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WR21 and WR31 are two WR + O binaries with short periods, quite similar to the case of V444 Cyg. The XMM-Newton observatory has monitored these two objects and clearly revealed phase-locked variations as expected from colliding winds. The changes are maximum in the soft band (0.5–2.0 keV, variations by a factor 3–4) where they are intrinsically linked to absorption effects. The increase in absorption due to the dense WR wind is confirmed by the spectral analysis. The flux maximum is however not detected exactly at conjunction with the O star in front but slightly afterwards, suggesting Coriolis deflection of the collision zone as in V444 Cyg. In the hard band (2–10 keV), the variations (by a factor of 1.5–2.0) are much more limited. Because of the lower orbital inclinations, eclipses as observed for V444 Cyg are not detected in these systems. [ABSTRACT FROM AUTHOR]

Exploring the low-mass end of the companion mass function around massive stars is of crucial importance to constrain massive star formation theories. We present a high-contrast imaging study of 20 O- and early B-type stars in the Scorpius OB1 association. From the analysis of VLT/SPHERE data, we identify a total of 789 sources. The data probe the brown dwarf regime around massive stars, resulting in the discovery of large-separation multiple systems with mass-ratios as low as 0.001 (comparable to Jupiter-Sun mass-ratio). [ABSTRACT FROM AUTHOR]

Most massive stars (up to 100%) are thought to be in binary systems. The multiplicity of massive stars seems to be intrinsically linked to their formation and evolution, and so Massive Young Stellar Objects are key in observing this early stage of star formation. We have surveyed hundreds of MYSOs across the Galaxy from the RMS catalogue, using UKIDSS and VVV point source data. Preliminary results show binary fractions of 44±3% for the UKIDSS sample and 32±3% for the VVV sample. In addition we use the K-band magnitudes as a proxy for the companion mass, and find a significant fraction of the detected companions have estimated mass ratios greater than 0.5, which suggests a deviation from the capture formation scenario. [ABSTRACT FROM AUTHOR]

On 2019 April 25, the LIGO/Virgo Scientific Collaboration detected a compact binary coalescence, GW190425. Under the assumption of the binary neutron star (BNS), the total mass of |$3.4^{+0.3}_{-0.1}\, \mathrm{M}_\odot$| lies five standard deviations away from the known Galactic population mean. In the standard common envelope scenario, the immediate progenitor of GW190425 is a close binary system composed of an NS and a He-rich star. With the detailed binary evolutionary modelling, we find that in order to reproduce GW190425-like events, super-Eddington accretion (e.g. |$1,000\, \dot{M}_{\rm Edd}$|⁠) from a He-rich star onto the first-born NS with a typical mass of 1.33 M⊙ via stable Case BB mass transfer (MT) is necessarily required. Furthermore, the immediate progenitors should potentially have an initial mass of M ZamsHe in a range of 3.0–3.5 M⊙ and an initial orbital period of P init from 0.08 d to 0.12 d, respectively. The corresponding mass accreted onto NSs via stable Case BB MT phase varies from |$0.70\, \mathrm{M}_\odot$| to |$0.77\, \mathrm{M}_\odot$|⁠. After the formation of the second-born NS, the BNSs are expected to be merged due to gravitational wave emission from ∼11 Myr to ∼190 Myr. [ABSTRACT FROM AUTHOR]

We use the three-dimensional Monte Carlo radiative transfer code hdust to model Be stars where the disc is tilted from the equatorial plane of the star. We compute 128 models across four spectral types, B0, B2, B5, and B8, tilting the disc by 0, 10○, 20○, and 40○, respectively, while varying disc density according to spectral type. We also compute every model for an average and high stellar rotation rate. We first discuss non-tilted disc temperatures and show its nonlinear dependence on stellar and disc parameters. We find that tilting the disc minimally affects the density-weighted average disc temperature, but tilting does create a temperature asymmetry in disc cross-sections, which is more pronounced for a faster rotation rate. We also investigate the effect tilting has on V -band magnitude, polarization, and the H |$\rm \alpha$| line. Tilting the disc does affect these observables, but the changes are entirely dependent on the position of the observer relative to the direction of tilt. We find the observables that distinguish tilting from a change in density or geometry are the H |$\rm \alpha$| line shapes, where it can transition between single-peaked and double-peaked, and the polarization position angle, whose value is dependent on the projected major elongation axis of the disc on the sky. We also present one early- and one late-type model with warped discs. We find their temperature structure varies a small amount from the uniformly tilted models, and the different observables correspond to different tilt angles, consistent with their expected volume of origin within the disc. [ABSTRACT FROM AUTHOR]

Gaia BH1, the first quiescent black hole (BH) detected from Gaia data, poses a challenge to most binary evolution models: its current mass ratio is ≈0.1, and its orbital period seems to be too long for a post-common envelope system and too short for a non-interacting binary system. Here, we explore the hypothesis that Gaia BH1 formed through dynamical interactions in a young star cluster (YSC). We study the properties of BH-main sequence (MS) binaries formed in YSCs with initial mass 3 × 102–3 × 104 M⊙ at solar metallicity, by means of 3.5 × 104 direct N -body simulations coupled with binary population synthesis. For comparison, we also run a sample of isolated binary stars with the same binary population synthesis code and initial conditions used in the dynamical models. We find that BH-MS systems that form via dynamical exchanges populate the region corresponding to the main orbital properties of Gaia BH1 (period, eccentricity, and masses). In contrast, none of our isolated binary systems match the orbital period and MS mass of Gaia BH1. Our best-matching Gaia BH1-like system forms via repeated dynamical exchanges and collisions involving the BH progenitor star, before it undergoes core collapse. YSCs are at least two orders of magnitude more efficient in forming Gaia BH1-like systems than isolated binary evolution. [ABSTRACT FROM AUTHOR]

Baikal-GVD has recently published its first measurement of the diffuse astrophysical neutrino flux, performed using high-energy cascade-like events. We further explore the Baikal-GVD cascade data set collected in 2018–2022, with the aim to identify possible associations between the Baikal-GVD neutrinos and known astrophysical sources. We leverage the relatively high angular resolution of the Baikal-GVD neutrino telescope (2–3 deg.), made possible by the use of liquid water as the detection medium, enabling the study of astrophysical point sources even with cascade events. We estimate the telescope's sensitivity in the cascade channel for high-energy astrophysical sources and refine our analysis prescriptions using Monte-Carlo simulations. We primarily focus on cascades with energies exceeding 100 TeV, which we employ to search for correlation with radio-bright blazars. Although the currently limited neutrino sample size provides no statistically significant effects, our analysis suggests a number of possible associations with both extragalactic and Galactic sources. Specifically, we present an analysis of an observed triplet of neutrino candidate events in the Galactic plane, focusing on its potential connection with certain Galactic sources, and discuss the coincidence of cascades with several bright and flaring blazars. [ABSTRACT FROM AUTHOR]

Here, we present the results of our multiwavelength campaign aimed at classifying Swift J170800−402551.8 as part of the Swift Deep Galactic Plane Survey (DGPS). We utilized Target of Opportunity (ToO) observations with the Neil Gehrels Swift Observatory, Chandra X-ray Observatory , Neutron star Interior Composition Explorer (NICER), X-ray Multi-Mirror Mission (XMM–Newton), Nuclear Spectroscopic Telescope Array (NuSTAR), and the Southern African Large Telescope (SALT), as well as multiwavelength archival observations from Gaia , VST Photometric Hα Survey, and VISTA Variables in the Via Lactea. The source displays a periodicity of 784 s in our XMM–Newton observation. The X-ray spectrum (XMM–Newton and NuSTAR) can be described by thermal bremsstrahlung radiation with a temperature of kT ≈ 30 keV. The phase-folded X-ray light curve displays a double-peaked, energy-dependent pulse profile. We used Chandra to precisely localize the source, allowing us to identify and study the multiwavelength counterpart. Spectroscopy with SALT identified a Balmer H α line, and potential He  i lines, from the optical counterpart. The faintness of the counterpart (r ≈ 21 AB mag) favours a low-mass donor star. Based on these criteria, we classify Swift J170800−402551.8 as a candidate intermediate polar cataclysmic variable, where the spin period of the white dwarf is 784 s. [ABSTRACT FROM AUTHOR]

We investigate the orbital stability of a tilted circumbinary planetary system with three giant planets. The planets are spaced by a constant number (Δ) of mutual Hill radii in the range Δ = 3.4–12.0 such that the period ratio of the inner pair is the same as that of the outer pair. A tilted circumbinary planetary system can be unstable even if the same system around a coplanar binary is stable. For an equal-mass binary, we find that the stability of a three-planet system is qualitatively similar to that of a two-planet system, but the three-planet system is more unstable in mean motion resonance regions. For an unequal-mass binary, there is significantly more instability in the three-planet system as the inner planets can undergo von Zeipel–Kozai–Lidov oscillations. Generally in unstable systems, the inner planets are more likely to be ejected than the outer planets. The most likely unstable outcome for closely spaced systems, with Δ ≲ 8, is a single remaining stable planet. For more widely separated systems, Δ ≳ 8, the most likely unstable outcome is two stable planets, only one being ejected. An observed circumbinary planet with significant eccentricity may suggest that it was formed from an unstable system. Consequently, a binary can host three tilted giant planets if the binary stars are close to equal mass and provided that the planets are well spaced and not close to a mean motion resonance. [ABSTRACT FROM AUTHOR]

By comparing the physical properties of pulsars hosted by core-collapsed (CCed) and non-core-collapsed (non-CCed) globular clusters (GCs), we find that pulsars in CCed GCs rotate significantly slower than their counterparts in non-CCed GCs. Additionally, radio luminosities at 1.4 GHz in CCed GCs are higher. These findings are consistent with the scenario that dynamical interactions in GCs can interrupt angular momentum transfer processes and surface magnetic field decay during the recycling phase. Our results suggest that such effects in CCed GCs are stronger due to more frequent disruptions of compact binaries. This is further supported by the observation that both estimated disruption rates and the fraction of isolated pulsars are predominantly higher in CCed GCs. [ABSTRACT FROM AUTHOR]

Simulations of the effects of stellar fly-bys on planetary systems in star-forming regions show a strong dependence on subtle variations in the initial spatial and kinematic substructure of the regions. For similar stellar densities, the more substructured star-forming regions disrupt up to a factor of 2 more planetary systems. We extend this work to look at the effects of substructure on stellar binary populations. We present N -body simulations of substructured, and non-substructured (smooth) star-forming regions in which we place different populations of stellar binaries. We find that for binary populations that are dominated by close (<100 au) systems, a higher proportion are destroyed in substructured regions. However, for wider systems (>100 au), a higher proportion are destroyed in smooth regions. The difference is likely due to the hard–soft or fast–slow boundary for binary destruction. Hard (fast/close) binaries are more likely to be destroyed in environments with a small velocity dispersion (kinematically substructured regions), whereas soft (slow/wide) binaries are more likely to be destroyed in environments with higher velocity dispersions (non-kinematically substructured regions). Due to the vast range of stellar binary semimajor axes in star-forming regions (10−2 to 104 au), these differences are small and hence unlikely to be observable. However, planetary systems have a much smaller initial semimajor axis range (likely ∼1–100 au for gas giants) and here the difference in the fraction of companions due to substructure could be observed if the star-forming regions that disrupt planetary systems formed with similar stellar densities. [ABSTRACT FROM AUTHOR]

The dynamical stability of quadruple-star systems has traditionally been treated as a problem involving two 'nested' triples which constitute a quadruple. In this novel study, we employed a machine learning algorithm, the multilayer perceptron (MLP), to directly classify 2 + 2 and 3 + 1 quadruples based on their stability (or long-term boundedness). The training data sets for the classification, comprised of 5 × 105 quadruples each, were integrated using the highly accurate direct N -body code mstar. We also carried out a limited parameter space study of zero-inclination systems to directly compare quadruples to triples. We found that both our quadruple MLP models perform better than a 'nested' triple MLP approach, which is especially significant for 3 + 1 quadruples. The classification accuracies for the 2 + 2 MLP and 3 + 1 MLP models are 94 and 93 per cent, respectively, while the scores for the 'nested' triple approach are 88 and 66 per cent, respectively. This is a crucial implication for quadruple population synthesis studies. Our MLP models, which are very simple and almost instantaneous to implement, are available on Github, along with python3 scripts to access them. [ABSTRACT FROM AUTHOR]

LS I +61°303 is a rare representative of the gamma-ray binaries with a compact object known to be a pulsar. We report on the periodicity and spectral analysis of this source performed with more than 14 yr of Fermi/LAT data. The periodicity of LS I +61°303 is strongly energy dependent. Two periods P 1 = 26.932 ± 0.004(stat) ± 0.008(syst) and P 2 = 26.485 ± 0.004(stat) ± 0.007(syst) are detected only at E > 1 GeV and at E < 0.3 GeV correspondingly. Within 1σ (stat  +  syst) the periods are consistent with orbital (P 2) and beat orbital/superorbital (P 1) periods. We present the orbital light curves of the system in several energy bands and the results of the spectral analysis. We discuss the possible origin of the change in the variability pattern between 0.1 and 1 GeV energy. [ABSTRACT FROM AUTHOR]

The origin of rapid rotation in massive stars remains debated, although binary interactions are now often advocated as a cause. However, the broad and shallow lines in the spectra of fast rotators make direct detection of binarity difficult. In this paper, we report on the discovery and analysis of multiplicity for three fast-rotating massive stars: HD 25631 (B3V), HD 191495 (B0V), and HD 46485 (O7V). They display strikingly similar TESS light curves, with two narrow eclipses superimposed on a sinusoidal variation due to reflection effects. We complement these photometric data by spectroscopy from various instruments (X-Shooter, Espadons, FUSE...), to further constrain the nature of these systems. The detailed analyses of these data demonstrates that the companions of the massive OB stars have low masses (∼1 M⊙) with rather large radii (2–4 R⊙) and low temperatures (<15 kK). These companions display no UV signature, which would exclude a hot subdwarf nature, but disentangling of the large set of X-Shooter spectra of HD 25631 revealed the typical signature of chromospheric activity in the companion's spectrum. In addition, despite the short orbital periods (P  = 3−7 d), the fast-rotating OB-stars still display non-synchronized rotation and all systems appear young (<20 Myr). This suggests that, as in a few other cases, these massive stars are paired in those systems with non-degenerate, low-mass PMS companions, implying that fast rotation would not be a consequence of a past binary interactions in their case. [ABSTRACT FROM AUTHOR]

Blue metal-poor (BMP) stars are the main-sequence stars that appear bluer and more luminous than normal turn-off stars of metal-poor globular clusters. They are believed to be either field blue straggler stars (FBSS) formed via post-mass transfer mechanism or accreted from dwarf satellite galaxies of the Milky Way. A significant fraction of BMP stars are discovered to be potential binaries. We observed 27 BMP stars using UVIT / AstroSat in two FUV filters, F148W and F169M. We report the discovery of white dwarf (WD) companions of 12 BMP stars for the first time. The WD companions have estimated temperatures Teff ∼10 500–18 250 K, and masses 0.17–0.8 M⊙. Based on [Fe/H] and space velocity, we group the 12 BMP/FBSS stars as the thick disc (5) and halo (5), whereas two stars appear to be in-between. All the 5 thick disc BMP/FBSS have extremely low-mass (M < 0.2 M⊙) WDs as companions, whereas the 5 halo BMP/FBSS have low (0.2 M⊙ < M < 0.4 M⊙), normal (0.4 M⊙ < M < 0.6 M⊙), and high mass (M > 0.6 M⊙) WD companions. Our analysis suggests that at least ∼44 |${{\ \rm per\ cent}}$| of BMP stars are FBSS, and these stars hold the key to understand the details of mass transfer, binary properties, and chemical enrichment among the FBSS. [ABSTRACT FROM AUTHOR]

Massive stars are the progenitors of black holes and neutron stars, the mergers of which can be detected with gravitational waves (GW). The expansion of massive stars is one of the key factors affecting their evolution in close binary systems, but it remains subject to large uncertainties in stellar astrophysics. For population studies and predictions of GW sources, the stellar expansion is often simulated with the analytic formulae from Hurley et al. (2000). These formulae need to be extrapolated and are often considered outdated. In this work, we present five different prescriptions developed from 1D stellar models to constrain the maximum expansion of massive stars. We adopt these prescriptions to investigate how stellar expansion affects mass transfer interactions and in turn the formation of GW sources. We show that limiting radial expansion with updated 1D stellar models, when compared to the use of Hurley et al. (2000) radial expansion formulae, does not significantly affect GW source properties (rates and masses). This is because most mass transfer events leading to GW sources are initialized in our models before the donor star reaches its maximum expansion. The only significant difference was found for the mass distribution of massive binary black hole mergers (M tot > 50 M⊙) formed from stars that may evolve beyond the Humphreys–Davidson limit, whose radial expansion is the most uncertain. We conclude that understanding the expansion of massive stars and the origin of the Humphrey–Davidson limit is a key factor for the study of GW sources. [ABSTRACT FROM AUTHOR]

In this population synthesis work, we study a variety of possible origin channels of supernovae type Ia (SNe Ia). Among them mergers of carbon–oxygen (CO) and oxygen–neon (ONe) white dwarfs (WDs) under the influence of gravitational waves are considered as the primary channel of SNe Ia formation. We estimated frequencies of mergers of WDs with different chemical compositions and distributions of masses of merging WDs. We computed the dependence of the ratio of merger frequencies of ONe and CO WDs as primaries in corresponding binaries on time. The scatter of masses of considered sources (up to the factor 1.5–2) of SNe Ia is important and should be carefully studied with other sophisticated methods from theoretical point of view. Our 'game of parameters' potentially explains the increased dimming of SNe Ia in the redshift range z ≈ 0.5–1 by the changes in the ratio of ONe and CO WDs, i.e. to describe the observed accelerated expansion of the Universe in terms of the evolution of properties of SNe Ia instead of cosmological explanations. This example shows the extreme importance of theoretical studies of problems concerning SNe Ia, because evolutionary scenario and parameter games in nature potentially lead to confusions in their empirical standardization and, therefore, they can influence on cosmological conclusions. [ABSTRACT FROM AUTHOR]

Massive binaries are vital sources of various transient processes, including gravitational-wave mergers. However, large uncertainties in the evolution of massive stars, both physical and numerical, present a major challenge to the understanding of their binary evolution. In this paper, we upgrade our interpolation-based stellar evolution code metisse to include the effects of mass changes, such as binary mass transfer or wind-driven mass loss, not already included within the input stellar tracks. metisse 's implementation of mass loss (applied to tracks without mass loss) shows excellent agreement with the sse fitting formulae and with detailed mesa tracks, except in cases where the mass transfer is too rapid for the star to maintain equilibrium. We use this updated version of metisse within the binary population synthesis code bse to demonstrate the impact of varying stellar evolution parameters, particularly core overshooting, on the evolution of a massive (25 and 15 M⊙) binary system with an orbital period of 1800 d. Depending on the input tracks, we find that the binary system can form a binary black hole or a black hole–neutron star system, with primary (secondary) remnant masses ranging between 4.47 (1.36) and 12.30 (10.89) M⊙, and orbital periods ranging from 6 d to the binary becoming unbound. Extending this analysis to a population of isolated binaries uniformly distributed in mass and orbital period, we show that the input stellar models play an important role in determining which regions of the binary parameter space can produce compact binary mergers, paving the way for predictions for current and future gravitational-wave observatories. [ABSTRACT FROM AUTHOR]

The Gaia eDR3 catalogue has recently been used to study statistically the internal kinematics of wide binary populations using relative velocities of the two component stars, Δ V , total binary masses, mB , and separations, s. For s ≳ 0.01 pc, these binaries probe the low-acceleration a ≲ 2 a 0 regime where gravitational anomalies usually attributed to dark matter are observed in the flat rotation curves of spiral galaxies, where a 0 ≈ 1.2 × 10−10 m s−2 is the acceleration scale of MOND. Such experiments test the degree of generality of these anomalies, by exploring the same acceleration regime using independent astronomical systems of vastly smaller mass and size. A signal above Newtonian expectations has been observed when a ≲ 2 a 0, alternatively interpreted as evidence of a modification of gravity, or as due to kinematic contaminants; undetected stellar components, unbound encounters, or spurious projection effects. Here I take advantage of the enhanced DR3 Gaia catalogue to perform a more rigorous study of the internal kinematics of wide binaries than what has previously been possible. Internally determined Gaia stellar masses and estimates of binary probabilities for each star using spectroscopic information, together with a larger sample of radial velocities, allow for a significant improvement in the analysis and careful exclusion of possible kinematic contaminants. Resulting Δ V scalings accurately tracing Newtonian expectations for the high acceleration regime, but markedly inconsistent with these expectations in the low acceleration one, are obtained. A non-Newtonian low acceleration phenomenology is thus confirmed. [ABSTRACT FROM AUTHOR]

The magnetic activity of low-mass stars changes as they age. The primary process decreasing the stellar activity level is the angular momentum loss via magnetized stellar wind. However, processes like tidal interactions between stars and their close companions may slow down the braking effect and the subsequent decrease of the activity level. Until now, the tidal impact of substellar objects like brown dwarfs on the evolution of their central stars has not been quantified. Here, we analyse the X-ray properties of NLTT 41135, an M dwarf tightly orbited by a brown dwarf, to determine the impact of tidal interactions between them. We find that NLTT 41135 is more than an order of magnitude brighter in the X-ray regime than its stellar companion, NLTT 41136, also an M dwarf star, with whom it forms a wide binary system. To characterize the typical intrinsic activity scatter between coeval M dwarf stars, we analyse a control sample of 25 M dwarf wide binary systems observed with the XMM–Newton and Chandra telescopes and the eROSITA instrument onboard the Spectrum Röntgen Gamma satellite. The activity difference in the NLTT 41135/41136 system is a 3.44σ outlier compared to the intrinsic activity scatter of the control systems. Therefore, the most convincing explanation for the observed activity discrepancy is tidal interactions between the M dwarf and its brown dwarf. This shows that tidal interactions between a star and a substellar companion can moderately alter the expected angular-momentum evolution of the star, making standard observational proxies for its age, such as X-ray emission, unreliable. [ABSTRACT FROM AUTHOR]

White dwarfs (WDs) in active galactic nucleus (AGN) discs might migrate to the inner radii of the discs and form restricted three-body systems with two WDs moving around the central supermassive black hole (SMBH) in close orbits. These systems could be dynamically unstable, which can lead to very close encounters or direct collisions. In this work, we use N -body simulations to study the evolution of such systems with different initial orbital separation p , relative orbital inclination Δ i , and SMBH mass M. It is found that close encounters of WDs occur mainly at |$1.1R_{\rm H} \lesssim p \lesssim 2\sqrt{3}R_{\rm H}$|⁠ , where R H is the mutual Hill radius. For p < 1.1 R H, the majority of WDs move in horseshoe or tadpole orbits, and only few of them with small initial orbital phase difference undergo close encounters. For p = 3.0 R H, WD–WD collisions occur in most of the samples within a time 105 P 1, and considerable collisions occur within a time t < 62 P 1 for small orbital radii, where P 1 is the orbital period. The peak of the closest separation distribution increases and the WD–WD collision fraction decreases with an increase in relative inclination. The closest separation distribution is similar in cases with different SMBH mass, but the WD–WD collision fraction decreases as the mass of SMBHs increases. According to our estimation, the event rate of cosmic WD–WD collisions in AGN discs is about 300 Gpc−3 yr−1, roughly 1 per cent of that of observed Type Ia supernovae. The corresponding electromagnetic emission signals can be observed through large surveys of AGNs. [ABSTRACT FROM AUTHOR]

The values of the bending delays in the signal of a radio pulsar in a binary with a stellar mass black hole as a companion have been calculated accurately within a full general relativistic framework considering the Schwarzchid spacetime near the companion. The results match with the pre-existing approximate analytical expressions unless both of the orbital inclination angle and the orbital phase are close to 90°. For such a case, the approximate analytical expressions underestimate the value of the bending delay. On the other hand, for systems like the double pulsar, those expressions are valid throughout the orbital phase, unless its inclination angle is very close to 90°. For a pulsar-black hole binary, the bending phenomenon also increases the strength of the pulse profile and sometimes can lead to a small low intensity tail. [ABSTRACT FROM AUTHOR]

The quest for quiet or dormant black holes has been ongoing since several decades. Ellipsoidal variables possibly indicate the existence of a very high-mass invisible companion and are thought to be one of the best ways to find such dormant black holes. This, however, is not a panacea as we show here with one example. We indeed report the discovery of a new semidetached interacting binary, V1315 Cas, discovered as an ellipsoidal variable. Using data from photometric surveys (ASAS-SN, TESS) and high-resolution spectroscopy, we derived a nearly circular orbit with an orbital period of P orb = 34.54 d. The binary system consists of an evolved F-type star primary that is likely still filling its Roche lobe and a B-type star secondary. Using phoebe 2, we derived the following masses and radii: for the primary, |$M_p =0.84 \pm 0.03 \, \rm {M}_{\odot}$| and |$R_p =18.51^{+0.12}_{-0.07} \, \rm {R}_{\odot}$|⁠ ; for the secondary, |$M_s =7.3 \pm 0.3 \, \rm {M}_{\odot}$|  and |$R_s =4.02^{+2.3}_{-2.0}\, \rm {R}_{\odot}$|⁠. Modelling the evolution of the system with mesa , we found an age of ∼7.7 × 107 yr. The system is at the end of a period of rapid non-conservative mass transfer that reversed its mass ratio, while significantly widening its orbit. The primary shows carbon depletion and nitrogen overabundance, indicative of CNO-processed material being exposed due to mass transfer. An infrared excess and stationary H α emission suggest the presence of a circumstellar or circumbinary disc. V1315 Cas will likely become a detached stripped star binary. [ABSTRACT FROM AUTHOR]

The high-precision astrometric mission GAIA recently reported the remarkable discovery of a Sun-like star closely orbiting a dark object with a semimajor axis and period of 1.4 au and 187.8 d, respectively. While the plausible expectation for the central dark object is a black hole, the evolutionary mechanism leading to the formation of such a two-body system is highly challenging. Here, we challenge the scenario of a central black hole and show that the observed orbital dynamics can be explained under fairly general assumptions if the central dark object is a stable clump of bosonic particles of spin-0 or spin-1, known as a boson star. Aside from possible formation mechanisms leading to a star orbiting a boson star, we show that the theory space of boson stars allows for a fairly natural mimicker of binary observations such as the recent one by GAIA. We further explain how future astrometric measurements of similar systems will provide an exciting opportunity to probe the fundamental nature of compact objects and test compact alternatives to black holes. [ABSTRACT FROM AUTHOR]

We present multi-epoch spectroscopic follow-up of a sample of ellipsoidal variables selected from Gaia Data Release 3 (DR3) as candidates for hosting quiescent black holes (BHs) and neutron stars (NSs). Our targets were identified as BH/NS candidates because their optical light curves – when interpreted with models that attribute variability to tidal distortion of a star by a companion that contributes negligible light – suggest that the companions are compact objects. From the likely BH/NS candidates identified in recent work accompanying Gaia DR3, we select 14 of the most promising targets for follow-up. We obtained spectra for each object at 2–10 epochs, strategically observing near conjunction to best constrain the radial velocity semi-amplitude. From the measured semi-amplitudes of the radial velocity curves, we derive minimum companion masses of |$M_{2,\, \rm min} \le 0.5 \, {\rm M}_{\odot }$| in all cases. Assuming random inclinations, the typical inferred companion mass is |$M_2 \sim 0.15\, {\rm M}_{\odot }$|⁠. This makes it unlikely that any of these systems contain a BH or NS, and we consider alternative explanations for the observed variability. We can best reproduce the observed light curves and radial velocities with models for unequal-mass contact binaries with star-spots. Some of the objects in our sample may also be detached main-sequence binaries, or even single stars with pulsations or star-spot variability masquerading as ellipsoidal variation. We provide recommendations for future spectroscopic efforts to further characterize this sample and more generally to search for compact object companions in close binaries. [ABSTRACT FROM AUTHOR]

We present the results of optical spectroscopy of stellar companions to three binary millisecond pulsars, PSRs J0621+2514, J2317+1439, and J2302+4442, obtained with the Gran Telescopio Canarias. The spectrum of the J0621+2514 companion shows a blue continuum and prominent Balmer absorption lines. The latter are also resolved in the spectrum of the J2317+1439 companion, showing that both are DA-type white dwarfs. No spectral features are detected for the J2302+4442 companion; however, its broad-band magnitudes and the spectral shape of the continuum emission imply that this is also a DA-type white dwarf. Based on the spectral analyses, we conclude that the companions of J0621+2514 and J2317+1439 are relatively hot, with effective temperatures T eff = 8600 ± 200 and 9600 ± 2000 K, respectively, while the J2302+4442 companion is significantly cooler, T eff<6000 K. We also estimated the distance to J0621+2514 of 1.1 ± 0.3 kpc and argue that its companion and the companion of J2317+1439 are He-core white dwarfs providing constraints on their cooling ages of |$\lesssim$| 2 Gyr. [ABSTRACT FROM AUTHOR]

A major puzzle concerning the wide stellar binaries (semimajor axes a ≳ 103 au) in the Solar neighbourhood is the origin of their observed superthermal eccentricity distribution function (DF), which is well approximated by P (e) ∝ e α with α ≈ 1.3. This DF evolves under the combined influence of (i) tidal torques from the Galactic disc and (ii) scattering by passing stars, molecular clouds, and substructure. Recently, it was demonstrated that Galactic tides alone cannot produce a superthermal eccentricity DF from an initially isotropic, non-superthermal one, under the restrictive assumptions that the eccentricity DF was initially of power-law form and then was rapidly phase-mixed toward a steady state by the tidal perturbation. In this paper, we first prove analytically that this conclusion is valid at all times, regardless of these assumptions. We then adopt a thin Galactic disc model and numerically integrate the equations of motion for several ensembles of tidally perturbed wide binaries to study the time evolution in detail. We find that even non-power-law DFs can be described by an effective power-law index α eff which accurately characterizes both their initial and final states, and that a DF with initial (effective or exact) power-law index α i is transformed by Galactic tides into another power law with index α f ≈ (1 + α i)/2 on a time-scale |$\sim 4\, \mathrm{Gyr}\, (a/10^4\mathrm{AU})^{-3/2}$|⁠. In a companion paper, we investigate separately the effect of stellar scattering. As the GAIA data continues to improve, these results will place strong constraints on wide binary formation channels. [ABSTRACT FROM AUTHOR]

Dark matter in the form of compact objects with mass M co ≳ 10 M⊙ can be constrained by its dynamical effects on wide binary stars. Motivated by the recent interest in primordial black hole dark matter, we revisit the theoretical modelling involved in these constraints. We improve on previous studies in several ways. Specifically, we (i) implement a physically motivated model for the initial wide-binary semimajor axis distribution, (ii) include unbound binaries, and (iii) take into account the uncertainty in the relationship between semimajor axis and observed angular separation. These effects all tend to increase the predicted number of wide binaries (for a given compact object population). Therefore, the constraints on the halo fraction in compact objects, f co, are significantly weakened. For the wide binary sample used in the most recent calculation of the constraints, we find the fraction of halo dark matter in compact objects is f co < 1 for |$M_{\rm co} \approx 300 \, \mathrm{ M}_{\odot }$|⁠ , tightening with increasing M co to f co < 0.26 for |$M_{\rm co} \gtrsim 1000 \, \mathrm{ M}_{\odot }$|⁠. [ABSTRACT FROM AUTHOR]

We study the Laser Interferometer Space Antenna (LISA) sources that arise from isolated binary evolution, and how these depend on age and metallicity, using model stellar populations from bpass. We model these as single-aged populations which are analogous to star clusters. We calculate the combined gravitational wave (GW) spectrum of all the binaries within these model clusters, including all types of compact binaries as well as those with living stars. These results allow us to evaluate the detectability of star clusters with LISA. We find at late times the dominant sources are WD–WD binaries by factors of 50–200, but at times between 108 and 109 yr we find a significant population of NS–WD and BH–WD binaries (2–40 per 106 M⊙), which is related to the treatment of mass transfer and common-envelope events in bpass , wherein mass transfer is relatively likely to be stable. Metallicity also has an effect on the GW spectrum and on the relative dominance of different types of binaries. Using the information about known star clusters will aid the identification of sky locations where one could expect LISA to find GW sources. [ABSTRACT FROM AUTHOR]

Motivated by the increasing number of detections of merging black holes by LIGO-VIRGO-KAGRA, black hole (BH) binary mergers in the discs of active galactic nuclei (AGNs) is investigated as a possible merger channel. In this pathway, BH encounters in the gas disc form mutually bound BH binary systems through interaction with the gas in the disc and subsequently inspiral through gravitational torques induced by the local gas. To determine the feasibility of this merger pathway, we present the first three-dimensional global hydrodynamic simulations of the formation and evolution of a stellar-mass BH binaries AGN discs with three different AGN disc masses and five different initial radial separations. These 15 simulations show binary capture of prograde and retrograde binaries can be successful in a range of disc densities including cases well below that of a standard radiatively efficient alpha disc, identifying that the majority of these captured binaries are then subsequently hardened by the surrounding gas. The eccentricity evolution depends strongly on the orbital rotation where prograde binaries are governed by gravitational torques form their circumbinary mini disc, with eccentricities being damped, while for retrograde binaries the eccentricities are excited to >∼ 0.9 by accretion torques. In two cases, retrograde binaries ultimately undergo a close periapsis passage which results in a merger via gravitational waves after only a few thousand binary orbits. Thus, the merger time-scale can be far shorter than the AGN disc lifetime. These simulations support an efficient AGN disc merger pathway for BHs. [ABSTRACT FROM AUTHOR]

Astrophysical models of binary-black hole mergers in the universe require a significant fraction of stellar-mass black holes (BHs) to receive negligible natal kicks to explain the gravitational wave detections. This implies that BHs should be retained even in open clusters with low escape velocities (≲1 km s−1). We search for signatures of the presence of BHs in the nearest open cluster to the Sun – the Hyades – by comparing density profiles of direct N -body models to data from Gaia. The observations are best reproduced by models with 2–3 BHs at present. Models that never possessed BHs have an half-mass radius |$\sim 30~{{\ \rm per\ cent}}$| smaller than the observed value, while those where the last BHs were ejected recently (≲150 Myr ago) can still reproduce the density profile. In 50  per cent of the models hosting BHs, we find BHs with stellar companion(s). Their period distribution peaks at ∼103 yr, making them unlikely to be found through velocity variations. We look for potential BH companions through large Gaia astrometric and spectroscopic errors, identifying 56 binary candidates – none of which is consistent with a massive compact companion. Models with 2–3 BHs have an elevated central velocity dispersion, but observations cannot yet discriminate. We conclude that the present-day structure of the Hyades requires a significant fraction of BHs to receive natal kicks smaller than the escape velocity of |$\sim 3 \, \mathrm{km \, s^{-1}}$| at the time of BH formation and that the nearest BHs to the Sun are in, or near, Hyades. [ABSTRACT FROM AUTHOR]

In the inner region of the disc of an active galactic nucleus (AGN), the collision of two white dwarfs (WDs) through Jacobi capture might be inevitable, leading to a Type Ia supernova (SN Ia) explosion. This transient event, influenced by the disc gas and the gravity of the supermassive black hole (SMBH), exhibits distinct characteristics compared with normal SNe Ia. The energy of the explosion is mainly stored in the ejecta in the form of kinetic energy. Typically, the ejecta is not decelerated effectively by the AGN disc and rushes rapidly out of the AGN disc. However, under the influence of the SMBH, most of the ejecta falls back toward the AGN disc. As the fallback ejecta becomes more dispersed, it interacts with the disc gas, converting its kinetic energy into thermal energy. This results in a high-energy transient characterized by a rapid initial rise followed by a decay with L ∝ t −2.8. The time-scale of the transient ranges from hours to weeks, depending on the mass of the SMBH. This process generates high-energy radiation spanning from hard X-rays to the soft γ range. Additionally, the subsequent damage to the disc may result in changing-look AGNs. Moreover, the falling back of SNe Ia ejecta on to the AGN disc significantly increases the metallicity of the AGN and can even generate heavy elements within AGN discs. [ABSTRACT FROM AUTHOR]

We measure precise orbits and dynamical masses and derive age constraints for six confirmed and one candidate Sirius-like systems, including the Hyades member HD 27483. Our orbital analysis incorporates radial velocities, relative astrometry, and Hipparcos – Gaia astrometric accelerations. We constrain the main-sequence lifetime of a white dwarf's progenitor from the remnant's dynamical mass and semi-empirical initial–final mass relations and infer the cooling age from mass and effective temperature. We present new relative astrometry of HD 27483 B from Keck/NIRC2 observations and archival Hubble Space Telescope data, and obtain the first dynamical mass of |${0.798}_{-0.041}^{+0.10}$| M⊙, and an age of |${450}_{-180}^{+570}$| Myr, consistent with previous age estimates of Hyades. We also measure precise dynamical masses for HD 114174 B (0.591 ± 0.011 M⊙) and HD 169889 B (⁠|${0.526}_{-0.037}^{+0.039}$| M⊙), but their age precisions are limited by their uncertain temperatures. For HD 27786 B, the unusually small mass of 0.443 ± 0.012 M⊙ suggests a history of rapid mass-loss, possibly due to binary interaction in its progenitor's asymtotic giant branch phase. The orbits of HD 118475 and HD 136138 from our radial velocity fitting are overall in good agreement with Gaia DR3 astrometric two-body solutions, despite moderate differences in the eccentricity and period of HD 136138. The mass of |${0.580}_{-0.039}^{+0.052}$| M⊙ for HD 118475 B and a speckle imaging non-detection confirms that the companion is a white dwarf. Our analysis shows examples of a rich number of precise WD dynamical mass measurements enabled by Gaia DR3 and later releases, which will improve empirical calibrations of the white dwarf initial–final mass relation. [ABSTRACT FROM AUTHOR]

With nearly a hundred gravitational wave detections, the origin of black hole mergers has become a key question. Here, we focus on understanding the typical galactic environment in which binary black hole (BBH) mergers arise. To this end, we synthesize progenitors of BBH mergers as a function of the redshift of progenitor formation, present-day formation galaxy mass, and progenitor stellar metallicity for 240 star formation and binary evolution models. We provide guidelines to infer the formation galaxy properties and time of formation, highlighting the interplay between the star formation rate and the efficiency of forming merging BBHs from binary stars, both of which strongly depend on metallicity. We find that across models, over 50 per cent of BBH mergers have a progenitor metallicity of a few tenths of Solar metallicity, however, inferring formation galaxy properties strongly depends on both the binary evolution model and global metallicity evolution. The numerous, low-mass black holes (≲ 15 M⊙) trace the bulk of the star formation in galaxies heavier than the Milky Way (M Gal ≳ 1010.5 M⊙). In contrast, heavier BBH mergers typically stem from larger black holes forming in lower metallicity dwarf galaxies (M Gal ≲ 109 M⊙). We find that the progenitors of detectable BBHs tend to arise from dwarf galaxies at a lower formation redshift (≲1). We also produce a posterior probability of the progenitor environment for any detected gravitational wave signal. For the massive GW150914 merger, we show that it likely came from a very low-metallicity (Z ≲ 0.025 Z⊙) environment. [ABSTRACT FROM AUTHOR]

Population-synthesis codes are an unique tool to explore the parameter space of massive binary star evolution and binary compact object (BCO) formation. Most population-synthesis codes are based on the same stellar evolution model, limiting our ability to explore the main uncertainties. Here, we present the new version of the code sevn , which overcomes this issue by interpolating the main stellar properties from a set of pre-computed evolutionary tracks. We describe the new interpolation and adaptive time-step algorithms of sevn , and the main upgrades on single and binary evolution. With sevn , we evolved 1.2 × 109 binaries in the metallicity range 0.0001 ≤ Z ≤ 0.03, exploring a number of models for electron-capture, core-collapse and pair-instability supernovae, different assumptions for common envelope, stability of mass transfer, quasi-homogeneous evolution, and stellar tides. We find that stellar evolution has a dramatic impact on the formation of single and BCOs. Just by slightly changing the overshooting parameter (λov = 0.4, 0.5) and the pair-instability model, the maximum mass of a black hole can vary from ≈60 to ≈100 M⊙. Furthermore, the formation channels of BCOs and the merger efficiency we obtain with sevn show significant differences with respect to the results of other population-synthesis codes, even when the same binary-evolution parameters are used. For example, the main traditional formation channel of BCOs is strongly suppressed in our models: at high metallicity (Z ≳ 0.01) only <20 per cent of the merging binary black holes and binary neutron stars form via this channel, while other authors found fractions >70 per cent. [ABSTRACT FROM AUTHOR]

We present high-angular-resolution observations of Sakurai's object using the Atacama Large Millimeter Array, shedding new light on its morpho-kinematical structure. The millimetre continuum emission observed at an angular resolution of 20 milliarcsec (corresponding to 70 AU) reveals a bright compact central component whose spectral index indicates that it is composed of amorphous carbon dust. Based on these findings, we conclude that this emission traces the previously suggested dust disc observed in mid-infrared observations, and therefore our observations provide the first direct imaging of this disc. The H12CN(J = 4 → 3) line emission observed at an angular resolution of 300 milliarcsec (corresponding to 1000 AU) displays a bipolar structure with a north–south velocity gradient. From the position–velocity diagram of this emission, we identify the presence of an expanding disc and a bipolar molecular outflow. The inclination of the disc is determined to be i = 72°. The derived values for the de-projected expansion velocity and the radius of the disc are vexp = 53 km s−1 and R = 277 AU, respectively. On the other hand, the de-projected expansion velocity of the bipolar outflow detected in the H12CN(J = 4 → 3) emission is of approximately 1000 km s−1. We propose that the molecular outflow has an hourglass morphology with an opening angle of around 60°. Our observations unambiguously show that an equatorial disc and bipolar outflows formed in Sakurai's object during the 30 years following the occurrence of the born-again event, providing important constraints for future modelling efforts of this phenomenon. [ABSTRACT FROM AUTHOR]

Aims. We aim to compute the binary fraction of "classical" dwarf spheroidal galaxies (dSphs) that are satellites of the Milky Way (MW). This value can offer insights into the binary fraction in environments that are less dense and more metal-poor than our own galaxy. Additionally, knowledge of the binary fraction in dwarf galaxies is important with respect to avoiding overestimations of their dark matter content, inferred from stellar kinematics. Methods. We refined an existing method from the literature, placing an emphasis on providing robust uncertainties on the value of the binary fraction. We applied this modified method to a VLT/FLAMES dataset for Sculptor, specifically acquired for the purpose of velocity monitoring of individual stars, as well as to literature datasets for other six MW "classical" dSphs. In all cases, the targeted stars were mainly red giant branch stars, with expected masses of around 0.8 M⊙. The VLT/FLAMES dataset offers the most precise binary fractions compared to literature datasets, due to its time baseline of 12 yr, along with at least nine repeated observations for each star. Results. We found that the binary fraction of Sculptor is 0.55−0.19+0.17. We find that it is important to take into account the Roche lobe overflow for constraining the period distribution of binary stars. In contrast to what has recently been proposed in the literature, our analysis indicates that there is no evidence to support varying the properties of the binary stellar population or their deviations from those established for the solar neighborhood, based on the sample of MW dSphs analyzed here. [ABSTRACT FROM AUTHOR]

We report the discovery of the first hot subdwarf B (sdB) star with a massive compact companion in a wide (P = 892.5 ± 60.2 d) binary system. It was discovered based on an astrometric binary solution provided by the Gaia mission Data Release 3. We performed detailed analyses of the spectral energy distribution (SED) as well as spectroscopic follow-up observations and confirm the nature of the visible component as a sdB star. The companion is invisible despite of its high mass of Mcomp = 1.50−0.45+0.37 M⊙ M comp = 1. 50 − 0.45 + 0.37 M ⊙ $ M_{\mathrm{comp}}=1.50_{-0.45}^{+0.37}\,M_{\odot} $. A main sequence star of this mass would significantly contribute to the SED and can be excluded. The companion must be a compact object, either a massive white dwarf or a neutron star. Stable Roche lobe overflow to the companion likely led to the stripping of a red giant and the formation of the sdB, the hot and exposed helium core of the giant. Based on very preliminary data, we estimate that ∼9% of the sdBs might be formed through this new channel. This binary might also be the prototype for a new progenitor class of supernovae type Ia, which has been predicted by theory. [ABSTRACT FROM AUTHOR]

We report the analysis of circumbinary (CB) discs formed in a radiation hydrodynamical simulation of star cluster formation. We consider both pure binary stars and pairs within triple and quadruple systems. The protostellar systems are all young (ages < 105 yrs). We find that the systems that host a CB disc have a median separation of ≈11 au, and the median characteristic radius of the discs is ≈64 au. We find that 89 per cent of pure binaries with semimajor axes a < 1 au have a CB disc, and the occurrence rate of CB discs is bimodal with log-separation in pure binaries with a second peak at a ≈ 50 au. Systems with a > 100 au almost never have a CB disc. The median size of a CB disc is between ≈5 and 6  a depending on the order of the system, with higher order systems having larger discs relative to binary separation. We find the underlying distributions of mutual inclination between CB discs and binary orbits from the simulation are in good agreement with those of observed CB discs. [ABSTRACT FROM AUTHOR]

We perform population synthesis of massive binaries to study the mergers of neutron stars (NSs) and black holes (BHs) with the cores of their giant secondaries during common envelope evolution (CEE). We use different values of the efficiency parameter αCE in the framework of the energy formalism for traditional CEE (αCE ≤ 1) and including additional energy sources to unbind the envelope (αCE > 1). We constrain the possible values of αCE by comparing the results of our simulations with local rate densities of binary compact object mergers as inferred from gravitational-wave observations. We find two main evolutionary pathways of binary systems that result in NS–core mergers, while only one of them can also lead to the merger of a BH with the core of the giant star. We explore the zero-age main-sequence statistical properties of systems that result in NS/BH–core mergers and find that the two evolutionary channels correspond to a bimodal distribution of orbital separations. We estimate the percentage of the mergers' event rates relative to core-collapse supernovae. We include the effect of mass accreted by the NS/BH during CEE in a separate set of simulations and find that it does not affect the mergers' event rates. [ABSTRACT FROM AUTHOR]

In this paper, we study how gaseous dynamical friction (DF) affects the motion of fly-by stellar-mass black holes (sBHs) embedded in active galactic nucleus (AGN) discs. We perform three-body integrations of the interaction of two co-planar sBHs in nearby, initially circular orbits around the supermassive black hole. We find that DF can facilitate the formation of gravitationally bound near-Keplerian binaries in AGN discs, and we delineate the discrete ranges of impact parameters and AGN disc parameters for which such captures occur. We also report trends in the bound binaries' eccentricity and sense of rotation (prograde or retrograde with respect to the background AGN disc) as a function of the impact parameter of the initial encounter. While based on an approximate description of gaseous friction, our results suggest that binary formation in AGN discs should be common and may produce both prograde and retrograde, as well as both circular and eccentric binaries. [ABSTRACT FROM AUTHOR]

Numerous circumbinary planets have been discovered in surveys of transiting planets. Often, these planets are found to orbit near to the zone of dynamical instability, close to the central binary. The existence of these planets has been explained by hydrodynamical simulations that show that migrating circumbinary planets, embedded in circumbinary discs, halt at the central cavity that is formed by the central binary. Transit surveys are naturally most sensitive to finding circumbinary planets with the shortest orbital periods. The future promise of detecting longer period systems using radial-velocity searches, combined with the anticipated detection of numerous circumbinary planets by ESA's PLATO mission, points to the need to model and understand the formation and evolution of circumbinary planets in a more general sense than has been considered before. With this goal in mind, we present a newly developed global model of circumbinary planet formation that is based on the mercury6 symplectic N -body integrator, combined with a model for the circumbinary disc and prescriptions for a range of processes involved in planet formation such as pebble accretion, gas envelope accretion, and migration. Our results show that under reasonable assumptions, the pebble accretion scenario can produce circumbinary systems that are similar to those observed, and in particular is able to produce planets akin to Kepler-16b and Kepler-34b. Comparing our results to other systems, we find that our models also adequately reproduce such systems, including multiplanet systems. Resonances between neighbouring planets are frequently obtained, whilst ejections of planets by the central binary acts as an effective source of free floating planets. [ABSTRACT FROM AUTHOR]

Low-mass star formation regions are unlikely to fully populate their initial mass functions (IMFs), leading to a deficit of massive stars. In binary stellar populations, the full range of binary separations and mass ratios will also be underpopulated. To explore the effects of stochastic sampling in the integrated light of stellar clusters, we calculate models at a broad range of cluster masses, from 102 to 107 M⊙, using a binary stellar population synthesis code. For clusters with stellar masses less than 105 M⊙, observable quantities show substantial scatter and their mean properties reflect the expected deficit of massive stars. In common with previous work, we find that purely stochastic sampling of the IMF appears to underestimate the mass of the most massive star in known clusters. However, even with this constraint, the majority of clusters likely inject sufficient kinetic energy to clear their birth clusters of gas. For quantities that directly measure the impact of the most massive stars, such as N ion, ξion, and βUV, uncertainties due to stochastic sampling dominate over those from the IMF shape or distribution of binary parameters, while stochastic sampling has a negligible effect on the stellar continuum luminosity density. [ABSTRACT FROM AUTHOR]

Superorbital periods are observed in the optical light curves of many Be/X-ray binaries yet their origin has remained somewhat elusive. We suggest that precession of the spin axis of the Be star can drive superorbital periods, particularly for short orbital period binaries. We consider the short orbital period (⁠|$P_{\rm orb}=16.6\, \rm d$|⁠) and highly eccentric (e b = 0.72) Be/X-ray binary A0538−66 that has a superorbital period of |$421\, \rm d$|⁠. First, we show that the spin axis precession time-scale is about twice the observed superorbital period. Then, with hydrodynamic simulations we show that the Be star decretion disc can remain locked to the equator of the precessing Be star. At each periastron passage of the neutron star, material is accreted into a disc around the neutron star. The neutron star disc nodally precesses on the same time-scale as the Be star disc and therefore both discs can contribute to the observed superorbital period. For wider and less eccentric binary systems, the Be star disc can have a larger radial extent and more complex behaviour is expected as a result of disc warping and breaking. [ABSTRACT FROM AUTHOR]

The ground-based gravitational wave (GW) observatories discover a population of merging stellar binary black holes (BBHs), which are promising targets for multiband observations by the low-, middle-, and high-frequency GW detectors. In this paper, we investigate the multiband GW detections of BBHs and demonstrate the advantages of such observations in improving the localization and parameter estimates of the sources. We generate mock samples of BBHs by considering different formation models as well as the merger rate density constrained by the current observations (GWTC-3). We specifically consider the astrodynamical middle-frequency interferometer GW observatory (AMIGO) in the middle-frequency band and estimate that it may detect 21–91 BBHs with signal-to-noise ratio ϱ ≥ 8 in a 4-yr observation period. The multiband observations by the low-frequency detectors [Laser Interferometer Space Antenna (LISA) and Taiji] and AMIGO may detect 5–33 BBHs with ϱLT ≥ 5 and ϱAMI ≥ 5, which can evolve to the high-frequency band within 4 yr and can be detected by the Cosmic Explorer (CE) and Einstein Telescope (ET). The joint observations of LISA-Taiji-AMIGO-ET-CE may localize the majority of the detectable BBHs in sky areas of 7 × 10−7 to 2 × 10−3 deg2, which is improved by a factor of ∼120, ∼2.4 × 105, ∼1.8 × 104, or ∼1.2 × 104, comparing with those by only adopting CE-ET, AMIGO, LISA-Taiji, or LISA-Taiji-AMIGO. These joint observations can also lead to an improvement of the measurement precision of the chirp mass (symmetric mass ratio) by a factor of ∼ 5.5 × 104 (33), ∼16 (8), ∼120 (90), or ∼5 (5), comparing with those by CE-ET, AMIGO, LISA-Taiji, or LISA-Taiji-AMIGO. [ABSTRACT FROM AUTHOR]

Disintegrating multiple systems have been previously discovered from kinematic studies of the Hipparcos catalogue. They are presumably the result of dynamical encounters taking place in the Galactic disc between single/multiple systems. In this paper, we aim to expand the search for such systems, to study their properties, as well as to characterize possible low-mass ejecta (i.e. brown dwarfs and planets). We have assembled a list of 15 candidate systems using astrometry from the Tycho-Gaia astrometric solution (later upgraded with Gaia DR3), and here we present the discovery and follow-up of five of them. We have obtained DECam imaging for all five systems and by combining near-infrared photometry and proper motion, we searched for ultracool ejected components. We find that the system consisting of TYC 7731-1951-1, TYC 7731-2128 AB, and TYC 7731-1995-1ABC?, contains one very promising ultracool dwarf candidate. Using additional data from the literature, we have found that three out of five disintegrating system candidates are likely to be true disintegrating systems. [ABSTRACT FROM AUTHOR]

We use the rapid binary stellar evolution code binary_c to estimate the rate of merging neutron stars with numerous combinations of envelope ejection efficiency and natal kick dispersion. We find a peak in the local rate of merging neutron stars around α ≈ 0.3–0.4, depending on the metallicity, where α is the efficiency of utilizing orbital energy to unbind the envelope. The peak height decreases with increasing electron-capture supernova kick dispersion σECSN. We explain the peak as a competition between the total number of systems that survive the common-envelope phase increasing with α and their separation, which increases with α as well. Increasing α reduces the fraction of systems that merge within a time shorter than the age of the Universe and results in different mass distributions for merging and non-merging double neutron stars. This offers a possible explanation for the discrepancy between the Galactic double neutron star mass distribution and the observed massive merging neutron star event GW190425. Within the α–σECSN parameter space that we investigate, the rate of merging neutron stars spans several orders of magnitude up to more than |$1\times 10^{3} \, \mathrm{Gpc}^{-3}\, \mathrm{yr}^{-1}$| and can be higher than the observed upper limit or lower than the observed lower limit inferred thus far from merging neutron stars detected by gravitational waves. Our results stress the importance of common-envelope physics for the quantitative prediction and interpretation of merging binary neutron star events in this new age of gravitational wave astronomy. [ABSTRACT FROM AUTHOR]

We present a homogeneously selected sample of 15 779 candidate binary systems with main sequence primary stars and orbital periods shorter than 5 d. The targets were selected from TESS full-frame image light curves on the basis of their tidally induced ellipsoidal modulation. Spectroscopic follow-up suggests a sample purity of 83 ± 13 per cent. Injection-recovery tests allow us to estimate our overall completeness as 28 ± 3 per cent with P orb < 3 d and to quantify our selection effects. 39 ± 4 per cent of our sample are contact binary systems, and we disentangle the period distributions of the contact and detached binaries. We derive the orbital period distribution of the main-sequence binary population at short orbital periods, finding a distribution continuous with the lognormal distribution previously found for solar-type stars at longer periods, but with a significant steepening at P orb ≲ 3 d, and a pile-up of contact binaries at P orb  ≈ 0.4 d. Companions in the period range of 1–5 d are an order of magnitude more frequent around stars hotter than |$\approx 6250\, \rm K$| (the Kraft break) when compared to cooler stars, suggesting that magnetic braking shortens the lifetime of cooler binary systems. However, the period distribution in the range 1–10 d is independent of temperature. We detect resolved tertiary companions to 9.0 ± 0.2 per cent of our binaries with a median separation of 3200 au. The frequency of tertiary companions rises to 29 ± 5 per cent among the systems with the shortest ellipsoidal periods. This large binary sample with quantified selection effects will be a powerful resource for future studies of detached and contact binary systems with P orb<5 d. [ABSTRACT FROM AUTHOR]

The shrinking of a binary orbit driven by the interaction with a gaseous circumbinary disc, initially advocated as a potential way to catalyse the binary merger, has recently been debated in the case of geometrically thick (i.e. with H / R ≳ 0.1) discs. However, a clear consensus is still missing mainly owing to numerical limitations, such as fixed orbit binaries or lack of resolution inside the cavity carved by the binary in its circumbinary disc. In this work, we assess the importance of evolving the binary orbit by means of hydrodynamic simulations performed with the code gizmo in meshless finite mass mode. In order to model the interaction between equal mass circular binaries and their locally isothermal circumbinary discs, we enforce hyper-Lagrangian resolution inside the cavity. We find that fixing the binary orbit ultimately leads to an overestimate of the gravitational torque that the gas exerts on the binary and an underestimate of the torque due to the accretion of material on to the binary components. Furthermore, we find that the modulation of the accretion rate on the binary orbital period is strongly suppressed in the fixed orbit simulation, while it is clearly present in the live binary simulations. This has potential implications for the prediction of the observable periodicities in massive black hole binary candidates. [ABSTRACT FROM AUTHOR]

We model Pop III star formation in different FUV and X-ray backgrounds, including radiation feedback from protostars. We confirm previous results that a moderate X-ray background increases the number of Pop III systems per unit cosmological volume, but masses and multiplicities of the system are reduced. The stellar mass function also agrees with previous results, and we confirm the outward migration of the stars within the protostellar discs. We find that nearly all Pop III star systems are hierarchical, i.e. binaries of binaries. Typically, two equal-mass stars form near the centre of the protostellar disc and migrate outwards. Around these stars, mini-discs fragment forming binaries that also migrate outwards. Stars may also form at Lagrange points L4/L5 of the system. Afterwards, star formation becomes more stochastic due to the large multiplicity, and zero-metallicity low-mass stars can form when rapidly ejected from the disc. Stars in the disc often have eccentric orbits, leading to a periodic modulation of their accretion rates and luminosities. At the pericentre, due to strong accretion, the star can enter a red-supergiant phase reaching nearly Eddington luminosity in the optical bands (m AB ∼ 34 for a 100 M⊙ star at z = 6). During this phase, the star, rather than its nebular lines, can be observed directly by JWST , if sufficiently magnified by a gravitational lens. The ∼10 000 AU separations and high eccentricities of many Pop III star binaries in our simulations are favourable parameters for IMBH mergers – and gravitational waves emission – through orbital excitation by field stars. [ABSTRACT FROM AUTHOR]