What apsidal motion reveals about the interior of massive binary stars

peer reviewedApart from asteroseismology, the most efficient observational technique allowing to probe the internal structure of a star is the determination of the apsidal motion in close eccentric binary systems. This secular precession of the major axis of the bi-nary orbit depends on the tidal interactions between the two stars. The rate of this motion is directly related to the internal structure of the stars, in particular their inner density profile. Based on radial velocity and light curve measurements made over a long timescale, the rate of apsidal motion can be constrained, together with the fundamental parameters of the stars. Comparing the observationally determined parameters to theoretical models of stellar structure and evolution then constrains the internal structure of the stars. This powerful technique has been known for years, but has been seldom applied - we are reviewing its interest and reveal recent results

New insight into the massive eccentric binary HD 165052: self-consistent orbital solution, apsidal motion, and fundamental parameters

HD165052 is a short-period massive eccentric binary system that undergoes apsidal motion. As the rate of apsidal motion is directly related to the internal structure constants of the binary components, its study allows to get insight into the internal structure of the stars. We use medium- and high-resolution spectroscopic observations of HD165052 to provide constraints on the fundamental properties of the binary system and the evolutionary state of its components. We apply a spectral disentangling code to reconstruct artefact-free spectra of the individual stars and derive the radial velocities (RVs) at the times of the observations. We perform the first analysis of the disentangled spectra with the non-LTE model atmosphere code CMFGEN to determine the stellar properties. We derive the first self-consistent orbital solution of all existing RV data, including those reported in the literature, accounting for apsidal motion. We build, for the very first time, dedicated stellar evolution tracks with the Cl\'es code requesting the theoretical effective temperatures and luminosities to match those obtained from our spectroscopic analysis. The binary system HD165052, consisting of an O6.5V((f)) primary and an O7V((f)) secondary, displays apsidal motion at a rate of (11.30+0.64-0.49)$\deg$yr$^{-1}$. Evolutionary masses are compared to minimum dynamical masses to constrain the orbital inclination. Evolutionary masses Mev,P=24.8$\pm$1.0M$_\odot$ and Mev,S=20.9$\pm$1.0M$_\odot$ and radii Rev,P=7.0+0.5-0.4R$_\odot$ and Rev,S=6.2+0.4-0.3R$_\odot$ are derived, and the inclination is constrained to 22.1$\deg\le i\le 23.3\deg$. Theoretical apsidal motion rates, derived assuming an age of 2.0+/-0.5 Myr for the binary, are in agreement with the observational determination. The agreement with theoretical apsidal motion rates enforces the inferred values of the evolutionary stellar masses and radii.Comment: 17 pages. arXiv admin note: text overlap with arXiv:2205.1120

Underestimation of the tidal force and apsidal motion in close binary systems by the perturbative approach: Comparisons with non-perturbative models

peer reviewedContext. Stellar deformations play a significant role in the dynamical evolution of stars in binary systems, impacting the tidal dissipation and the outcomes of mass transfer processes. The prevalent method for modelling the deformations and tidal interactions of celestial bodies solely relies on the perturbative approach, which assumes that stellar deformations are minor perturbations to the spherical symmetry. An observable consequence of stellar deformations is the apsidal motion in eccentric systems, which has be observationally determined across numerous binary systems. Aims. Our objective is to assert the reliability of the perturbative approach when applied to close and strongly deformed binary systems. Methods. We have developed a non-perturbative 3D modelling method designed to account for high stellar deformations. We focus on comparing the properties of perturbatively deformed stellar models with our 3D models, particularly in terms of apsidal motion. Results. Our research highlights that the perturbative model becomes imprecise and underestimates the tidal force and rate of apsidal motion at a short orbital separation. This discrepancy primarily results from the first-order treatment in the perturbative approach, and cannot be rectified using straightforward mathematical corrections due to the strong non-linearity and numerous parameters of the problem. We have determined that our methodology affects the modelling of approximately 42% of observed binary systems with measured apsidal motion, introducing a discrepancy greater than 2% when the normalised orbital separation verifies qa 1/5a(1a a e2)/R1a ²a 6.5 (q is the mass ratio of the system, a is its semi-major axis, e is its orbital eccentricity and R1 is the radius of the primary star). Conclusions. The perturbative approach underestimates tidal interactions between bodies up to a 40% for close low-mass binaries. All the subsequent modelling is impacted by our findings, in particular, the tidal dissipation is significantly underestimated. As a result, all binary stellar models are imprecise when applied to systems with a low orbital separation, and the outcomes of these models are also affected by these inaccuracies

Phase-resolved XMM-Newton observations of the massive post-RLOF system HD 149404

peer reviewedContext. We investigated the X-ray emission of HD 149404, a 9.81-day period O-star binary in a post-Roche lobe overflow evolutionary stage. X-ray emission of O-star binaries consists of the intrinsic emission of the individual O stars and a putative additional component arising from the wind-wind interaction. Aims. Phase-locked variations in the X-ray spectra can be used to probe the properties of the stellar winds of such systems. Methods. XMM–Newton observations of HD 149404 collected at two conjunction phases and a quadrature phase were analysed. X-ray spectra were extracted and flux variations as a function of orbital phase were inferred. The flux ratios were analysed with models considering various origins for the X-ray emission. Results. The highest and lowest X-ray fluxes are observed at conjunction phases respectively with the primary and secondary star in front. The flux variations are nearly grey with only marginal energy dependence. None of the models accounting for photoelectric absorption by homogeneous stellar winds perfectly reproduces the observed variations. Whilst the overall X-ray luminosity is consistent with a pure intrinsic emission, the best formal agreement with the observed variations is obtained with a model assuming pure windwind collision X-ray emission. Conclusions. The lack of significant energy-dependence of the opacity most likely hints at the presence of optically thick clumps in the winds of HD149404

Probing ligand and cation binding sites in G-quadruplex nucleic acids by mass spectrometry and electron photodetachment dissociation sequencing

International audienceMass spectrometry provides exquisite detail on ligand and cation binding stoichiometries with a DNA target. The next important step is to develop reliable methods to determine the cation and ligand binding sites in each complex separated by the mass spectrometer. To circumvent the caveat of ligand derivatization for cross-linking, which may alter the ligand binding mode, we explored a tandem mass spectrometry (MS/MS) method that does not require ligand derivatization, and is therefore also applicable to localize metal cations. By obtaining more negative charge states for the complexes using supercharging agents, and by creating radical ions by electron photodetachment, oligonucleotide bonds become weaker than the DNA-cation or DNA-ligand noncovalent bonds upon collision-induced dissociation of the radicals. This electron photodetachment (EPD) method allows to locate the binding regions of cations and ligands by top-down sequencing of the oligonucleotide target. The very potent G-quadruplex ligands 360A and PhenDC3 were found to replace a potassium cation and bind close to the central loop of 4-repeat human telomeric sequences

Apsidal Motion in Massive Binaries: CPD-41° 7742, an Extreme Case?

We study the apsidal motion in close eccentric massive binaries. We focus on CPD-41° 7742, located in the very young and rich open cluster NGC 6231. Measuring the rate of apsidal motion in such a binary system gives insight into the internal structure and evolutionary state of the stars composing it. Independent studies of CPD-41° 7742 in the past showed large discrepancies in the longitude of periastron of the orbit, hinting at the presence of apsidal motion (i.e. slow precession of the line of apsides with time). We perform a consistent analysis of all observational data explicitly accounting for the apsidal motion. We make use of the extensive set of spectroscopic and photometric observations of the binary to infer fundamental parameters of the stars and of the binary. The age estimates are in good agreement with estimates obtained for other massive binaries in NGC 6231. This study confirms the need for enhanced mixing inside the stellar evolution models of the most massive stars to reproduce the observational stellar properties. This points toward larger convective cores than usually considered.Apsidal Motion in Massive Binaries: constraining the internal structure of massive star

Apsidal motion in massive eccentric binaries: The case of CPD-41°7742, and HD 152218 revisited

peer reviewedContext. This paper is part of a study of the apsidal motion in close eccentric massive binary systems, which aims to constrain the internal structure of the stars. We focus on the binary CPD-41° 7742 and briefly revisit the case of HD 152218. Aims. Independent studies of CPD-41° 7742 in the past showed large discrepancies in the longitude of periastron of the orbit, hinting at the presence of apsidal motion. We here perform a consistent analysis of all observational data, explicitly accounting for the rate of change of the longitude of periastron. Methods. We make use of the extensive set of spectroscopic and photometric observations of CPD-41° 7742 to infer values for the fundamental parameters of the stars and of the binary. Applying a disentangling method to the spectra allows us to simultaneously derive the radial velocities (RVs) at the times of observation and reconstruct the individual spectra of the stars. The spectra are analysed by means of the CMFGEN model atmosphere code to determine the stellar properties. We determine the apsidal motion rate in two ways: First, we complement our RVs with those reported in the literature, and, second, we use the phase shifts between the primary and secondary eclipses. The light curves are further analysed by means of the Nightfall code to constrain the orbital inclination and, thereby, the stellar masses. Stellar structure and evolution models are then constructed with the Clés code for the two stars with the constraints provided by the observations. Different prescriptions for the mixing inside the stars are adopted in the models. Newly available photometric data of HD 152218 are analysed, and stellar structure and evolution models are built for the system as for CPD-41° 7742. Results. The binary system CPD-41° 7742, made of an O9.5 V primary (M_P = 17.8 ± 0.5 M⊙, R_P = 7.57 ± 0.09 R⊙, Teff,P = 31 800 ± 1000 K, Lbol,P = 5.28+0.67-0.68 × 10^4 L⊙) and a B1–2 V secondary (M_S = 10.0 ± 0.3 M⊙, R_S = 4.29+0.04-0.06 R⊙, Teff,S = 24 098 ± 1000 K, Lbol,S = 5.58+0.93−0.94 × 10^3 L⊙), displays apsidal motion at a rate of (15.38+0.42−0.51)° yr-1 . Initial masses of 18.0 ± 0.5 M⊙ and 9.9 ± 0.3 M⊙ are deduced for the primary and secondary stars, respectively, and the binary’s age is estimated to be 6.8 ± 1.4 Myr. Regarding HD 152218, initial masses of 20.6 ± 1.5 and 15.5 ± 1.1 M⊙ are deduced for the primary and secondary stars, respectively, and the binary’s age of 5.2 ± 0.8 Myr is inferred. Conclusions. Our analysis of the observational data of CPD-41° 7742 that explicitly accounts for the apsidal motion allows us to explain the discrepancy in periastron longitudes pointed out in past studies of this binary system. The age estimates are in good agreement with estimates obtained for other massive binaries in NGC 6231. This study confirms the need for enhanced mixing in the stellar evolution models of the most massive stars to reproduce the observational stellar properties; this points towards larger convective cores than usually considered

Using CHIRON Spectroscopy to Test the Hypothesis of a Precessing Orbit for the WN4 star EZ CMa

The bright WN4 star EZ CMa exhibits a 3.77 day periodicity in photometry, spectroscopy, and polarimetry but the variations in the measurements are not strictly phase-locked, exhibiting changes in reference times, amplitudes, and the shape of the variability happening over times as short as a few weeks. Recently, 137 days of contiguous, variable photometry from BRITE-Constellation was interpreted as caused either by large-scale dense wind structures modulated by rotation, or by a fast-precessing binary having a slightly shorter 3.626 day orbital period and a fast apsidal motion rate of $1315^\circ\,\text{yr}^{-1}$. We aim at testing the latter hypothesis through analysis of spectroscopy and focus on the N\,{\sc v} $\lambda\,4945$ line. We derive an orbital solution for the system and reject the 3.626 day period to represent the variations in the radial velocities of EZ CMa. An orbital solution with an orbital period of 3.77 days was obtained but at the cost of an extremely high and thus improbable apsidal motion rate. Our best orbital solution yields a period of $3.751\pm0.001$\,days with no apsidal motion. We place our results in the context of other variability studies and system properties. While we cannot fully reject the precessing binary model, we find that the corotating interaction region (CIR) hypothesis is better supported by these and other data through qualitative models of CIRs.Comment: accepted to MNRA

Hubble space telescope images of SN 1987A: Evolution of the Ejecta and the Equatorial Ring from 2009 to 2022

Supernova (SN) 1987A offers a unique opportunity to study how a spatially resolved SN evolves into a young SN remnant. We present and analyze Hubble Space Telescope (HST) imaging observations of SN 1987A obtained in 2022 and compare them with HST observations from 2009 to 2021. These observations allow us to follow the evolution of the equatorial ring (ER), the rapidly expanding ejecta, and emission from the center over a wide range in wavelength from 2000 to 11,000 Å. The ER has continued to fade since it reached its maximum ∼8200 days after the explosion. In contrast, the ejecta brightened until day ∼11,000 before their emission levelled off; the west side brightened more than the east side, which we attribute to the stronger X-ray emission by the ER on that side. The asymmetric ejecta expand homologously in all filters, which are dominated by various emission lines from hydrogen, calcium, and iron. From this overall similarity, we infer the ejecta are chemically well mixed on large scales. The exception is the diffuse morphology observed in the UV filters dominated by emission from the Mg ii resonance lines that get scattered before escaping. The 2022 observations do not show any sign of the compact object that was inferred from highly ionized emission near the remnant’s center observed with JWST. We determine an upper limit on the flux from a compact central source in the [O iii] HST image. The nondetection of this line indicates that the S and Ar lines observed with JWST originate from the O free inner Si–S–Ar-rich zone and/or that the observed [O iii] flux is strongly affected by dust scattering

Non-Standard Errors

In statistics, samples are drawn from a population in a data-generating process (DGP). Standard errors measure the uncertainty in estimates of population parameters. In science, evidence is generated to test hypotheses in an evidence-generating process (EGP). We claim that EGP variation across researchers adds uncertainty: Non-standard errors (NSEs). We study NSEs by letting 164 teams test the same hypotheses on the same data. NSEs turn out to be sizable, but smaller for better reproducible or higher rated research. Adding peer-review stages reduces NSEs. We further find that this type of uncertainty is underestimated by participants