ORCID Profile
0000-0001-6656-4130
Current Organisation
KU Leuven
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Publisher: SPIE
Date: 13-12-2020
DOI: 10.1117/12.2560895
Publisher: SPIE
Date: 13-12-2020
DOI: 10.1117/12.2562486
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: 18-09-2020
Abstract: Stars less than eight times the mass of the Sun end their lives as planetary nebulae, structures of ionized gas thrown off by the star and heated by the exposed stellar core. Planetary nebulae are often bipolar in shape or contain complex morphological features such as rings or spirals. Decin et al. observed the stellar winds of 14 stars during their asymptotic giant branch (AGB) phase of stellar evolution, which immediately precedes the planetary nebula phase. They found morphologies in the AGB winds similar to planetary nebulae and demonstrated that they are produced by the influence of a binary companion on the AGB wind. Science , this issue p. 1497
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: EDP Sciences
Date: 02-2023
DOI: 10.1051/0004-6361/202244808
Abstract: Context. Unambiguous ex les of the influence of tides on self-excited, free stellar pulsations have recently been observationally detected in space-based photometric data. Aims. We aim to investigate U Gru and contextualise it within the growing class of tidally influenced pulsators. An initial analysis of U Gru revealed frequencies spaced by the orbital frequency that are difficult to explain by currently proposed tidal mechanisms. Methods. We reinvestigate the TESS photometry for U Gru alongside new UVES spectroscopy. We analyse the UVES spectroscopy with least-squares deconvolution and spectral disentangling techniques, and perform an atmospheric analysis. We remove the binary signature from the light curve using an effective model in order to investigate the pulsation signal in the residuals. We track the litudes and phases of the residual pulsations as a function of the orbital period to reveal their tidal influence. Results. We establish that U Gru is likely a hierarchical triple system. We identify a single p -mode oscillation that exhibits litude and phase variation over the binary orbit. We propose a toy model to demonstrate that the series of frequencies separated by the orbital frequency can be reproduced by eclipse mapping. We find no evidence of modulation to the other independent oscillation modes. Conclusions. We demonstrate that U Gru hosts at least one tidally perturbed pulsation. Additionally, we argue that eclipse mapping of the dominant, tidally perturbed mode can produce the series of frequencies separated by the observed orbital frequency. Our simulations show that the effects of eclipse mapping are mode dependent, and are not expected to produce an observable signature for all pulsation modes in an eclipsing binary.
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.
Publisher: EDP Sciences
Date: 02-2022
DOI: 10.1051/0004-6361/202142375
Abstract: Context. There is currently a niche for providing high-cadence, high resolution, time-series optical spectroscopy from space, which can be filled by using a low-cost cubesat mission. The Belgian-led ESA/KU Leuven CubeSpec mission is specifically designed to provide space-based, low-cost spectroscopy with specific capabilities that can be optimised for a particular science need. Approved as an ESA in-orbit demonstrator, the CubeSpec satellite’s primary science objective will be to focus on obtaining high-cadence, high resolution optical spectroscopic data to facilitate asteroseismology of pulsating massive stars. Aims. In this first paper, we aim to search for pulsating massive stars suitable for the CubeSpec mission, specifically β Cep stars, which typically require time-series spectroscopy to identify the geometry of their pulsation modes. Methods. Based on the science requirements needed to enable asteroseismology of massive stars with the capabilities of CubeSpec’s spectrograph, we combined a literature study for pulsation with the analysis of recent high-cadence time-series photometry from the Transiting Exoplanet Survey Satellite (TESS) mission to classify the variability for stars brighter than V ≤ 4 mag and between O9 and B3 in spectral type. Results. Among the 90 stars that meet our magnitude and spectral type requirements, we identified 23 promising β Cep stars with high- litude (non-)radial pulsation modes with frequencies below 7 d −1 . Using further constraints on projected rotational velocities, pulsation litudes, and the number of pulsation modes, we devised a prioritised target list for the CubeSpec mission according to its science requirements and the potential of the targets for asteroseismology. The full target catalogue further provides a modern TESS-based review of line profile and photometric variability properties among bright O9–B3 stars.
Location: United States of America
Location: Netherlands
No related grants have been discovered for Hugues Sana.