The Tarantula massive binary monitoring: VI. Characterisation of hidden companions in 51 single-lined O-type binaries : a flat mass-ratio distribution and black-hole binary candidates
<i>Context.<i/> 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 ob...
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| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
23. September 2022
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| In: |
Astronomy and astrophysics
Year: 2022, Volume: 665, Pages: 1-42 |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202244245 |
| Online Access: | Verlag, kostenfrei, Volltext: https://doi.org/10.1051/0004-6361/202244245 Verlag, kostenfrei, Volltext: https://www.aanda.org/articles/aa/abs/2022/09/aa44245-22/aa44245-22.html 
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| Author Notes: | T. Shenar, H. Sana, L. Mahy, J. Maíz Apellániz, Paul A. Crowther, M. Gromadzki, A. Herrero, N. Langer, P. Marchant, F.R.N. Schneider, K. Sen, I. Soszyński, and S. Toonen |
| Summary: | <i>Context.<i/> 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 they are thus valuable for establishing the natal mass ratio distribution of massive stars.<i>Aims.<i/> 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 a few days to years (0 < log <i>P <<i/> 3 [d]). Our goals are to hunt for BHs and sample the low-mass end of the mass-ratio distribution.<i>Methods.<i/> To uncover the hidden companions, we implemented the shift-and-add grid disentangling algorithm using 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 analysed OGLE photometric data for the presence of eclipses or ellipsoidal variations.<i>Results.<i/> 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 eight targets (16%) retain an SB1 classification. We modelled the mass-ratio distribution as <i>f<i/> (<i>q<i/>) ∝ <i>q<i/><sup><i>κ<i/><sup/>, and derived k through a Bayesian approach. We used massratio constraints from previously known SB2 binaries, newly uncovered SB2 binaries, and SB1 binaries, while accounting for binary detection bias. We found <i>k<i/> = 0.2 ± 0.2 for the entire sample and <i>κ<i/> = −0.2 ± 0.2 when excluding binaries with periods shorter than 10 d. In contrast, <i>k<i/> = 1.2 ± 0.5 was retrieved for tight binaries (<i>P<i/> < 10 d), and it is proposed here to be a consequence of binary interactions. Aside from the unambiguous O+BH binary VFTS 243, which was analysed in detail in a separate paper, we identified two additional OB+BH candidates: VFTS 514 and 779.<i>Conclusions.<i/> Our study firmly establishes a virtually flat natal mass-ratio distribution (<i>κ<i/> = 0) for O-type stars at LMC metallicity, covering the entire mass-ratio range (0.05 < <i>q<i/> < 1) and periods in the range 0 < log <i>P<i/> < 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. |
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| Item Description: | Gesehen am 07.12.2022 |
| Physical Description: | Online Resource |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202244245 |