have so far largely avoided detection. Single-lined spectroscopic (SB1) O-type binaries are ideal objects to search for elusive BH companions. Moreover, SB1 binaries hosting two main sequence stars probe a regime of more extreme mass ratios and longer periods compared to double-lined binaries (SB2), and are thus valuable for establishing the natal mass ratio distribution of massive stars. Aims. We characterise the hidden companions in 51 SB1 O-type and evolved B-type binaries identified in the Large Magellanic Cloud (LMC) in the framework of the VLT-FLAMES Tarantula Survey (VFTS) and its follow-up, the Tarantula Massive Binary Monitoring (TMBM). The binaries cover periods between few days to years (0 < log P < 3 [d]). Goals are to hunt for BHs and sample the low-mass end of the mass-ratio distribution. Methods. To uncover the hidden companions, we implement the shift-and-add grid disentangling algorithm on 32 epochs of spectroscopy acquired in the framework of TMBM with the FLAMES spectrograph, allowing us to detect companions contributing as little as ≈ 1 − 2% to the visual flux. We further analyse OGLE photometric data for the presence of eclipses or ellipsoidal variations. Results. Out of the 51 SB1 systems, 43 (84%) are found to have non-degenerate stellar companions, of which 28 are confident detections, and 15 are less certain (SB1: or SB2:). Of these 43 targets, one is found to be a triple (VFTS 64), and two are found to be quadruples (VFTS 120, 702). Our sample includes a total of eight eclipsing binaries. The remaining 8 targets (16%) retain an SB1 classification. We model the mass-ratio distribution as f (q) ∝ q κ , and derive κ through a Bayesian approach. We use massratio constraints from previously known SB2 binaries, newly uncovered SB2 binaries, and SB1 binaries, while accounting for binary detection bias. We find κ = 0.2 ± 0.2 for the entire sample and κ = −0.2 ± 0.2 when excluding binaries with periods shorter than 10 d. In contrast, κ = 1.2 ± 0.5 is retrieved for tight binaries (P < 10 d), proposed here to be a consequence of binary interaction. Aside from the unambiguous O+BH binary VFTS 243, analysed in detail in a separate paper, we identify two additional OB+BH candidates: VFTS 514 and 779. Conclusions. Our study firmly establishes a virtually flat natal mass-ratio distribution (κ = 0) for O-type stars at LMC metallicity, covering the entire mass-ratio range (0.05 < q < 1) and periods in the range 0 < log P < 3 [d]. The nature of the OB+BH candidates should be verified through future monitoring, but the frequency of OB+BH candidates is generally in line with recent predictions at LMC metallicity.

Section: Examples: Vfts 350 (O+o) and Vfts 779 (B+bh?)contrasting

confidence: 53%

The Tarantula Massive Binary Monitoring

Shenar

et al. 2022

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“…We assume that the stars are on a 1.5-day circular orbit, moving anti-phase, and we assume a projected rotation of 50 km s −1 for each. Under these conditions, a double-lined system may appear single if the RV separation between the two profiles is not sufficient for them to be clearly de-blended (Bodensteiner et al 2021;Banyard et al 2022). Our simulations only provides us with a mean spectrum of each inner close system, and not of individual intermediate-mass stars in the inner systems.…”

Section: Detection Limit Considering Triple Systemsmentioning

confidence: 99%

Identifying quiescent compact objects in massive Galactic single-lined spectroscopic binaries

Shenar

et al. 2022

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Context. The quest to detect dormant stellar-mass black holes (BHs) in massive binaries (i.e. OB+BH systems) is challenging; only a few candidates have been claimed to date, all of which must still be confirmed. Aims. To search for these rare objects, we study 32 Galactic O-type stars that were reported as single-lined spectroscopic binaries (SB1s) in the literature. In our sample we include Cyg X-1, which is known to host an accreting stellar-mass BH, and HD 74194, a supergiant fast X-ray transient, in order to validate our methodology. The final goal is to characterise the nature of the unseen companions to determine if they are main-sequence (MS) stars, stripped helium stars, triples, or compact objects such as neutron stars (NSs) or stellar-mass BHs. Methods. After measuring radial velocities and deriving orbital solutions for all the systems in our sample, we performed spectral disentangling to extract putative signatures of faint secondary companions from the composite spectra. We derived stellar parameters for the visible stars and estimated the mass ranges of the secondary stars using the binary mass function. Variability observed in the photometric TESS light curves was also searched for indications of the presence of putative companions, degenerate or not. Results. In 17 of the 32 systems reported as SB1s, we extract secondary signatures, down to mass ratios of ∼ 0.15. For the 17 newly detected double-lined spectroscopic binaries (SB2s), we derive physical properties of the individual components and discuss why they have not been detected as such before. Among the remaining systems, we identify nine systems with possible NS or low-mass MS companions. For Cyg X-1 and HD 130298, we are not able to extract any signatures for the companions, and the minimum masses of their companions are estimated to be about 7 M . Our simulations show that secondaries with such a mass should be detectable from our dataset, no matter their nature: MS stars, stripped helium stars or even triples. While this is expected for Cyg X-1, confirming our methodology, our simulations also strongly suggest that HD 130298 could be another candidate to host a stellar-mass BH. Conclusions. The quest to detect dormant stellar-mass BHs in massive binaries is far from over, and many more systems need to be scrutinised. Our analysis allows us to detect good candidates, but confirming the BH nature of their companions will require further dedicated monitorings, sophisticated analysis techniques, and multi-wavelength observations.

“…4.1. We guide our assumptions on the underlying parent parameter distributions (period, mass ratio, eccentricity) on what was done by Sana et al (2013) and Bodensteiner et al (2021). We use power law representations of these distributions:…”

Section: Sb1 Biasmentioning

confidence: 99%

“…When making assumptions on the values of the indexes π, κ and η, the impact of varying these choices on the calculated overall detection probability should be considered. It was found by Sana et al (2013) and Bodensteiner et al (2021) that the dominant factor impacting the computed detection probability is the shape of the period distribution. For example, choosing π to favour shorter-period systems results in systems that are easier to detect given our detection criteria that relies on the RV amplitude.…”

Section: Sb1 Biasmentioning

confidence: 99%

“…Several spectroscopic (Sana et al 2012(Sana et al , 2013Kobulnicky et al 2014;Almeida et al 2017) and interferometric (Mason et al 2009;Sana et al 2014;Aldoretta et al 2015) studies of large samples of O stars in different environments have constrained the multiplicity fraction and orbital parameter distributions of these stars. Similar constraints are scarcer for B-type stars (Kobulnicky et al 2014;Dunstall et al 2015;Bodensteiner et al 2021;Villaseñor et al 2021). Abt & Levy (1990, in a follow up to Abt & Levy 1978) performed a study of 109 (mostly) field B stars in the Galaxy between spectral types B2 and B5.…”

Section: Introductionmentioning

confidence: 98%

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The observed multiplicity properties of B-type stars in the Galactic young open cluster NGC 6231

Banyard

et al. 2022

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Context. It is well known that massive O stars are frequently (if not always) found in binary or higher-order multiple systems, but this fact has been less robustly investigated for the lower mass range of the massive stars, represented by B-type stars. Obtaining the binary fraction and orbital parameter distributions of B-type stars is crucial to understand the impact of multiplicity on the archetypal progenitor of core-collapse supernovae as well as to properly investigate formation channels for gravitational wave progenitors. Aims. This work aims to characterise the multiplicity of the B star population of the young open cluster NGC 6231 through multi-epoch optical spectroscopy of 80 B-type stars. Methods. We analyse 31 FLAMES/GIRAFFE observations of 80 B-type stars, monitoring their radial velocities (RVs) and performing a least-squares spectral analysis (Lomb-Scargle) to search for periodicity in those stars with statistically significant variability in their RVs. Results. We constrained an observed spectroscopic binary fraction of 33 ± 5% for the B-type stars of NGC 6231, with a first order bias correction giving a true spectroscopic binary fraction of 52 ± 8%. Out of 27 B-type binary candidates, we obtained orbital solutions for 20 systems: 15 single-lined (SB1) and five double-lined spectroscopic binaries (SB2s). We present these orbital solutions and the orbital parameter distributions associated with them. Conclusions. Our results indicate that Galactic B-type stars are less frequently found in binary systems than their more massive O-type counterparts, but their orbital properties generally resemble those of B- and O-type stars in both the Galaxy and Large Magellanic Cloud.