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Recent gravitational wave (GW) observations include possible detections of black hole—neutron star binary mergers. As with binary black hole mergers, numerical simulations help characterize the sources. For binary systems with neutron star components, the simulations help to predict the imprint of tidal deformations and disruptions on the GW signals. In a previous study, we investigated how the mass of the black hole has an impact on the disruption of the neutron star and, as a consequence, on the shape of the GWs emitted. We extend these results to study the effects of varying the compactness of the neutron star. We consider neutron star compactness in the 0.113–0.2 range for binaries with mass ratios of 3 and 5. As the compactness and the mass ratio increase, the binary system behaves during the late inspiral and merger more like a black hole binary. For the cases with the least compact neutron star, the GWs emitted, in terms of mismatches, are the most distinguishable from those by a binary black hole. The disruption of the star significantly suppresses the kicks on the final black hole. The disruption also affects, although not dramatically, the spin of the final black hole. Lastly, for neutron stars with low compactness, the quasi-normal ringing of the black hole after the merger does not show a clean quasi-normal ringing because of the late accretion of debris from the neutron star. [ABSTRACT FROM AUTHOR]

We present the results obtained from X-ray and optical analysis of the Be/X-ray binary IGR J06074+2205, focusing on before, during, and after the X-ray outbursts in 2023 October and December. The properties of the neutron star in the binary are investigated using NICER and NuSTAR observations during the X-ray outbursts. The pulse profiles across a broad energy range, are found to be strongly dependent on luminosity and energy, revealing the complex nature of the emitting region. An absorbed power law can describe each NICER spectrum in the 1–7 keV band. The 3–79 keV NuSTAR spectrum can be well described by a negative and positive power law with an exponential cut-off model. Utilizing the MAXI/GSC long-term light curve, we estimate the probable orbital period to be 80 or 80/n (n = 2, 3, 4) d. We investigate the evolution of the circumstellar disc around the Be star by using optical spectroscopic observations of the system between 2022 and 2024. We observe variable H  |$\alpha$| and Fe  ii emission lines with an increase in equivalent width, indicating the presence of a dynamic circumstellar disc. A distinct variation in the V/R value for H  |$\alpha$| and Fe  ii lines is also observed. The appearance of additional emission lines, such as He  i (5875.72 Å), He  i (6678 Å), and He  i (7065 Å), during the post-outburst observation in 2024 February suggests the growing of a larger or denser circumstellar disc. The disc continues to grow without any noticeable mass-loss, even during the 2023 X-ray outbursts, which may lead to a future giant X-ray outburst. [ABSTRACT FROM AUTHOR]

Two decades of extensive spectroscopic monitoring of WR 104 is used to confront what we think we understand about this iconic prototype of the dust-producing pinwheel stars. Convincing SB1 orbital solutions are obtained for both the WC9d star and its OB companion. The period (⁠|$241.54 \pm 0.14$| d) and circular orbit agree perfectly with results from modelling images of the rotating dust spiral. Contrary to those results though, the orbit is found to be significantly inclined instead of face-on. The two SB1 solutions each indicate |$i \sim 45^{\circ }$| but could be as low as |$\sim 34^{\circ }$|⁠. This result naturally provides an explanation for the long puzzling photometric and emission line strength variations but is difficult to reconcile with the imaging. Confirmation that colliding winds are present is found by the detection of variable excess emission in two of the lines where it would be most expected. The changing shapes of this excess emission are not perfectly phase-locked though, which will complicate future modelling. [ABSTRACT FROM AUTHOR]

The coalescence of binary neutron stars (BNS) is a prolific source of gravitational waves (GWs) and electromagnetic (EM) radiation, offering a dual observational window into the Universe. Lowering the signal-to-noise ratio (S/N) threshold is a simple and cost-effective way to enhance the detection probability of GWs from BNS mergers. In this study, we introduce a metric of the purity of joint GW and EM detections |$P_{\rm joint}$|⁠ , which is in analogue to |$P_{\rm astro}$| in GW-only observations. By simulating BNS merger GWs jointly detected by the Handford, LIGO Livingston, and Virgo network and EM counterparts (kilonovae and short gamma-ray bursts, sGRBs) with an assumed merger rate density of BNS, we generate catalogues of GW events and EM counterparts. Through this simulation, we analyse joint detection pairs, both correct and misidentified. We find the following: (1) For kilonovae, requiring |$P_{\rm joint}\gt $| 95 per cent instead of |$P_{\rm astro}\gt 95~{{\ \rm per\ cent}}$| reduces the S/N from 9.2 to 8.5–8.8, allowing 5–13 additional joint detections per year and increasing the GW detection volume by 9–17 per cent. (2) For sGRBs, requiring |$P_{\rm joint}\gt $| 95 per cent instead of |$P_{\rm astro}$| reduces the S/N from 9.2 to 8.1–8.5. (3) Increasing kilonova or sGRB detection capability does not improve |$P_{\rm joint}$| due to a higher rate of misidentifications. We also show that sub-threshold GW and kilonova detections can reduce the uncertainty in measuring the Hubble constant to 89–92 per cent of its original value, and sub-threshold GW and sGRB observations can enhance the precision of constraining the speed of GWs to 88 per cent of previously established values. [ABSTRACT FROM AUTHOR]

Galactic white dwarf binaries (WDBs) and black hole binaries (BHBs) will be gravitational wave (GW) sources for LISA. Their detection will provide insights into binary evolution and the evolution of our Galaxy through cosmic history. Here, we make predictions of the expected WDB and BHB population within our Galaxy. We combine predictions of the compact remnant binary populations expected by stellar evolution from the detailed Binary Population and Spectral Synthesis (BPASS) code, with a Milky Way analogue galaxy model from the Feedback in Realistic Environment (FIRE) simulations. We use PhenomA and legwork to simulate LISA observations. Both packages make similar predictions that on average four Galactic BHBs and 673 Galactic WDBs are above the signal-to-noise ratio (SNR) threshold of 7 after a four-year mission. We compare these predictions to earlier results using the binary star evolution (BSE) code with the same FIRE model galaxy. We find that BPASS predicts a few more LISA observable Galactic BHBs and a twentieth of the Galactic WDBs. The differences are due to the different physical assumptions that have gone into the binary evolution calculations. These results indicate that the expected population of compact binaries that LISA will detect depends very sensitively on the binary population synthesis models used and thus observations of the LISA population will provide tight constraints on our modelling of binary stars. Finally, from our synthetic populations, we have created mock LISA signals that can be used to test and refine data processing methods of the eventual LISA observations. [ABSTRACT FROM AUTHOR]

Chae’s analyses on GAIA observations of wide binary stars have fortified the paradigm of extended gravity with particular attention to MOND-like theories. We recall that, starting from the origin of Einstein’s general relativity, the request of Mach on the structure of the theory has been the core of the foundational debate. This issue is strictly connected with the nature of the mass–energy equivalence. This was exactly the key point that Einstein used to derive the same general relativity. On the other hand, the current requirements of particle physics and the open questions within extended gravity theories, which have recently been further strengthened by the analyses of GAIA observations, request a better understanding of the Equivalence Principle. By considering a direct coupling between the Ricci curvature scalar and the matter Lagrangian, a nongeodesic ratio between the inertial and gravitational masses can be fixed and MOND-like theories are retrieved at low energies. [ABSTRACT FROM AUTHOR]

We present in this paper an analysis of near-infrared observations of the 0.3- |${\rm M}_{\odot }$| protostar V347 Aurigae (V347 Aur) collected with the SPIRou high-resolution spectropolarimeter and velocimeter at the 3.6-m Canada-France-Hawaii Telescope from 2019 October to 2023 April. From a set of 79 unpolarized and circularly polarized spectra of V347 Aur to which we applied Least-Squares Deconvolution (LSD), we derived radial velocities and longitudinal fields, along with their temporal variations over our monitoring campaign of 1258 d. Our data show that V347 Aur is an eccentric binary system with an orbital period of |$154.6\pm 0.7$| d, experiencing strong-to-extreme accretion events near periastron. The companion is a |$29.0\pm 1.6$| |${\rm M}_{{2\!\!_{\mathbf +}}}$| brown dwarf, a rare member of the brown dwarf desert of close companions around M dwarfs. We detect weak longitudinal fields (⁠|$\lt $| 100 G) at the surface of V347 Aur, significantly weaker than those of more evolved prototypical T Tauri stars. These fields show small-amplitude rotational modulation, indicating a mainly axisymmetric parent large-scale magnetic topology, and larger fluctuations at half the orbital period, suggesting that what we dub a 'pulsed dynamo' triggered by orbital motion and pulsed accretion operates in V347 Aur. Applying Zeeman–Doppler imaging to our circularly polarized LSD profiles, we find that the large-scale field of V347 Aur is mainly toroidal for most of our observations, with the toroidal component switching sign near periastron and apoastron. The weak large-scale dipole (⁠|$\simeq 30$| G) is not able to disrupt the disc beyond 1.3 |$R_{\star }$| even at the lowest accretion rates, implying longitudinally distributed (rather than localized) accretion at the surface of the protostar. [ABSTRACT FROM AUTHOR]

The Wide Angle Search for Planets (WASP) survey used transit photometry to discover nearly 200 gas-giant exoplanets and derive their planetary and stellar parameters. Reliable determination of the planetary density depends on accurate measurement of the planet's radius, obtained from the transit depth and photodynamical determination of the stellar radius. The stellar density and hence the stellar radius are typically determined in a model-independent way from the star's reflex orbital acceleration and the transit profile. Additional flux coming from the system due to a bright, undetected stellar binary companion can, however, potentially dilute the transit curve and radial velocity signal, leading to underestimation of the planet's mass and radius, and to overestimation of the planet's density. In this study, we cross-check the published radii of all the WASP planet-host stars, determined from their transit profiles and radial velocity curves, against radiometric measurements of stellar radii derived from their angular diameters (via the infrared flux method) and trigonometric parallaxes. We identify eight systems showing radiometric stellar radii significantly greater than their published photodynamical values: WASPs 20, 85, 86, 103, 105, 129, 144, and 171. We investigate these systems in more detail to establish plausible ranges of angular and radial velocity separations within which such 'stealth binaries' could evade detection, and deduce their likely orbital periods, mass ratios, and flux ratios. After accounting for the dilution of transit depth and radial velocity amplitude, we find that, on average, the planetary densities for the identified stealth binary systems should be reduced by a factor of 1.3. [ABSTRACT FROM AUTHOR]

With advancements in gravitational wave detection technology, an increasing number of binary neutron star (BNS) merger events are expected to be detected. Due to the narrow opening angle of jet cores, many BNS merger events occur off-axis, resulting in numerous gamma-ray bursts (GRBs) going undetected. Models suggest that kilonovae, which can be observed off-axis, offer more opportunities to be detected in the optical/near-infrared band as electromagnetic counterparts of BNS merger events. In this study, we calculate kilonova emission using a three-dimensional semi-analytical code and model the GRB afterglow emission with the open-source Python package afterglowpy at various inclination angles. Our results show that it is possible to identify the kilonova signal from the observed color evolution of BNS merger events. We also deduce the optimal observing window for SVOM/VT and JWST/NIRCam, which depends on the viewing angle, jet opening angle, and circumburst density. These parameters can be cross-checked with the multi-band afterglow fitting. We suggest that kilonovae are more likely to be identified at larger inclination angles, which can also help determine whether the observed signals without accompanying GRBs originate from BNS mergers. [ABSTRACT FROM AUTHOR]

We present the Transiting Exoplanet Survey Satellite (TESS) light curve analysis of HX Velorum, located in the Southern Hemisphere, where one of the components is found for the first time to be a β$$ \beta $$ Cep (BCEP) type pulsator. The TESS observations of HX Velorum were published in a total of 6 sectors. Fourier analysis of the observations reveals that the frequencies can be divided into two categories, one of which is related to the orbital period and the other related to the β$$ \beta $$ Cep‐type pulsation. Its non‐eclipsing light curve was analyzed with the well‐known Wilson–Devinney code, and we obtained the geometric and physical parameters of the components using published radial velocity and light curve data by making some assumptions. We obtained plausible masses and radii of the primary and secondary components as M1=9.48±0.27M⊙$$ {M}_1=9.48\pm 0.27{M}_{\odot } $$, M2=5.92±0.17M⊙$$ {M}_2=5.92\pm 0.17{M}_{\odot } $$ and R1=3.93±0.04R⊙$$ {R}_1=3.93\pm 0.04{R}_{\odot } $$, R2=3.59±0.03R⊙$$ {R}_2=3.59\pm 0.03{R}_{\odot } $$, respectively. The obtained system's distance of ∼400$$ \sim 400 $$ pc is smaller than the Gaia distances found in the literature. [ABSTRACT FROM AUTHOR]

Gaia Data Release 3 (DR3) provides the first classifications for the sources in Gaia 's all-sky database. Most Gaia sources are stars in the Milky Way, but DR3 also contains many sources that belong to nearby galaxies, as well as background galaxies and quasars. In this work, we compare the Gaia classifications from the Discrete Source Classifier (CU8-DSC) module to the more detailed and heterogeneous classifications in NED (NASA Extragalactic Database) and/or SIMBAD (Set of Identifications, Measurements and Bibliography for Astronomical Data) for sources with sky positions within twice the Holmberg radius of nearby galaxies. Matching these catalogues gives approximately |$3.2\times 10^5$| unique Gaia matches for |$4\times 10^5$| sources over 1040 galaxies (excluding some large Local Group galaxies) in the Local Volume Galaxy catalogue. Matched sources contain a lower fraction of Gaia -classified stars and higher fractions of galaxies and quasars (⁠|$\sim 95$| per cent, 2 per cent, and 2 per cent, respectively) than DR3 overall. Considering NED (SIMBAD) classifications as truth values, the balanced accuracy of Gaia classification is 0.80 (0.83): the most common disagreements are literature-classified galaxies Gaia -classified as stars and literature-classified stars Gaia -classified as quasars. Purity (P) and completeness (C) metrics show that agreement between Gaia classification and NED/SIMBAD classification is best for stars (⁠|$P\, \mathrm{ and}\, C\sim 0.9$|⁠), and decreases for quasars (⁠|$P\lt 0.3$| and |$0.7\lt C\lt 0.8$|⁠), galaxies (⁠|$0.7\lt P\lt 0.8$| and |$0.3\lt C\lt 0.6$|⁠), white dwarfs (⁠|$0.04\lt P\lt 0.6$| and |$C\sim 0.6$|⁠), and binary stars (⁠|$P\, \mathrm{ and}\, C\lt 0.1$|⁠). NED or SIMBAD sources classified only by detection wavelength are most often Gaia -classified as stars, while non-stellar components of galaxies appear in all Gaia classes. [ABSTRACT FROM AUTHOR]

It has been generally accepted that the originators of the double star astronomy were Christian Mayer and William Herschel. We recovered the memory of the poorly known Italian astronomer Giovanni Battista Hodierna, who published the first catalogue of stellar binaries over a century before Mayer and Herschel. We analysed the fourth section of 1654 G. B. Hodierna's book ' De systemate orbis cometici deque admirandis coeli characteribus '. There, Hodierna listed a dozen pairs of stars whose identification with modern star names had been lost for centuries. To identify the pairs, we used Hodierna's Latin descriptions of location in constellations for all primary stars, ecliptic coordinates and angular separations to companions for some, and the Washington Double Star, Hipparcos , and Gaia catalogues. We were able to identify the twelve primaries and eleven multiple systems with companions, of which nine were double and two were triple. Besides, with up-to-date data, we confirmed that four systems are physically bound: Atlas and Pleione, |$\alpha ^{1,2}$| Lib, |$\nu ^{1,2}$| Dra, and |$\theta ^{1}$| Ori A, C, and D. The other seven pairs are alignments of very bright stars at different distances. [ABSTRACT FROM AUTHOR]

The viscous decretion disc (VDD) scenario has been used to model the observables of the Be stars. Its capability to predict individual observables has been confirmed for several Be stars. Here, we simultaneously analyse the spectroscopic and |$BVI$| -band photometric data for the Be star MT91-213 with the Monte Carlo radiative-transfer code hdust to determine the stellar parameters, geometry, and physical conditions for its circumstellar disc. MT91-213 is the primary component of a binary system whose companion is the pulsar PSR J2032+4127. We find that the VDD model can simultaneously reproduce the multiple observables qualitatively, but not quantitatively. We determine the mass of the primary star to be 13.1  |${\rm M}_{\odot }$| which is smaller than reported in the literature. We present a dynamical scenario for the evolving disc density from a diffuse to a dense phase. Also, we determine that the inclination of the disc is about 40 |$^{\circ }$| which means it is 20 |$^{\circ }$| tilted from the orbit of the secondary star. Our results indicate that the mass loss rate for MT91-213 is |$\sim 10^{-7}$| to |$10^{-6} {\rm M}_{\odot }\,\mathrm{yr}^{-1}$| which is in agreement with the suggested values in the literature, required to explain the observed X-ray synchrotron luminosity, |$L_\mathrm{x}$|⁠ , for PSR J2032+4127. [ABSTRACT FROM AUTHOR]

Hypervelocity stars (HVSs) are stars which have been ejected from the Galactic Centre (GC) at velocities of up to a few thousand |$\text{km}\, \text{s}^{-1}$|⁠. They are tracers of the Galactic potential and can be used to infer properties of the GC, such as the initial mass function and assembly history. HVSs are rare, however, with only about a dozen promising candidates discovered so far. In this work, we make use of a novel, highly efficient method to identify new HVS candidates in Gaia. This method uses the nearly radial trajectories of HVSs to infer their distances and velocities based on their position and Gaia proper motion alone. Through comparison of inferred distances with Gaia parallaxes and photometry, we identified 600 HVS candidates with G < 20 including the previously discovered S5-HVS1, out of which we obtained ground-based follow-up observations for 196 stars. As we found no new HVSs based on their radial velocity, we used detailed HVS ejection simulations to significantly improve previous HVS ejection rate constraints. In particular, the ejection rate of HVSs more massive than 1 |$\mathrm{M_\odot }$| cannot be higher than |$10^{-5}$| yr |$^{-1}$| at |$2\sigma$| significance. Additionally, we predict that there are 5–45 unbound HVSs in the complete Gaia catalogue (⁠|$1\sigma$| interval), most of which will be main-sequence stars of a few M |$_\odot$| at heliocentric distances of tens to hundreds of kpc. By comparing our results to literature HVS candidates, we find an indication of either a time-dependent ejection rate of HVSs or a non-GC origin of previously identified HVS candidates. [ABSTRACT FROM AUTHOR]

Context. Magnetic wind braking drives the spin-down of low-mass stars and the evolution of most interacting binary stars. A magnetic braking prescription that was claimed to reproduce both the period distribution of cataclysmic variables (CVs) and the evolution of the rotation rates of low-mass stars is based on a relation between the angular momentum loss rate and magnetic field complexity. Aims. The magnetic braking model based on field complexity has been claimed to predict a detached phase that could explain the observed period gap in the period distribution of CVs but has never been tested in detailed models of CV evolution. Here we fill this gap. Methods. We incorporated the suggested magnetic braking law in MESA and simulated the evolution of CVs for different initial stellar masses and initial orbital periods. Results. We find that the prescription for magnetic braking based on field complexity fails to reproduce observations of CVs. The predicted secondary star radii are smaller than measured, and an extended detached phase that is required to explain the observed period gap (a dearth of non-magnetic CVs with periods between ∼2 and ∼3 hours) is not predicted. Conclusions. Proposed magnetic braking prescriptions based on a relation between the angular momentum loss rate and field complexity are too weak to reproduce the bloating of donor stars in CVs derived from observations and, in contrast to previous claims, do not provide an explanation for the observed period gap. The suggested steep decrease in the angular momentum loss rate does not lead to detachment. Stronger magnetic braking prescriptions and a discontinuity at the fully convective boundary are needed to explain the evolution of close binary stars that contain compact objects. The tension between braking laws derived from the spin-down of single stars and those required to explain CVs and other close binaries containing compact objects remains. [ABSTRACT FROM AUTHOR]

Context. Most known spectroscopic binaries are detected through the variation in the radial velocity of the primary star, while the spectral features of the secondary companion remain hidden in the noise. Aims. We present a novel technique for the spectroscopic detection of low-luminosity secondary companions of binary stars. The main goal is to estimate the mass ratio even when the radial velocity of the secondary cannot be measured in individual spectra. Methods. The method aims to bring together all the spectral information of the secondary component into one single feature. In a first step, a spectral disentangling technique is used in an automatic way for a grid of possible values of the mass ratio. Then, the resulting series of secondary component spectra are compared with a grid of synthetic templates with a technique inspired by spectral cross-correlations. By optimizing a function indicative of the significance of the secondary detection, the mass ratio and an estimate of effective temperature are derived. Results. We apply our method to different types of objects and observational datasets: three single-lined spectroscopic binaries in the open cluster Blanco 1 observed at mid-spectral resolution, an early-type binary in the open cluster NGC 2362, and PX Vir, an F-type binary observed at high resolution for which the secondary companion had been detected in the infrared but not in the optical spectral range. It is shown that from standard-quality spectral datasets it is possible to detect the secondary star in systems in which the secondary contributes less than 0.5–1.0% of the total flux. [ABSTRACT FROM AUTHOR]

Context. High-precision and high-cadence photometric surveys such as Kepler or TESS are making huge progress not only in the detection of new extrasolar planets but also in the study of a great number of variable stars. This is the case for central stars of planetary nebulae (PNe), which have similarly benefited from the capabilities of these missions, increasing the number of known binary central stars and helping us to constrain the relationship between binarity and the complex morphologies of their host PNe. Aims. In this paper, we analyse the TESS light curves of a large sample of central stars of PNe with the aim of detecting signs of variability that may hint at the presence of short-period binary nuclei. This will have important implications in understanding PN formation evolution as well as the common envelope phase. Methods. We analysed 62 central stars of true, likely, or possible PNe and modelled the detected variability through an MCMC approach accounting for three effects: reflection, ellipsoidal modulations due to tidal forces, and the so-called Doppler beaming. Among the 62 central stars, only 38 are amenable for this study. The remaining 24 show large contamination from nearby sources preventing an optimal analysis. Also, eight targets are already known binary central stars, which we revisit here with the new high precision of the TESS data. Results. In addition to recovering the eight already known binaries in our sample, we find that 18 further central stars show clear signs of periodic variability in the TESS data, probably resulting from different physical effects compatible with the binary scenario. We propose them as new candidate binary central stars. We also discuss the origin of the detected variability in each particular case by using the TESS_localize algorithm. Finally, 12 targets show no or only weak evidence of variability at the sensitivity of TESS. Conclusions. Our study demonstrates the power of space-based photometric surveys in searching for close binary companions of central stars of PNe. Although our detections can only be catalogued as candidate binaries, we find a large percentage of possible stellar pairs associated with PNe, supporting the hypothesis that binarity plays a key role in shaping these celestial structures. [ABSTRACT FROM AUTHOR]

Context. Using data from eROSITA (extended Roentgen Survey with an Imaging Telescope Array) on board Spektrum-Roentgen- Gamma (Spektr-RG, SRG) taken during the first eROSITAall-sky survey (eRASS1), we performed the first X-ray classification and population study in the field of the Canis Major overdensity (CMa OD), which is an elliptical-shaped stellar overdensity located at l = -240°, b = −80°. Aims. This study aims to identify the X-ray sources in CMa OD. We developed a classification algorithm using multi-wavelength criteria as a preliminary method for the classification of faint X-ray sources, specifically in regions with a high source number density. Methods. We used the brightness of the multi-wavelength counterparts (mainly from infrared and optical catalogues), along with the X-ray flux and X-ray hardness ratios (HRs) to classify the sources. Results. Out of a total number of 8311 X-ray sources, we classified 1029 sources as Galactic stars and binaries in the foreground, 946 sources as active galactic nuclei (AGNs) and galaxies in the background, and 435 sources with stellar counterparts that may belong to either the MW or CMa OD. Among the sources with a stellar counterpart, we identified 34 symbiotic star candidates, plus 335 sources, of which the infrared (IR) counterparts have properties of M-giants in CMa OD. Moreover, there is a known high-mass X-ray binary (HMXB, 4U 0728-25) in the field of our study; according to the Gaia parallax of its companion, it appears to be a member of CMa OD. There is also a recently detected transient low-mass X-ray binary (LMXB, SRGt J071522.1-191609) is also present; it may be a member of CMa OD based on its companion, which is most likely highly absorbed and is thus located behind the Galactic disk. In addition, we present the X-ray luminosity function (XLF) of members and candidate members of CMa OD. It is dominated by sources with luminosities of <2 × 1032–1033 erg s−1 in the energy range of 0.2–2.3 keV. These sources are expected to be either accreting white dwarfs or quiescent LMXBs. [ABSTRACT FROM AUTHOR]

Context. Many fast-rotating stars (rotation periods of < 2 days) are found to be unresolved binaries with separations of tens of AU. This correlation between fast rotators and binarity leads to the question of whether the formation of binary stars inherently produces fast rotators. Aims. Our goal is to understand the spin evolution of protostars and whether the formation of companions plays a role in spinning up stars. Methods. We used magneto-hydrodynamic simulations to study the formation of multiple star systems from turbulent and non-turbulent protostellar cores. We tracked the angular momentum accreted by individual star and inner disc systems by using a sink (star) particle technique. We ran a resolution study to extrapolate protostellar properties. Results. We find in all simulations that the primary star can experience a spin-up event correlated with the formation of companions, namely fragmentation into binaries or higher-order systems. The primary star can spin up by up to 84% of its pre-fragmentation angular momentum and by up to 18% of its pre-fragmentation mass-specific angular momentum. The mechanism for the spin-up is gravitational disc instabilities in the circumstellar disc around the primary star, which leads to the accretion of material with high specific angular momentum. The simulations that experience the strongest disc instabilities fragment to form companions. Simulations with weaker spin-up events experience disc instabilities triggered by a companion flyby, and the disc instability in these cases typically does not produce further fragments (i.e. they remain binary systems). Conclusions. The primary star in multiple star systems can end up with a higher spin than single stars. This is because gravitational instabilities in the circumstellar disc around the primary star can trigger a spin-up event. In the strongest spin-up events, the instability is likely to cause disc fragmentation and the formation of companions. This spin-up mechanism, coupled with shorter disc lifetimes due to truncated circumstellar discs (and thus short spin-down times), may help produce fast rotators. [ABSTRACT FROM AUTHOR]

Context. The coincident detection of GW170817 and gamma-ray burst GRB170817A marked a milestone for the connection between binary neutron star (BNS) mergers and short gamma-ray bursts (sGRBs). These mergers can lead to the formation of a black hole that is surrounded by a disk and to the generation of a powerful jet. It spends energy to break free from the merger ejecta, and then a portion of it is dissipated to produce observable emissions. Aims. Our primary goal is to enhance our comprehension of BNS mergers by constraining the disk mass for a selection of sGRBs. To do this, we used the isotropic gamma-ray luminosity and corresponding emission times as key indicators. Methods. We leveraged data from GW170817 to estimate the disk mass surrounding the BNS merger remnant, and we subsequently inferred the efficiency of the accretion onto the jet. We then statistically examined other sGRB observations to estimate whether they might have been induced by BNS mergers Results. Our findings suggest that when similar physical parameters are employed as in the only observed BNS-powered GRB event, GRB170817A, a substantial fraction of sGRBs would need an unrealistically massive disk remnant. Conclusions. This observation raises the possibility that either a different mechanism powered those events or that the post-collapse disk efficiency varies significantly in different BNS merger scenarios. [ABSTRACT FROM AUTHOR]

Context. Extragalactic fast X-ray transients (FXTs) are short-duration (∼ks) X-ray flashes of unknown origin, potentially arising from binary neutron star (BNS) mergers, tidal disruption events, or supernova shock breakouts. Aims. In the context of the BNS scenario, we investigate the possible link between FXTs and the afterglows of off-axis merger-induced gamma-ray bursts (GRBs). Methods. By modelling well-sampled broadband afterglows of 13 merger-induced GRBs, we make predictions for their X-ray light curve behaviour had they been observed off-axis, considering both a uniform jet with core angle θC and a Gaussian-structured jet whose edge lies at an angle θW = 2θC. We compare their peak X-ray luminosity, duration, and temporal indices α (where F ∝ tα) with those of the currently known extragalactic FXTs. Results. Our analysis reveals that a slightly off-axis observing angle of θobs ≈ (2.2 − 3)θC and a structured jet are required to explain the shallow (|α|≲0.3) temporal indices of the FXT light curves, which cannot be reproduced in the uniform-jet case at any viewing angle. In the case of a structured jet with truncation angle θW = 2θC, the distributions of the duration of the FXTs are consistent with those of the off-axis afterglows for the same range of observing angles, θobs ≈ (2.2 − 3)θC. While the distributions of the off-axis peak X-ray luminosity are consistent only for θobs = 2.2θC, focussing on individual events with different intrinsic luminosities reveals that the match of all three properties (peak X-ray luminosity, duration and temporal indices) of the FXTs at the same viewing angle is possible in the range θobs ∼ (2.2 − 2.6)θC. Despite the small sample of GRBs analysed, these results show that there is a region of the parameter space – although quite limited – where the observational properties of off-axis GRB afterglow can be consistent with those of the newly discovered FXTs. Future observations of FXTs discovered by the recently launched Einstein Probe mission and GRB population studies combined with more complex afterglow models will shed light on this possible GRB-FXT connection, and eventually unveil the progenitors of some FXTs. [ABSTRACT FROM AUTHOR]

In this work we analyzed the long-term X-ray variation of Cir X-1 and its NICER spectra. The dip width and the peak flux after periastron are obtained. Our findings show a negative correlation between the dip width and the peak flux. A new scenario is introduced to explain the correlation. The disk height is higher at a larger radius in the standard model. When the neutron star (NS) moves away from periastron, the contraction of the equipotential surface causes the height of the outer disk to increase significantly. It blocks the X-ray emission near the NS. Subsequently, the height of the outer disk gradually decreases due to the viscosity. The viscous timescale is inversely proportional to the height of the disk, and the height of the outer disk is proportional to the mass transferred from the companion near periastron, thus the peak flux. Consequently, the duration of the obscuring, corresponding to the dip width, is inversely proportional to the peak flux. Moreover, we introduce a new ephemeris MJD(N) = 43075.0 + 16.5843N − 4.778 × 10−5N2 based on the dip-in phases (ingress phase of the dip). [ABSTRACT FROM AUTHOR]

Context. Constraining the coplanarity status of very low mass (VLM) tight binary systems provides valuable information towards understanding the dominant mechanisms in star and planetary formation at the lower end of the initial mass function. Aims. We sought to constrain the v sin i degeneracies of two nearby tight VLM binary systems, 2MASS J0746+20AB and 2MASS J1314+13AB, by independently determining each companion's rotational period and so characterize each system's spin-orbit alignment. Methods. Long observational baseline high cadence I band photometry data were obtained for both systems using the Galway Ultra Fast Imager (GUFI) on the Mount Graham International Observatory's Vatican Advanced Technology Telescope. Previously known rotational periods determined in other passbands were used as a basis for recovering additional periodic modulations in the time-series data. Results. Using the known rotational period of 3.32 hours for 2MASS J0746425+200032A, we recovered an underlying periodic modulation of 2.14 ± 0.11 hours, which we associate with 2MASS J0746425+200032B. Breaking each components' v sin i corresponds to equatorial inclination angles of 32 ± 4 degrees and 37 ± 4 degrees for components A & B respectively. We recover a weaker 2.06 ± 0.05 hours modulation separate from the known 3.79 hour signature for J1314203+132001B, which we associate with J1314203+132001A. We place a lower limit on J1314203+132001A's equatorial inclination angle to be in the range of 24.5−3+3.5 degrees, which deviates from the system's orbital plane previously determined to be 49.34−0.23+0.28 degrees. Conclusions. We confirm long term, consistent periodic modulations from both binary systems and report the first definitive rotational period for J1314203+132001A of 2.06 ± 0.05 hours, in addition to coplanarity to within 10 degrees in the spin-orbit alignment of the 2MASS J0746425+200032AB system. The lack of separate v sin i values for the 2MASS J1314203+132001AB system limits a definitive assessment but best estimates suggest coplanarity to be unlikely. [ABSTRACT FROM AUTHOR]

Context. Tidal deformation breaks the axisymmetric structure of stars, and this may affect stellar activity. This effect has been demonstrated in theoretical analyses and simulations, but it lacks observational support. In this paper, we use spot-modulated detached binaries to study the effect of tides on stellar activity. We show this effect by analyzing the properties of the spot lifetime, the harmonic decay timescale, and the orbital parameters. Aims. We aim to explore the differences in spot lifetimes between binaries and single stars, the main mechanisms of spot decay in binaries, and the correlation between orbital parameters and spot lifetimes. These differences will provide clues to the effect of tides on stellar activity. Methods. We collected data of 311 spot-modulated detached binaries and 3272 single stars. The relative orbital parameters of the binaries were derived by combining Kepler photometry, stellar atmospheric parameters from LAMOST DR9 and Gaia DR3, and 2MASS photometry. We then used the ACF method to obtain the rotational periods, lifetimes, and harmonic decay timescales. Finally, we analyzed the correlation between the lifetime of spots and orbital parameters, explored the dominant decay mechanism of spots, and examined the differences in spots for binaries and single stars. Results. The relative lifetime of a starspot is correlated with the sum of the fractional radii, the orbital eccentricity, and the synchronization ratio. Longer lifetimes are observed in close, circular, and synchronous binaries than in the other binaries. The main mechanism for the decay of star spots in binaries is large-scale convective motion. However, on close, cool, and fast-rotating binaries, horizontal diffusion or subphotospheric diffusion are dominant. Compared to single stars, the median lifetime of a starspot on binaries was found to be longer. Moreover, this difference decreases with rotation period. Additionally, it should be noted that spots on binaries experience increased horizontal or subphotospheric diffusion at the same rotation period and effective temperature. Conclusions. According to the observation results, we conclude that the lifetime of starspots on detached close binaries is affected by tidal interactions. [ABSTRACT FROM AUTHOR]

Context. With the advent of large spectroscopic surveys, automated stellar parameter determination has become commonplace. Nevertheless, spectral classification still offers a quick and useful alternative for obtaining parameter estimates for large samples of spectra of varying quality. Aims. We present a new atlas of stellar spectra covering the B-type range, with the intention of providing detailed classification criteria valid for modern spectra and improving the grid of reliable standards. This new grid will be used in future works to provide classification criteria beyond the classical classification range and addressing, in particular, the use of Gaia/RVS spectra. Methods. We analysed historical standards by means of multiple high-resolution spectra, marking out problematic cases and complementing the grid with a new set of reliable comparators. We then elaborated on a new set of classification criteria based on high-quality R = 4000 spectra. Results. Our new classification grid is much thicker than any previous set of standards, presenting a high degree of self-consistency. Although it is based entirely on morphological criteria, the grid demonstrates a much better correlation with different physical parameters. Conclusions. The new grid can be used to study classification criteria in other spectral ranges, providing a valuable tool for the study of B-type stars that covers a very wide range of temperatures, luminosities, and stellar masses. The very process of classification also offers valuable insights into stellar evolution. [ABSTRACT FROM AUTHOR]

Context. The existence of low-mass giants with large amounts of lithium (Li) in their surfaces has challenged stellar evolution for decades. One of the possibilities usually discussed in the literature to explain these Li-rich giants involves the interaction with a close binary companion, a scenario that predicts that, when compared against their non-enriched counterparts, Li-rich giants should preferentially be found as part of binary systems. Aims. We aim to assemble the largest possible sample of low-mass giants with well-measured Li abundances, to determine with high statistical significance the close binary fractions of Li-rich and Li-normal giants, and thus test the binary interaction scenario for the emergence of Li-rich giants. Methods. We developed a method that uses radial velocities (RVs) at three different epochs to quantify the degree of RV variability, which we used as a proxy for the presence of a close binary companion. The method was tested and calibrated against samples of known RV standard stars and known spectroscopic binaries. We then assembled a sample of 1418 giants with available RVs from RAVE, GALAH, and Gaia, as well as stellar parameters and Li abundances from GALAH, to which we applied our variability classification. We could determine an evolutionary state for 1030 of these giants. We also compared the results of our RV variability analysis with binarity indicators from the Gaia mission. Results. When applying our methodology to the control samples, we found that the accuracy of the classification is controlled by the precision of the RVs used in the analysis. For the set of RVs available for the giants, this accuracy is 80–85%. Consistent with seismic studies, the resulting sample of giants contains a fraction of Li-rich objects in the red clump (RC) that is twice as large as that in the first ascent red giant branch (RGB). Among RC giants, the fractions of Li-rich objects with a high RV variability and with no RV variability are the same as those for Li-normal objects, but we find some evidence that these fractions may be different for giants in the first-ascent RGB. Analysis of binary indicators in Gaia DR3 shows a smaller fraction of binary giants than our criteria, but no relation can be seen between Li enrichment and binarity either. Conclusions. Our RV variability analysis indicates that there is no preference for Li-rich giants in the RC to be part of binary systems, thus arguing against a binary interaction scenario for the genesis of the bulk of Li-rich giants at that evolutionary stage. On the other hand, Li-rich giants in the RGB appear to have a small but measurable preference for having close companions, something that deserves further scrutiny with more and better data. Additional measurements of the RVs of these giants at a higher RV precision would greatly help in confirming and more robustly quantifying these results. [ABSTRACT FROM AUTHOR]

We present a complete numerical model of the afterglow of a laterally structured relativistic ejecta from the radio to very high energies (VHE). This includes a self-consistent calculation of the synchrotron radiation, with its maximum frequency, and of synchrotron self-Compton (SSC) scattering that takes the Klein-Nishina regime into account. Attenuation due to pair production is also included. This model is computationally efficient and allows multi-wavelength data fitting. As a validation test, the radiative model was used to fit the broad-band spectrum of GRB 190114C at 90 s up to the TeV range. The full model was then used to fit the afterglow of GW 170817 and predict its VHE emission. We find that the SSC flux at the peak was much dimmer than the upper limit from H.E.S.S. observations. However, we show that either a smaller viewing angle or a higher external density would make similar off-axis events detectable in the future at VHE, even above 100 Mpc with the sensitivity of the Cherenkov telescope array. High external densities are expected in the case of fast mergers, but the existence of a formation channel for these binary neutron stars is still uncertain. We highlight that VHE afterglow detections would help to efficiently probe systems like this. [ABSTRACT FROM AUTHOR]

Core-collapse supernovae are explosions of massive stars at the end of their evolution. They are responsible for metal production and for halting star formation, having a significant impact on galaxy evolution. The details of these processes depend on the nature of supernova progenitors, but it is unclear if Type Ic supernovae (without hydrogen or helium lines in their spectra) originate from core-collapses of very massive stars (>30 M⊙) or from less massive stars in binary systems. Here we show that Type II (with hydrogen lines) and Ic supernovae are located in environments with similar molecular gas densities, therefore their progenitors have comparable lifetimes and initial masses. This supports a binary interaction for most Type Ic supernova progenitors, which explains the lack of hydrogen and helium lines. This finding can be implemented in sub-grid prescriptions in numerical cosmological simulations to improve the feedback and chemical mixing. Type Ic supernovae (SNe) originate either from the core collapse of very massive stars or from less massive stars in binary systems. Here, the authors show that progenitors of Type II and Ic SNe have comparable lifetimes and initial masses, which supports binary interaction for most Type Ic SNe progenitors. [ABSTRACT FROM AUTHOR]

This study presented the first light curve analysis of the OP Boo and V0511 Cam binary stars, which was conducted in the frame of the Binary Systems of South and North (BSN) Project. Photometric ground-based observations were conducted with standard filters at two observatories in the Czech Republic. We computed a new ephemeris for each of the systems using our extracted times of minima, TESS data, and additional literature. Linear fits for O-C diagrams of both systems were considered using the Markov Chain Monte Carlo (MCMC) method. The light curves were analyzed using the Wilson-Devinney (WD) binary code combined with the Monte Carlo (MC) simulation. The light curve solutions of both target systems required a cold starspot. The absolute parameters of the systems were calculated by using a P – M parameter relationship. The positions of the systems were also depicted on the Hertzsprung-Russell (HR), P - L, logMtot - logJ0, and T - M diagrams. The hotter component in both systems is determined to be a more massive star. Therefore, it can be concluded that both systems are W-type contact binary systems. [ABSTRACT FROM AUTHOR]

Reanalyzing contact binaries with space-based photometric data and investigating possible parameter changes can yield accurate samples for theoretical studies. We investigated light curve solutions and fundamental parameters for twenty contact binary systems. The most recent Transiting Exoplanet Survey Satellite (TESS) data is used to analyze. The target systems in the investigation have an orbital period of less than 0.58 days. Light curve solutions were performed using the PHysics Of Eclipsing BinariEs (PHOEBE) Python code version 2.4.9. The results show that systems had various mass ratios from q = 0.149 to q = 3.915, fillout factors (the degree of contact) from f = 0.072 to f = 0.566, and inclinations from i = 52°.8 to i = 87°.3. The effective temperature of the stars was less than 7016 K, which was expected given the features of most contact binary stars. Twelve of the target systems' light curves were asymmetrical in the maxima, showing the O'Connell effect, and a starspot was required for light curve solutions. The estimation of the absolute parameters of the binary systems was presented using the a - P empirical relationship and discussed. The orbital angular momentum J0 of the systems was calculated. The positions of the systems were also depicted on the M - L, M - R, q - Lratio, Mtot - J0, and T - M diagrams. [ABSTRACT FROM AUTHOR]

In 2011, Beeler and Hoilman generalized the game of peg solitaire to arbitrary connected graphs. Since then peg solitaire and related games have been considered on many graph classes. One of the main goals is the characterization of solvable graphs. To this end, different graph operations, such as joins and Cartesian products, have been considered in the past. In this article, we continue this venue of research by investigating line graphs. Instead of playing peg solitaire on the line graph L(G) of a graph G, we introduce a related game called stick solitaire and play it on G. This game is examined on several well-known graph classes, for example complete graphs and windmills. In particular, we prove that most of them are stick-solvable. We also present a family of graphs which contains unsolvable graphs in stick solitaire. Naturally, the fool's stick solitaire number is an object of interest, which we compute for the previously considered graph classes. [ABSTRACT FROM AUTHOR]

Binary star systems are expected to follow Newtonian dynamics similarly to planetary systems. However, reports have been made of wide binary systems with separations around 0.01 pc and larger, showing potential deviations from standard Newtonian motion. This phenomenon, suggestive of the flattening of galactic rotation curves, calls for closer inspection. This study presents an analysis of wide binary stars using data from Gaia Data Release 3 (DR3), a space-based astrometry mission funded by the European Space Agency. The study compares different choices of selection criteria to examine the nature of these apparent anomalous kinematics within the solar neighbourhood. The Gaia data set furnishes detailed parameters, including radial velocity, mass, age, and binary probability in addition to standard parameters. A custom Python tool named bynary facilitated both data processing and analysis. This report reveals that the signs of any anomalous signals systematically diminish as the initial selection criteria are relaxed for degrouping while subsequent filtering remains stringent, leading to the complete elimination of any apparent non-Newtonian motion for binary separations within 0.5 pc. The study shows that any observed anomalous behaviour in solar neighbourhood wide binaries within 130 pc must be produced either by faint companion stars orbiting primary or secondary stars, or by flyby stars. The findings emphasize the importance of the choice of selection criteria in disentangling genuine binary dynamics from external influences. The conclusions align with the predictions of Newtonian mechanics and general relativity, though they do not exclude other phenomena at larger scales. [ABSTRACT FROM AUTHOR]

The article discusses the integration of physics principles, engineering, and computer programming in pre-college classrooms. It highlights the importance of implementing integrated activities that incorporate physics concepts, engineering, and computer science to broaden STEM opportunities and increase students' interest in these disciplines. The article presents a unit that allows students to explore the inverse-square law by designing and building an illuminance-distance sensor using Arduino microcontrollers. The unit follows a five-phase instructional model and includes engaging students in discussions, exploring the relationship between illuminance and distance, explaining the concepts through data analysis, and evaluating and presenting findings. The article emphasizes the benefits of this approach in teaching STEM skills and habits of mind. [Extracted from the article]

We present our results on two Z Cam stars: Z Cam and AT Cnc. We apply observational data for the periods that cover the states of outbursts and standstills, which are typical for this type of object. We report an appearance of periodic oscillations in brightness during the standstill in AT Cnc, with small-amplitude variations of 0.03–0.04 mag and periodicity of ≈20–30 min. Based on the estimated dereddened color index (B − V)0, we calculate the color temperature for both states of the two objects. During the transition from the outburst to the standstill state, Z Cam varies from bluer to redder, while AT Cnc stays redder in both states. We calculate some of the stars' parameters as the radii of the primary and secondary components and the orbital separation for both objects. We construct the profiles of the effective temperature in the discs of the two objects. Comparing the parameters of both systems, we see that Z Cam is definitely the hotter object and we conclude that it has a more active accretion disc. [ABSTRACT FROM AUTHOR]

The planar Turán number of a graph H , denoted by e x P (n , H) , is the maximum number of edges in an n -vertex H -free planar graph. Recently, D. Ghosh, et al. initiated the topic of double stars and prove that e x P (n , S 2 , 5) ≤ 20 7 n. In this paper, we continue to study this and give a better upper bound e x P (n , S 2 , 5) ≤ 19 7 n − 18 7 for all n ≥ 1 , with equality when n = 12. This improves Ghosh's result. [ABSTRACT FROM AUTHOR]

Given a properly edge-colored graph F , we call it rainbow if all of its edges receive different colors. The maximum number of edges, denoted by ex ∗ (n , F) , in a properly edge-colored graph on n vertices which contains no rainbow F is called the rainbow Turán number of F. When the host graph is planar, we denote it as ex P ∗ (n , F). A graph obtained by taking an edge with s vertices joining one of its end vertices and k vertices joining the other end vertex is called an (s , k) -double star, dented by S s , k. In this paper, we study ex P ∗ (n , S 1 , k) for all k except k = 5 and ex P ∗ (n , S 2 , 2). [ABSTRACT FROM AUTHOR]

This article is an investigation of our mentoring relationship in the context of philosophically and theoretically informed qualitative research over the past several years. Specifically, we focus on our work as qualitative researchers from a variety of theoretical and philosophical standpoints. In this article, we think with two theoretical concepts: micro-ethical events and care as a world-making practice along with data from our years-long mentoring relationship. As a result, we describe how we discovered that it is the moments which initially seemed mundane which were most significant in mentoring. We name this contribution as mundane significance, describing three insights for the field of cultural studies: care-full reading practices, making the invisible, visible, and challenging mentor and mentee binaries. [ABSTRACT FROM AUTHOR]

We present our results on two Z Cam stars: Z Cam and AT Cnc. We apply observational data for the periods that cover the states of outbursts and standstills, which are typical for this type of object. We report an appearance of periodic oscillations in brightness during the standstill in AT Cnc, with small-amplitude variations of 0.03–0.04 mag and periodicity of ≈20–30 min. Based on the estimated dereddened color index (B − V)0, we calculate the color temperature for both states of the two objects. During the transition from the outburst to the standstill state, Z Cam varies from bluer to redder, while AT Cnc stays redder in both states. We calculate some of the stars’ parameters as the radii of the primary and secondary components and the orbital separation for both objects. We construct the profiles of the effective temperature in the discs of the two objects. Comparing the parameters of both systems, we see that Z Cam is definitely the hotter object and we conclude that it has a more active accretion disc.

How massive stars end their lives depends on the core mass, core angular momentum, and hydrogen envelopes at death. However, these key physical facets of stellar evolution can be severely affected by binary interactions. In turn, the effectiveness of binary interactions itself varies greatly depending on the initial conditions of the binaries, making the situation much more complex. We investigate systematically how binary interactions influence core–collapse progenitors and their fates. Binary evolution simulations are performed to survey the parameter space of supernova progenitors in solar metallicity binary systems and to delineate major evolutionary paths. We first study fixed binary mass ratios (⁠|$q=M_2/M_1$| = 0.5, 0.7, and 0.9) to elucidate the impacts of initial mass and initial separation on the outcomes, treating separately Type Ibc supernova, Type II supernova, accretion-induced collapse (AIC), rapidly rotating supernova (Ibc-R), black hole formation, and long gamma ray burst (long GRB). We then conduct 12 binary population synthesis model calculations, varying the initial condition distributions and binary evolution parameters, to estimate various supernova fractions. We obtain a Milky Way supernova rate |$R_{\rm SN} = (1.78$| – |$2.47) \times 10^{-2} \, {\rm yr}^{-1}$| which is consistent with observations. We find the rates of AIC, Ibc-R, and long GRB to be |$\sim 1/100$| the rate of regular supernovae. Our estimated long GRB rates are higher than the observed long GRB rate and close to the low luminosity GRB rate, although care must be taken considering our models are computed with solar metallicity. Furthering binary modelling and improving the inputs one by one will enable more detailed studies of these and other transients associated with massive stars. [ABSTRACT FROM AUTHOR]

Many of the most intriguing features, including spirals and cavities, in the current disc observations are found in binary systems like GG Tau, HD 142527, or HD 100453. Such features are evidence of the dynamic interactions between binary stars and the viscous disc. Understanding these dynamic interactions and how they result in the structure and growth of asymmetric circumbinary discs is a difficult problem, for which there is no complete analytical solution, that predicts the shape of the observed disc accurately. We use numerical simulations to evolve circumbinary discs with varying disc viscosities and investigate the size and shape of the inner cavities in such protoplanetary discs. We have simulated over 140 locally isothermal 2D grid-based disc models for |$\ge$| 3 × 104 binary orbits each and mapped out the parameter space relevant for protoplanetary discs. With this, it becomes possible to create parametrized profiles for individual discs to compare to observations and find limits to their binary eccentricity or internal viscosity from the simulation data. In the long-term simulations, larger cavity sizes than previously considered are possible within the parameter space (⁠|$\le$| 6 binary separations). As an example, we find that the eccentricity of the disc around HD 142527 suggests the impact of the binary dynamics on the disc. However, even considering the larger cavity sizes, the large size of the cavity in HD 142527 remains unexplained by the simulations considering the most recent orbital constraints. [ABSTRACT FROM AUTHOR]

Gaia wide stellar binaries (separations |$\sim 10^3{\!-\!}10^{4.5}$| au) are observed to have a superthermal eccentricity distribution function (DF), well-fit by |$P(e) \propto e^\alpha$| with |$\alpha \sim 1.2$|⁠. In a previous paper, we proved that this DF cannot have been produced by Galactic tidal torques starting from any realistic DF that was not already superthermal. Here, we consider the other major dynamical effect on wide binaries: encounters with passing stars. We derive and solve the Fokker–Planck equation governing the evolution of binaries in semimajor axis and eccentricity under many weak, impulsive, penetrative stellar encounters. We show analytically that these encounters drive the eccentricity DF towards thermal on the same time-scale as they drive the semimajor axes a towards disruption, |$t_\mathrm{dis}\sim 4\, \mathrm{Gyr}\, (a/10^4\, \mathrm{AU})^{-1}$|⁠. We conclude that the observed superthermal DF must derive from an even more superthermal (i.e. higher |$\alpha$|⁠) birth distribution. This requirement places strong constraints on the dominant binary formation channels. A testable prediction of our theory is that |$\alpha$| should be a monotonically decreasing function of binary age. [ABSTRACT FROM AUTHOR]

We present the first discoveries of the double-lined double white dwarf (DBL) survey that targets overluminous sources with respect to the canonical white dwarf cooling sequence according to a set of well-defined criteria. The primary goal of the DBL survey is to identify compact double white dwarf binary star systems from a unique spectral detection of both stars, which then enables a precise quantification of the atmospheric parameters and radial velocity variability of a system. Our search of 117 candidates that were randomly selected from a magnitude-limited sample of 399 yielded a 29 per cent detection efficiency with 34 systems exhibiting a double-lined signature. A further 38 systems show strong evidence of being single-lined or potentially DBL binaries and seven single-lined sources from the full observed sample are radial velocity variable. The 45 remaining candidates appear as a single WD with no companion or a non-DA white dwarf, bringing the efficiency of detecting binaries to 62 per cent. Atmospheric fitting of all double-lined systems reveals a large fraction that have two similar mass components that combine to a total mass of 1.0–1.3  |$\mathrm{M}_\odot$| – a class of double white dwarf binaries that may undergo a sub-Chandrasekhar mass type Ia detonation or merge to form a massive O/Ne WD, although orbital periods are required to infer on which time-scales. One double-lined system located 49 pc away, WDJ181058.67+311940.94, is super-Chandrasekhar mass, making it the second such double white dwarf binary to be discovered. [ABSTRACT FROM AUTHOR]

In 1905, a National Observatory for Canada was constructed to house a 15-inch equatorial telescope and other instruments in its complex. A Warner & Swasey telescope with a John A. Brashear lens was purchased and used for the study of the Moon, spectroscopic binary stars, and other pursuits. Curiously, the Brashear objective was unceremoniously replaced in 1958 with the world's largest apochromat. But there was no announcement in the Journals or even mention in the Observatory Annual Reports. Why replace the Brashear? And why no announcement? Was the Brashear defective? Was it assembled backwards? Was there something to hide? The personal papers and daily journals of the principal actors are examined to uncover the truth. [ABSTRACT FROM AUTHOR]

Progress in locating the X‐line on the magnetopause beyond the atypical due south interplanetary magnetic field (IMF) condition is hampered by the fact that the global plasma and field spatial distributions constraining where reconnection could develop on the magnetopause are poorly known. This work presents global maps of the magnetic shear, current density and reconnection rate, on the global dayside magnetopause, reconstructed from two decades of measurements from Cluster, Double Star, THEMIS and MMS missions. These maps, generated for various IMF and dipole tilt angles, offer a unique comparison point for models and observations. The magnetic shear obtained from vacuum magnetostatic draping is shown to be inconsistent with observed shear maps for IMF cone angles in 12.5° ± 2.5° ≤ |θco| ≤ 45° ± 5°. Modeled maximum magnetic shear lines fail to incline toward the equator as the IMF clock angle increases, in contrast to those from observations and MHD models. Reconnection rate and current density maps are closer together than they are from the shear maps, but this similarity vanishes for increasingly radial IMF orientations. The X‐lines maximizing the magnetic shear are the only ones to sharply turns toward and follow the anti‐parallel ridge at high latitude. We show the behavior of X‐lines with varying IMF clock and dipole tilt angles to be different as the IMF cone angle varies. Finally, we discuss a fundamental disagreement between X‐lines maximizing a given quantity on the magnetopause and predictions of local X‐line orientations. Key Points: Global dayside reconstructions of the magnetic reconnection rate, magnetic shear and current density is proposed from in situ measurementsThe interplanetary magnetic field cone angle is a key parameter controlling these spatial distribution and their evolution with the IMF orientation and dipole tiltA parametric survey shows how to distinguish candidate X lines maximizing globally these distributions [ABSTRACT FROM AUTHOR]

The presence of extended Main-Sequence Turn-Off (eMSTO) in the open clusters has been attributed to various factors, such as spread in rotation rates, binary stars, and dust-like extinction from stellar excretion discs. We present a comprehensive analysis of the eMSTO in the open cluster NGC 2355. Using spectra from the Gaia –European Southern Observatory (ESO) archives, we find that the stars in the red part of the eMSTO have a higher mean v sin i value of 135.3 |$\pm$| 4.6 km s |$^{-1}$| compared to the stars in the blue part that have an average v sin i equal to 81.3 |$\pm$| 5.6 km s |$^{-1}$|⁠. This suggests that the eMSTO in NGC 2355 is possibly caused by the spread in rotation rates of stars. We do not find any substantial evidence of the dust-like extinction from the eMSTO stars using ultraviolet data from the Swift survey. The estimated synchronization time for low-mass ratio close binaries in the blue part of the eMSTO suggests that they would be mostly slow-rotating if present. However, the stars in the blue part of the eMSTO are preferentially located in the outer region of the cluster indicating that they may lack low-mass ratio close binaries. The spread in rotation rates of eMSTO stars in NGC 2355 is most likely caused by the star-disc interaction mechanism. The stars in the lower main sequence beyond the eMSTO region of NGC 2355 are slow rotating (mean v sin i = 26.5 |$\pm$| 1.3 km s |$^{-1}$|⁠) possibly due to the magnetic braking of their rotations. [ABSTRACT FROM AUTHOR]

Over a quarter of white dwarfs have photospheric metal pollution, which is evidence for recent accretion of exoplanetary material. While a wide range of mechanisms have been proposed to account for this pollution, there are currently few observational constraints to differentiate between them. To investigate the driving mechanism, we observe a sample of polluted and non-polluted white dwarfs in wide binary systems with main-sequence stars. Using the companion stars' metallicities as a proxy for the white dwarfs' primordial metallicities, we compare the metallicities of polluted and non-polluted systems. Because there is a well-known correlation between giant planet occurrence and higher metallicity (with a stronger correlation for close-in and eccentric planets), these metallicity distributions can be used to probe the role of gas giants in white dwarf accretion. We find that the metallicity distributions of polluted and non-polluted systems are consistent with the hypothesis that both samples have the same underlying metallicity distribution. However, we note that this result is likely biased by several selection effects. Additionally, we find no significant trend between white dwarf accretion rates and metallicity. These findings suggest that giant planets are not the dominant cause of white dwarf accretion events in binary systems. [ABSTRACT FROM AUTHOR]

The discovery of the first pulsar in a binary star system, the Hulse–Taylor pulsar, 50 years ago opened up an entirely new field of experimental gravity. For the first time it was possible to investigate strong-field and radiative aspects of the gravitational interaction. Continued observations of the Hulse–Taylor pulsar eventually led, among other confirmations of the predictions of general relativity (GR), to the first evidence for the reality of gravitational waves. In the meantime, many more radio pulsars have been discovered that are suitable for testing GR and its alternatives. One particularly remarkable binary system is the Double Pulsar, which has far surpassed the Hulse–Taylor pulsar in several respects. In addition, binary pulsar-white dwarf systems have been shown to be particularly suitable for testing alternative gravitational theories, as they often predict strong dipolar gravitational radiation for such asymmetric systems. A rather unique pulsar laboratory is the pulsar in a hierarchical stellar triple, that led to by far the most precise confirmation of the strong-field version of the universality of free fall. Using radio pulsars, it could be shown that additional aspects of the Strong Equivalence Principle apply to the dynamics of strongly self-gravitating bodies, like the local position and local Lorentz invariance of the gravitational interaction. So far, GR has passed all pulsar tests with flying colours, while at the same time many alternative gravity theories have either been strongly constrained or even falsified. New telescopes, instrumentation, timing and search algorithms promise a significant improvement of the existing tests and the discovery of (qualitatively) new, more relativistic binary systems. [ABSTRACT FROM AUTHOR]

Context. The Gaia Collaboration has recently reported the detection of a 33 M⊙ black hole in a wide binary system located in the solar neighbourhood. Aims. Here we explore the relationship between this black hole, known as Gaia BH3, and the nearby ED-2 halo stellar stream. Methods. We studied the orbital characteristics of the Gaia BH3 binary and present measurements of the chemical abundances of ED-2 member stars derived from high-resolution spectra obtained with the VLT. Results. We find that the Galactic orbit of the Gaia BH3 system and its metallicity are entirely consistent with being part of the ED-2 stream. The characteristics of the stream, particularly its negligible spread in metallicity and in other chemical elements, as well as its single stellar population, suggest that it originated from a disrupted star cluster of low mass. Its age is comparable to that of the globular cluster M92 that has been estimated to be as old as the Universe. Conclusions. This is the first black hole unambiguously associated with a disrupted star cluster. We infer the plausible mass range for the cluster to be relatively narrow, between 2 × 103 M⊙ and 5.2 × 104 M⊙. This implies that the black hole could have formed directly from the collapse of a massive very metal-poor star, but that the alternative scenario of binary interactions inside the cluster environment also deserves to be explored. [ABSTRACT FROM AUTHOR]

Aims. We aim to investigate the theoretical possibility of accurately determining the helium-to-metal enrichment ratio ΔY/ΔZ from precise observations of double-lined eclipsing binary systems. Methods. Using Monte Carlo simulations, we drew synthetic binary systems with masses between 0.85 and 1.00 M⊙ from a grid of stellar models. Both stars were sampled from a grid with ΔY/ΔZ = 2.0, with a primary star at 80% of its main-sequence evolution. Subsequently, a broader grid with ΔY/ΔZ from 1.0 to 3.0 was used in the fitting process. To account for observational uncertainties, two scenarios were explored: S1, with realistic uncertainties of 100 K in temperature and 0.1 dex in [Fe/H]; and S2, with halved uncertainties. We repeated the simulation at two baseline metallicities: [Fe/H] = 0.0 and −0.3. Results. The posterior distributions of ΔY/ΔZ revealed significant biases. The distributions were severely biased towards the edge of the allowable range in the S1 error scenario. The situation only marginally improved when considering the S2 scenario. The effect is due to the impact of changing ΔY/ΔZ in the stellar effective temperature and its interplay with [Fe/H] observational error, and it is therefore not restricted to the specific fitting method. Despite the presence of these systematic discrepancies, the age of the systems were recovered unbiased with 10% precision. Conclusions. Our findings indicate that the observational uncertainty in effective temperature and metallicity significantly hinders the accurate determination of the ΔY/ΔZ parameter from main-sequence binary systems. [ABSTRACT FROM AUTHOR]

The SRG/eROSITA All-Sky Survey (eRASS) allows for the creation of a complete sample of X-ray dim isolated neutron stars (XDINSs), which will significantly facilitate the study of their population properties, evolution, and connection to other families of isolated neutron stars (INSs). In this work, we conduct a systematic search for XDINSs on the eROSITA western Galactic hemisphere down to an X-ray flux limit of 10−13 erg s−1 cm−2 and discuss the resulting candidate sample. Consistently with the properties of the known XDINSs, we selected all eRASS sources possessing a soft X-ray spectral distribution and that are unlikely to be associated with optical or infrared sources. Our selection criteria allowed us to recover all known XDINSs and previously proposed candidates. In addition, we put forward 33 new candidate members for dedicated follow-up identification campaigns. We found the resulting candidate sample to be about 30–50% complete, mainly due to source confusion and the stringent cross-matching criteria adopted to select the most promising candidates for immediate follow-up investigation. The candidates of the sample presented here can be broadly divided into two groups: 13 rather soft and 20 hot and somewhat hard X-ray emitters. Interestingly, the remarkably thermal nature of the candidates in the first group as well as their spatial distribution, lack of known counterparts, and absence of significant flux variability agree well with the properties of other confirmed thermally emitting INSs. For the candidates in the second group, the current observational data do not allow one to discern between rotation-powered or recycled pulsars, cataclysmic variables, or quiescent neutron stars in binary systems or even to rule out an extragalactic nature. On the basis of population synthesis and the estimated source completeness of the search, we expect that between one and three new XDINSs are among the already singled-out list of XDINS candidates – a long-sought increase in the proposed number of members of this elusive class of X-ray emitters. [ABSTRACT FROM AUTHOR]