ORCID Profile
0000-0003-0642-8107
Current Organisations
KU Leuven
,
Tel Aviv University
,
University of Amsterdam
,
Centro de Astrobiología
,
University of Potsdam
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Publisher: Oxford University Press (OUP)
Date: 18-09-2023
Publisher: EDP Sciences
Date: 08-2022
DOI: 10.1051/0004-6361/202243147
Abstract: 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 s le 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 s le, 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 in idual 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.
Publisher: EDP Sciences
Date: 06-2021
DOI: 10.1051/0004-6361/202140693
Abstract: Context. The evolution of the most massive stars and their upper-mass limit remain insufficiently constrained. Very massive stars are characterized by powerful winds and spectroscopically appear as hydrogen-rich Wolf–Rayet (WR) stars on the main sequence. R 144 is the visually brightest WR star in the Large Magellanic Cloud. R 144 was reported to be a binary, making it potentially the most massive binary observed yet. However, the orbit and properties of R 144 have yet to be established. Aims. Our aim is to derive the physical, atmospheric, and orbital parameters of R 144 and to interpret its evolutionary status. Methods. We performed a comprehensive spectral, photometric, orbital, and polarimetric analysis of R 144. We measured radial velocities via cross-correlation. Spectral disentangling was performed using the shift-and-add technique. We used the Potsdam Wolf–Rayet code for the spectral analysis. We further present X-ray and optical light curves of R 144, and we analyse the latter using a hybrid model combining wind eclipses and colliding winds to constrain the orbital inclination i . Results. R 144 is an eccentric ( e = 0.51) 74.2−d binary comprising two relatively evolved (age ≈2 Myr), H-rich WR stars (surface mass fraction X H ≈ 0.4). The hotter primary (WN5/6h, T * = 50 kK) and the cooler secondary (WN6/7h, T * = 45 kK) have nearly equal masses of M sin 3 i = 48.3 ± 1.8 M ⊙ and 45.5 ± 1.9 M ⊙ , respectively. The combination of low rotation and H depletion observed in the system is reproduced well by contemporary evolution models that include boosted mass loss at the upper-mass end. The systemic velocity of R 144 and its relative isolation suggest that this binary was ejected as a runaway from the neighbouring R 136 cluster. The optical light curve shows a clear orbital modulation that can be explained as a combination of two processes: excess emission stemming from wind-wind collisions and double wind eclipses. Our light-curve model implies an orbital inclination of i = 60.4 ± 1.5°, resulting in accurately constrained dynamical masses of M 1,dyn = 74 ± 4 M ⊙ and M 2,dyn = 69 ± 4 M ⊙ . Assuming that both binary components are core H-burning, these masses are difficult to reconcile with the derived luminosities (log L 1,2 ∕ L ⊙ = 6.44, 6.39), which correspond to evolutionary masses of the order of M 1, ev ≈ 110 M ⊙ and M 2, ev ≈ 100 M ⊙ . Taken at face value, our results imply that both stars have high classical Eddington factors of Γ e = 0.78 ± 0.10. If the stars are on the main sequence, their derived radii ( R * ≈ 25 R ⊙ ) suggest that they are only slightly inflated, even at this high Eddington factor. Alternatively, the stars could be core He-burning, strongly inflated from the regular size of classical WR stars (≈ 1 R ⊙ ) this scenario could help resolve the observed mass discrepancy. Conclusions. R144 is one of the few very massive extragalactic binaries ever weighed without the usage of evolution models, but poses several challenges in terms of the measured masses of its components. To advance, we strongly advocate for future polarimetric, photometric, and spectroscopic monitoring of R 144 and other very massive binaries.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-08-2023
Abstract: Magnetars are highly magnetized neutron stars, the formation mechanism of which is unknown. Hot helium-rich stars with spectra dominated by emission lines are known as Wolf-Rayet stars. We observed the binary system HD 45166 using spectropolarimetry and reanalyzed its orbit using archival data. We found that the system contains a Wolf-Rayet star with a mass of 2 solar masses and a magnetic field of 43 kilogauss. Stellar evolution calculations indicate that this component will explode as a supernova, and that its magnetic field is strong enough for the supernova to leave a magnetar remnant. We propose that the magnetized Wolf-Rayet star formed by the merger of two lower-mass helium stars.
Publisher: American Astronomical Society
Date: 19-08-2015
Publisher: Oxford University Press (OUP)
Date: 30-05-2022
Abstract: We present the analysis of the optical variability of the early, nitrogen-rich Wolf–Rayet (WR) star WR 7. The analysis of multisector Transiting Exoplanet Survey Satellite (TESS) light curves and high-resolution spectroscopic observations confirm multiperiodic variability that is modulated on time-scales of years. We detect a dominant period of 2.6433 ± 0.0005 d in the TESS sectors 33 and 34 light curves in addition to the previously reported high-frequency features from sector 7. We discuss the plausible mechanisms that may be responsible for such variability in WR 7, including pulsations, binarity, co-rotating interaction regions (CIRs), and clumpy winds. Given the lack of strong evidence for the presence of a stellar or compact companion, we suggest that WR 7 may pulsate in quasi-coherent modes in addition to wind variability likely caused by CIRs on top of stochastic low-frequency variability. WR 7 is certainly a worthy target for future monitoring in both spectroscopy and photometry to s le both the short (≲1 d) and long (≳1000 d) variability time-scales.
Publisher: Oxford University Press (OUP)
Date: 14-03-2023
Abstract: A black hole candidate orbiting a luminous star in the Large Magellanic Cloud young cluster NGC 1850 (∼100 Myr) has recently been reported based on radial velocity and light-curve modelling. Subsequently, an alternative explanation has been suggested for the system: a bloated post-mass transfer secondary star (Minitial ∼ 4–5 M⊙ and Mcurrent ∼ 1–2 M⊙) with a more massive, yet luminous companion (the primary). Upon reanalysis of the MUSE spectra, we found that the radial velocity variations originally reported were underestimated (K2, revised = 176 ± 3 km s−1 versus K2, original = 140 ± 3 km s−1) because of the weighting scheme adopted in the full-spectrum fitting analysis. The increased radial velocity semi- litude translates into a system mass function larger than previously deduced (frevised = 2.83 M⊙versus foriginal = 1.42 M⊙). By exploiting the spectral disentangling technique, we place an upper limit of 10 per cent of a luminous primary source to the observed optical light in NGC1850 BH1, assuming that the primary and secondary are the only components contributing to the system. Furthermore, by analysing archival near-infrared data, we find clues to the presence of an accretion disc in the system. These constraints support a low-mass post-mass transfer star but do not provide a definitive answer whether the unseen component in NGC1850 BH1 is indeed a black hole. These results predict a scenario where, if a primary luminous source of mass M ≥ 4.7 M⊙ is present in the system (given the inclination and secondary mass constraints), it must be hidden in a optically thick disc to be undetected in the MUSE spectra.
No related grants have been discovered for Tomer Shenar.