Astronomy and Astrophysics, volume 665A, 148-148 (2022/9-1)
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.
SHENAR T., SANA H., MAHY L., MAIZ APELLANIZ J., CROWTHER P.A., GROMADZKI M., HERRERO A., LANGER N., MARCHANT P., SCHNEIDER F.R.N., SEN K., SOSZYNSKI I. and TOONEN S.
Abstract (from CDS):
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 they 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 a few days to years (0 < log P < 3 [d]). Our goals are to hunt for BHs and sample the low-mass end of the mass-ratio distribution.
Methods. 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.
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 eight targets (16%) retain an SB1 classification. We modelled the mass-ratio distribution as f (q) ∝ qκ, and derivedK 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 foundK = 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,K = 1.2 ± 0.5 was retrieved for tight binaries (P < 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.
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.
© T. Shenar et al. 2022
binaries: spectroscopic - stars: black holes - Magellanic Clouds - stars: massive - stars: evolution
VizieR on-line data:
<Available at CDS (J/A+A/665/A148): table1.dat table2.dat tabled1.dat list.dat sp/*>
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