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Millisecond pulsars with white dwarf companions have typical eccentricities |$e\sim 10^{-6}{\!-\!}10^{-3}$|⁠. The eccentricities of helium white dwarfs are explained well by applying the fluctuation–dissipation theorem to convective eddies in their red giant progenitors. We extend this theory to more massive carbon–oxygen (CO) white dwarfs with asymptotic giant branch (AGB) progenitors. Due to the radiation pressure in AGB stars, the dominant factor in determining the remnant white dwarf's eccentricity is the critical residual hydrogen envelope mass |$m_{\rm env}$| required to inflate the star to giant proportions. Using a suite of mesa stellar evolution simulations with |$\Delta m_{\rm c}=10^{-3}\, {\rm M}_{\odot }$| core-mass intervals, we resolved the AGB thermal pulses and found that the critical |$m_{\rm env}\propto m_{\rm c}^{-6}$|⁠. The resulting eccentricity |$e\sim 3\times 10^{-3}$| is almost independent of the remnant CO white dwarf's mass |$m_{\rm c}$|⁠. Nearly all of the measured eccentricities lie below this robust theoretical limit, indicating that the eccentricity is damped during the common-envelope inspiral that follows the unstable Roche lobe overflow of the AGB star. Specifically, we focused on white dwarfs with median masses |$m_{\rm c}\gt 0.6\, {\rm M}_{\odot }$|⁠. These massive white dwarfs begin their inspiral with practically identical orbital periods and eccentricities, eliminating any dependence on the initial conditions. For this sub-sample, we find an empirical relation |$e\propto P^{3/2}$| between the final period and eccentricity that is much tighter than previous studies – motivating theoretical work on the eccentricity evolution during the common envelope phase. The eccentricities of lower mass CO white dwarfs may be explained by alternative formation channels. [ABSTRACT FROM AUTHOR]

Cen X-3 is a compact, high-mass X-ray binary (HMXRB), likely powered by Roche lobe overflow. We present a phase-resolved X-ray spectral and timing analysis of a target of opportunity Chandra observation made during a low-flux to high-flux transition. The high-resolution spectra allow us to delve into the events that occurred during this episode. The spectrum is described by a single black body absorbed by a local column density of the order of 1023 − 24 cm−2, which is one to two orders of magnitude higher than found for previous analyses of data taken at similar orbital phases. Such a large column produces a Compton shoulder in the Fe Kα line. The transition appears to be caused by the onset of efficient cooling, which cools the plasma by 10 million degrees in just 10 ks, allowing matter to enter the magnetosphere. This happens after a major disturbance, probably the arrival of a train of wind clumps with individual masses in the range 1019 − 20 g. This train moves ballistically in an eccentric orbit around the NS, producing a distinctive Doppler modulation in the Fe XXV line. [ABSTRACT FROM AUTHOR]

Context. Supersoft X-ray sources (SSSs) have been proposed as one of the progenitors for Type Ia supernovae. However, the exact origin of the quasi-periodic variability in the optical light curve remains a mystery. Aims. In this work, our goal is to investigate the effect of the feedback of an evolved main-sequence companion star on X-ray irradiation and find whether periodic X-ray irradiation of the companion star could reproduce periodic mass transfer. Methods. Using the Modules for Experiments in Stellar Astrophysics (MESA) code, we modeled the evolutionary track of the companion star under the influence of supersoft X-ray irradiation, and we calculated the resulting mass transfer rate. Results. We find that the supersoft X-ray heating of the companion star can result in the expansion of the companion, causing it to greatly overflow its Roche lobe and thereby increasing the mass transfer rate. The periodic X-ray irradiation on the companion stars leads to periodic changes in the mass transfer rate. For a given companion star, higher irradiation efficiencies result in a higher mass transfer rate. Additionally, the mass transfer rate increases as the mass of the companion star decreases for a given irradiation efficiency. Conclusions. The companion star undergoing thermal timescale mass transfer is periodically irradiated by the X-rays from the WD, which can lead to periodic enhancement of the mass transfer rate. The mechanism could be the origin of the quasi-periodic optical light curve in supersoft X-ray sources. [ABSTRACT FROM AUTHOR]

The precessing jets of microquasar SS 433 have punched through the supernova remnant W 50 from the explosion forming the compact object. The jets collimate before reaching beyond the shell, some 40 pc downstream, just the region of origin of TeV gamma radiation. Collimation could be effected by ambient pressure in the SNR cavity; I investigate conditions under which the W 50 morphology and the sites of TeV gamma radiation can be explained in terms of collimation, with associated shocks, induced by ambient pressure. The SNR is now ~ 10 5 years after the supernova; with the present pressure, collimation and associated shocks would indeed occur ~40 pc downstream. Modeling of the evolution of binary systems indicates that the Roche lobe overflow and the initiation of the jets may be recent rather than early; present day collimation would still occur ~40 pc downstream, but the cone angle of the precession must then have increased with time—driven by the Roche lobe overflow. The morphology of W 50 and the site of the origin of TeV radiation are readily explained in terms of the collimation of the jets by internal SNR pressure. [ABSTRACT FROM AUTHOR]

Ultra-hot Jupiter Kelt9b impels to reconsider existing models of the upper atmospheres of hot exoplanets, which were previously developed using examples of G or M star systems such as HD209458b and GJ436b. The unique conditions of interaction between the radiation of an A-class star and the atmosphere necessitate kinetic modeling of excited levels of elements, primarily the hydrogen atom. Kelt9b shows the absorption for several Balmer lines and lines of a number of heavy elements, the quantitative interpretation of which is an urgent problem. In this study, for the first time, 3D modeling of the atmosphere of a planet with a close location of the Roche lobe is implemented with allowance for the aeronomy and kinetics of excited hydrogen. [ABSTRACT FROM AUTHOR]

Flaring in the SS 433 microquasar is dominated by outbursts from material at distances from the centre of mass of the binary system comparable to the separation of the two components. This note completes a demonstration that ejected plasma leaves the system in the region of the L2 point, there overflowing the outer Roche lobe and giving rise to a spiral structure as it leaves the system as part of the local environment. It also provides a new measure of the mass ratio of the binary. [ABSTRACT FROM AUTHOR]

Context. The vast majority of close binaries containing a compact object, including the progenitors of supernovae Ia and at least a substantial fraction of all accreting black holes in the Galaxy, form through common-envelope (CE) evolution. Despite this importance, we struggle to even understand the energy budget of CE evolution. For decades, observed long-period post-CE binaries have been interpreted as evidence of additional energies contributing during CE evolution. We have recently shown that this argument is based on simplified assumptions for all long-period post-CE binaries containing massive white dwarfs (WDs). The only remaining post-CE binary star that has been claimed to require contributions from additional energy sources to understand its formation is KOI 3278. Aims. Here, we address in detail the potential evolutionary history of KOI 3278. In particular, we investigate whether extra energy sources, such as recombination energy, are indeed required to explain its existence. Methods. We used the 1D stellar evolution code MESA to carry out binary evolution simulations and searched for potential formation pathways for KOI 3278 that are able to explain its observed properties. Results. We find that KOI 3278 can be explained if the WD progenitor filled its Roche lobe during a helium shell flash. In this case, the orbital period of KOI 3278 can be reproduced if the CE binding energy is calculated taking into account gravitational energy and thermodynamic internal energy. While the CE evolution that led to the formation of KOI 3278 must have been efficient – that is, most of the available orbital energy must have been used to unbind the CE – recombination energy is not required. Conclusions. We conclude that currently not a single observed post-CE binary requires one to assume that energy sources other than gravitational and thermodynamic energy are contributing to CE evolution. KOI 3278, however, remains an intriguing post-CE binary as, unlike its siblings, understanding its existence requires highly efficient CE ejection. [ABSTRACT FROM AUTHOR]

We reported the light curves (LCs) and orbital period variations of four short-period eclipsing binaries in the Southern hemisphere. From short-cadence time-series observations of the TESS, the intrinsic light changes rapidly with time. Δ m max and Δ m min exhibit random wave-like variations or quasi-periodicities. We deduced 14 sets of photometric solutions from the truncated LCs using the W-D programme. The results imply that V757 Cen and BC Gru are near-contact binaries, whose one or two components almost fill the Roche lobes with |$f\gt 98{{\ \rm per\ cent}}$|⁠. Meanwhile, V535 Ara and AQ Tuc are A-subtype contact binaries. The asymmetric LCs were modelled by a cool spot assumed on a more massive component, which was used to track the stellar longitudes of star-spots. Based on all available eclipsing times (ETs), including 1495 ones from TESS LCs, the orbital period variations of four binaries were analysed. The (O − C) curves are coincidentally demonstrated by the light-time effect via the presence of the third bodies. The modulation periods approximate to 50 ∼ 60 yr. In the coplanar orbit with the central binaries, the third companions' masses are 0.105 M⊙ for V757 Cen, 0.340 M⊙ for BC Gru, 0.238 M⊙ for V535 Ara, and 0.343 M⊙ for AQ Tuc, whose systems are stable according to Harrington's criterion. Therefore, the four short-period eclipsing binaries, V757 Cen, BC Gru, V535 Ara, and AQ Tuc are hierarchical triple stellar systems. [ABSTRACT FROM AUTHOR]

We present high‐resolution (0.06 Å px −1$$ {}^{-1} $$) spectroscopic observations of the recurrent nova T Coronae Borealis obtained during the last 1.5 years (September 2022–January 2024), with the 2.0‐m RCC telescope of the Rozhen National Astronomical Observatory, Bulgaria. Double‐peaked emission is visible in the Hα$$ {H}_{\alpha } $$ line after the end of the superactive state. We subtract the red giant contribution and measure the distance between the peaks (Δva$$ \Delta {v}_a $$) of the line. For the period July 2023–January 2024, we find that Δva$$ \Delta {v}_a $$ is in range 90<Δva<120$$ 90<\Delta {v}_a<120 $$ km s −1$$ {}^{-1} $$. Assuming that the emission is from the accretion disc around the white dwarf, we find average radius of the accretion disc Rdisc=89±19$$ {R}_{\mathrm{disc}}=89\pm 19 $$ R ⊙$$ {}_{\odot } $$, which is approximately equal to the Roche lobe size of the white dwarf. Our results indicate that tidal torque plays an important role but that the disc can extend up to the Roche lobe of the accreting star. [ABSTRACT FROM AUTHOR]

With three-dimensional hydrodynamical simulations we show that the size of the decretion disc and the structure of the accretion flow on to the neutron star in a Be/X-ray binary strongly depends upon the disc aspect ratio, H / R. We simulate a Be star disc that is coplanar to the orbit of a circularly or moderately eccentric neutron star companion, thereby maximizing the effects of tidal truncation. For low-disc aspect ratio, H / R ≲ 0.1, the disc is efficiently tidally truncated by the neutron star. Most material that escapes the Roche lobe of the Be star is accreted by the neutron star through tidal streams. For larger disc aspect ratio, the outflow rate through the Be star disc is higher, tidal truncation becomes inefficient, the disc fills the Roche lobe and extends to the orbit of the companion. Some material escapes the binary as a gas stream that begins near the L2 point. While the accretion rate on to the neutron star is higher, the fraction of the outflow that is accreted by the neutron star is smaller. Low-density Be star discs are expected to be approximately isothermal, such that H / R increases with radius. Tidal truncation is therefore weaker for larger separation binaries, and lower mass primaries. [ABSTRACT FROM AUTHOR]

Many previous works studied the dynamical time-scale mass transfer stability criteria based on the donor response with neglecting the stellar structure of the accretor. In this letter, we investigate the radial response of accretors with mass accumulation and its effect on the binary mass transfer stability. We perform a series of detailed stellar evolution simulations with different types of accretors and obtain the radial variations of stars accreting at different rates. Since the time within which the donor loses half of the original mass has a correlation with the donor mass, we approximately obtain the mean mass transfer rate as a function of mass ratio. Assuming that the common envelope (CE) phase occurs if the accretor radius exceeds the outer Roche lobe radius, we obtain the critical mass ratio of dynamically unstable mass transfer. We find the critical mass ratios for donors filling their Roche lobes at the Main Sequence (MS) and Hertzsprung Gap (HG) stages are smaller than that derived from the radial response of the donor in the traditional way. Our results may suggest that the binary is easier to enter into the CE phase for a donor star at the MS or HG stage than previously believed. [ABSTRACT FROM AUTHOR]

The article is devoted to the analysis of the evolutionary status of the X-ray binary stars of the Galaxy. It is shown that the assumption of the conservative evolution of these binary systems leads to an overestimation of the X-ray luminosity of the Galaxy by 3–4 orders. The total observed rate of accretion of matter by relativistic components of X-ray binaries is close to yr, while the theoretically possible rate reaches yr. The contradiction between these estimates is eliminated if two factors are taken into account. The first of them is the formation of a common envelope in massive X-ray binary systems after filling the Roche lobe by the donor and the brief phase of a bright X-ray source. The common envelope eliminates the output of X-ray radiation generated during accretion, and also leads to the loss of part of the donor's matter from the system. The second factor is the presence of intense stellar wind of donors in massive X-ray binary, as well as the occurrence of induced stellar wind in low-mass donors due to exposure to hard radiation from an accreting relativistic star. At the same time, the generally accepted assumption that donors of X-ray binaries fill their Roche lobes may not be fulfilled. A significant part of the donor's wind matter may be lost from the system. In addition, radiation can enhance the stellar wind of the accretion disk, and part of this wind will also leave the system. There are other factors that reduce the total number of accreted matter: supernova explosions in X-ray binaries, destroying part of these systems, the impossibility of accretion onto rapidly rotating young neutron stars with a strong magnetic field, as well as a rapid drop in the rate of loss of matter by the donor as its mass decreases, characteristic for low-mass X-ray systems. [ABSTRACT FROM AUTHOR]

Post-common envelope binaries (PCEBs) containing a white dwarf (WD) and a main-sequence (MS) star can constrain the physics of common envelope evolution and calibrate binary evolution models. Most PCEBs studied to date have short orbital periods (P orb ≲ 1 d), implying relatively inefficient harnessing of binaries' orbital energy for envelope expulsion. Here, we present follow-up observations of five binaries from 3rd data release of Gaia mission containing solar-type MS stars and probable ultramassive WDs (⁠|$M\gtrsim 1.2\ {\rm M}_{\odot}$|⁠) with significantly wider orbits than previously known PCEBs, P orb = 18–49 d. The WD masses are much higher than expected for systems formed via stable mass transfer at these periods, and their near-circular orbits suggest partial tidal circularization when the WD progenitors were giants. These properties strongly suggest that the binaries are PCEBs. Forming PCEBs at such wide separations requires highly efficient envelope ejection, and we find that the observed periods can only be explained if a significant fraction of the energy released when the envelope recombines goes into ejecting it. Our one-dimensional stellar models including recombination energy confirm prior predictions that a wide range of PCEB orbital periods, extending up to months or years, can potentially result from Roche lobe overflow of a luminous asymptotic giant branch (AGB) star. This evolutionary scenario may also explain the formation of several wide WD + MS binaries discovered via self-lensing, as well as a significant fraction of post-AGB binaries and barium stars. [ABSTRACT FROM AUTHOR]

Very-faint X-ray binaries (VFXBs) are a subclass of black holes and neutron stars in binaries that appear to be accreting at a very low rate. In addition to providing interesting constraints on poorly understood forms of accretion, elucidating the nature of VFXBs is particularly interesting for binary evolution and population modelling. Through near-infrared (NIR) spectroscopy, we here investigate the nature of the bursting neutron star and VFXB 1RXH J173523.7−354013 (J1735), which persistently accretes at an X-ray luminosity of L X ∼ 1034–1035 ergs−1. Our analysis shows that the NIR emission is dominated by that of the companion star, which we find to be a late G or early K-type giant, making this the second neutron star identified as a VFXB found to have a giant companion. We discuss how several of the system properties are difficult to reconcile with a wind-fed symbiotic X-ray binary. We therefore also propose an alternative scenario wherein J1735 is a wide binary system (supported by the discovery of a 7.5 d modulation in the NIR light curves) with a quiescent luminosity of L X ∼ 1034–1035 ergs−1, in which the donor star is overflowing its Roche lobe. This raises the possibility that J1735 may, every century or more, exhibit very long and very bright outbursts during which it reaches accretion rates around the Eddington limit like the neutron star Z sources. [ABSTRACT FROM AUTHOR]

An unidentified γ-ray source 4FGL J1838.2+3223 has been proposed as a pulsar candidate. We present optical time-series multiband photometry of its likely optical companion obtained with the 2.1-m telescope of Observatorio Astronómico Nacional San Pedro Mártir, Mexico. The observations and the data from the Zwicky Transient Facility revealed the source brightness variability with a period of ≈4.02 h likely associated with the orbital motion of the binary system. The folded light curves have a single sine-like peak per period with an amplitude of about three magnitudes accompanied by fast sporadic flares up to one magnitude level. We reproduce them modelling the companion heating by the pulsar. As a result, the companion side facing the pulsar is strongly heated up to 11300 ± 400 K, while the temperature of its back side is only 2300 ± 700 K. It has a mass of 0.10 ± 0.05 M⊙ and underfills its Roche lobe with a filling factor of |$0.60^{+0.10}_{-0.06}$|⁠. This implies that 4FGL J1838.2+3223 likely belongs to the 'spider' pulsar family. The estimated distance of ≈3.1 kpc is compatible with Gaia results. We detect a flare from the source in X-rays and ultraviolet using Swift archival data and another one in X-rays in the eROSITA all-sky survey. Both flares have X-ray luminosity of ∼1034 erg s−1 which is two orders of magnitude higher than the upper limit in quiescence obtained from eROSITA assuming spectral shape typical for spider pulsars. If the spider interpretation is correct, these flares are among the strongest observed from non-accreting spider pulsars. [ABSTRACT FROM AUTHOR]

Contact binaries are close binary systems in which both components fill their inner Roche lobes so that the stars are in direct contact, and in potential mass and energy exchange. The most common such systems of low mass are the so-called W UMa-type. In the last few years, there has been a growing interest of the astronomical community in stellar mergers, primarily due to the detection of gravitational waves (mergers of black holes and neutron stars), but also because of an alternative model for the type Ia supernovae (merger of two white dwarfs), which are again particularly important in cosmology where they played a significant role in the discovery of dark energy and the accelerated expansion of the Universe. In that sense, contact systems of W UMa type with extremely low mass ratio are especially interesting because there are indications that, in their case too, stars can merge and possibly form fast-rotating stars such as FC Com stars and the blue-stragglers, and (luminous) red novae such as V1309 Sco. Namely, the previous theoretical research has shown that in the cases when the orbital angular momentum of the system is only about three times larger than the rotational angular momentum of the primary, a tidal Darwin's instability occurs, the components can no longer remain in synchronous rotation, orbit continue to shrink fast, and they finally merge into a single star. The above stability condition for contact systems can be linked to a specific critical mass ratio below which we expect a system to be unstable. We give an overview of this condition and show how it can be used to identify potential mergers. Finally, we discuss a number of known extreme mass ratio binaries from the literature and consider prospects for future research on this topic. [ABSTRACT FROM AUTHOR]

We present evidence for a 0.278(8) d ( =6.7 h) orbital period in the X-ray transient GRS 1716-249 (=N Oph 93), based on a superhump modulation detected during the 1995 mini-outburst plus ellipsoidal variability in quiescence. With a quiescent magnitude of r  = 23.19 ± 0.15 N Oph 93 is too faint to warrant a full dynamical study through dedicated time-resolved spectroscopy. Instead, we apply the FWHM– K 2 correlation to the disc H α emission line detected in Gran Telescopio Canarias spectra and obtain K 2 = 521 ± 52 km s−1. This leads to a mass function f (M) = 4.1 ± 1.2 M⊙, thus indicating the presence of a black hole in this historic X-ray transient. Furthermore, from the depth of the H α trough and the quiescent light curve we constrain the binary inclination to i  = 61 ± 15°, while the detection of superhumps sets an upper limit to the donor to compact star mass ratio q  = M 2/ M 1 ≲ 0.25. Our de-reddened (r − i) colour is consistent with a ≈ K6 main sequence star that fills its Roche lobe in a 0.278 d orbit. Using all this information we derive a compact object mass |$M_{1}=6.4^{+3.2}_{-2.0}$| M⊙ at 68 per cent confidence. We also constrain the distance to GRS 1716-249 to 6.9 ± 1.1 kpc, placing the binary ∼0.8 kpc above the Galactic Plane, in support of a large natal kick. [ABSTRACT FROM AUTHOR]

In this paper, we study compact binary millisecond pulsars with low- and very low-mass companion stars (spiders) in the Galactic field, using data from the latest Gaia data release (DR3). We infer the parallax distances of the optical counterparts to spiders, which we use to estimate optical and X-ray luminosities. We compare the parallax distances to those derived from radio pulse dispersion measures and find that they have systematically larger values, by 40 per cent on average. We also test the correlation between X-ray and spin-down luminosities, finding that most redbacks have a spin-down to X-ray luminosity conversion efficiency of ∼0.1 per cent, indicating a contribution from the intrabinary shock. On the other hand, most black widows have an efficiency of ∼0.01 per cent, similar to the majority of the pulsar population. Finally, we find that the bolometric optical luminosity significantly correlates with the orbital period, with a large scatter due to different irradiated stellar temperatures and binary properties. We interpret this correlation as the effect of the increasing size of the Roche Lobe radius with the orbital period. With this newly found correlation, an estimate of the optical magnitude can be obtained from the orbital period and a distance estimate. [ABSTRACT FROM AUTHOR]

The possible evolution of a bright low-mass X-ray binary system Sco X-1 is numerically investigated within the framework of a model assuming that the donor-star of the system (a satellite of a neutron star) fills its Roche lobe. The calculations consider a strong induced stellar wind (ISW) of the donor, which occurs due to irradiation by hard radiation of an accreting relativistic star. At the same time, using the example of Sco X-1, three hypotheses are investigated, within the framework of which a high rate of mass exchange can be obtained for semi-detached X-ray binaries. The first hypothesis is the presence of a strong ISW of the donor with standard magnetic braking. Calculations have shown that in this case it is possible to obtain a high rate of mass exchange, but at the same time the donor cannot fill the Roche lobe—it "goes under it." The second hypothesis is an increase of magnetic braking, that is, an increase of the loss of angular momentum from the system due to the magnetic stellar wind of the donor (MSW). Such an amplification may be associated with the intense ISW of the donor in the presence of a strong magnetic field. Numerical modeling shows that with an increase of MSW by times, a high rate of mass exchange is possible when the donor fills its Roche lobe. The third hypothesis suggests the possibility of canceling the direct exchange of angular momentum between the orbital moment of the system and the moment of accreted matter passing from a low-mass donor to a more massive accretor. With such cancellation, the main process, increasing the semi-axis of the orbit, disappears. Calculations show that in this case it is possible to obtain a sufficiently high rate of mass exchange. However, the most likely reason for the increase of the rate of mass exchange in low-mass X-ray binary systems is probably the increase of magnetic braking. [ABSTRACT FROM AUTHOR]

Black widows and redbacks are binary millisecond pulsars with close low-mass companions that are irradiated and gradually ablated by the pulsar's high-energy luminosity L irr. These binaries evolve primarily through magnetic braking, which extracts orbital angular momentum and pushes the companion to overflow its Roche lobe. Here, we use the stellar evolution code mesa to examine how the irradiation modifies the companion's structure. Strong L irr inhibits convection to the extent that otherwise fully convective stars become almost fully radiative. By computing the convective velocities and assuming a dynamo mechanism, we find that the thin convective envelopes of such strongly irradiated companions (⁠|$L_{\rm irr}\gtrsim 3\, {\rm L}_\odot$|⁠) generate much weaker magnetic fields than previously thought – halting binary evolution. With our improved magnetic braking model, we explain most observed black widow and redback companions as remnants of main-sequence stars. We also apply our model (with L irr) to evolved companions that overflow their Roche lobe close to the end of their main-sequence phase. The evolutionary tracks of such companions bifurcate, explaining the shortest period systems (which are potential gravitational wave sources) as well as the longest period ones (which are the progenitors of common pulsar–white dwarf binaries). The variety of black widow structures and evolutionary trajectories may be utilized to calibrate the dependence of magnetic braking on the size of the convective layer and on the existence of a radiative–convective boundary, with implications for single stars as well as other binaries, such as cataclysmic variables and AM Canum Venaticorum stars. [ABSTRACT FROM AUTHOR]

Helium white dwarfs (HeWDs) are thought to form from low-mass red giant stars experiencing binary interaction. Because the helium core mass of a red giant star is closely related to the stellar radius, there exists well-known relation between the orbital period (P orb) and the mass (M WD) of the HeWDs, which is almost independent of the type of the companion star. Traditional derivation of the M WD– P orb relation generally neglected the effect of wind mass-loss from the red giants, while observations show that wind mass-loss from red giants in binary systems is systematically higher than that from isolated stars. In this work, we calculate binary evolution with tidally enhanced stellar wind (TEW) and find that it causes significantly scatter of the traditional M WD– P orb relation. The TEW can prevent the red giants from overflowing their Roche lobes and slow down the growth of the helium core, leaving a lower mass HeWD for given orbital period. This scenario may account for some of the HeWD binaries that deviate from the traditional M WD– P orb relation. However, we point out that observations of more HeWD binaries in wide orbits are needed to test the TEW model and to constrain the enhanced wind factor. [ABSTRACT FROM AUTHOR]

We present 307 type Ia supernova (SN) light curves from the first 4 yr of the Transiting Exoplanet Survey Satellite mission. We use this sample to characterize the shapes of the early-time light curves, measure the rise times from first light to peak, and search for companion star interactions. Using simulations, we show that light curves must have noise <10% of the peak flux to avoid biases in the early-time light-curve shape, restricting our quantitative analysis to 74 light curves. We find that the mean power-law index t β 1 of the early-time light curves is β 1 = 1.93 ± 0.57, and the mean rise time to peak is 15.7 ± 3.5 days. The underlying population distribution for β 1 may instead consist of a Gaussian component with mean 2.29, width 0.34, and a long tail extending to values less than 1.0. We find that the data can rarely distinguish between models with and without companion interaction models. Nevertheless, we find three high-quality light curves that tentatively prefer the addition of a companion interaction model, but the statistical evidence for the companion interactions is not robust. We also find two SNe that disfavor the addition of a companion interaction model to a curved power-law model. Taking the 74 SNe together, we calculate 3 σ upper limits on the presence of companion signatures to control for orientation effects that can hide companions in individual light curves. Our results rule out common progenitor systems with companions having Roche lobe radii >31 R ⊙ (separations >5.7 × 1012 cm, 99.9% confidence level) and disfavor companions having Roche lobe radii >10 R ⊙ (separations >1.9 × 1012 cm, 95% confidence level). Lastly, we discuss the implications of our results for the intrinsic fraction of single degenerate progenitor systems. [ABSTRACT FROM AUTHOR]

We propose that the recently observed quasi-periodic eruptions (QPEs) in galactic nuclei are produced by unstable mass transfer due to Roche lobe overflow of a low-mass main-sequence star in a mildly eccentric (e ∼ 0.5) orbit. We argue that the QPE emission is powered by circularization shocks, but not directly by black hole (BH) accretion. Our model predicts the presence of a time-steady accretion disc that is bolometrically brighter than the time-averaged QPE luminosity, but primarily emits in the extreme-ultraviolet. This is consistent with the quiescent soft X-ray emission detected in between the eruptions in eROSITA QPE1, QPE2, and GSN 069. Such accretion discs have an unusual ν L ν ∝ ν12/7 optical spectrum. The lifetime of the bright QPE phase, 102–103 yr, is set by mass-loss triggered by ram-pressure interaction between the star and the accretion disc fed by the star itself. We show that the stellar orbits needed to explain QPEs can be efficiently created by the Hills breakup of tight stellar binaries provided that (i) the stellar binary orbit is tidally hardened before the breakup due to diffusive growth of the f-mode amplitude and (ii) the captured star's orbit decays by gravitational wave emission without significant orbital angular momentum diffusion (which is the case for low-mass BHs, M BH ≲ 106 M⊙). We conclude by discussing the implications of our model for hyper-velocity stars, extreme mass ratio inspirals, repeating partial TDEs, and related stellar phenomena in galactic nuclei. [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 origin of current angular momentum (AM) of the black hole (BH) in X-ray binary (XRB) is still unclear, which is related with the birth and/or the growth of the BH. Here, we collect the spin parameters a * measured in BH XRBs and find an apparent bimodal distribution centered at ∼ 0.17 and 0.83. We find a positive relation between the spin parameter and the orbital period/orbital separation through combining distinct XRB categories, including neutron star (NS) low-mass X-ray binaries (LMXBs), Roche lobe overflow (RLOF) BH XRBs, and wind-fed BH XRBs. It seems that the AM of the compact star and the binary orbit correlates by combining the different XRB systems. These positive relations imply that accretion process is a common mechanism for spinning up the compact star in these diverse XRB systems. We infer that the low and high spin BH XRBs may experience different evolution and accretion history, which corresponds to the bimodal distribution of the BH spin parameters. The low spin BHs (a * < 0.3) are similar to the NS LMXBs, the compact star of which is spun-up by the low-level accretion, and the high spin BHs (a * > 0.5) had experienced a short hypercritical accretion (⁠|$\gg \dot{M}_\mathrm{Edd}$|⁠) period, during which, the BH spin dramatically increased. [ABSTRACT FROM AUTHOR]

Low-mass X-ray binaries (LMXB) serve as natural laboratories, where the predictions of general relativity can be tested in the strong field regime. The primary object of such sources can be a neutron star (NS) or a black hole (BH), and this object captures material from the secondary object through the inner Lagrange point via a process called Roche lobe overflow. Because of the angular momentum of the infalling matter, an accretion disk is formed, in which viscous effects transport the angular momentum radially outward. In the high/soft state of these sources, the accretion disk can extend all the way to the innermost stable circular orbit (ISCO); therefore, when the primary object is a BH, its X-ray spectrum contains information about the region very close to the event horizon. This paper aims to review the theoretical and observational works related to the X-ray spectroscopy of such sources via the example of GX 339-4, which is one of the most well-known and well-studied LMXBs. [ABSTRACT FROM AUTHOR]

Calculation of the mass transfer (MT) rate |$\dot{M}_\text{d}$| of a Roche lobe overflowing star is a fundamental task in binary star evolution theory. Most of the existing MT prescriptions are based on a common set of assumptions that combine optically thick and optically thin regimes with different flow geometries. In this work, we develop a new model of MT based on the assumption that the Roche potential sets up a nozzle converging on the inner Lagrangian point and that the gas flows mostly along the axis connecting both stars. We derive a set of 1D hydrodynamic equations governing the gas flow with |$\dot{M}_\text{d}$| determined as the eigenvalue of the system. The inner boundary condition directly relates our model to the structure of the donor obtained from 1D stellar evolution codes. We obtain an algebraic solution for the polytropic equation-of-state (EOS). This gives |$\dot{M}_\text{d}$| within a factor of 0.9 to 1.0 of existing optically thick prescriptions and reduces to the existing optically thin prescription for isothermal gas. For a realistic EOS, we find that |$\dot{M}_\text{d}$| differs by up to a factor of 4 from existing models. We illustrate the effects of our new MT model on a |$30\, M_\odot$| low-metallicity star undergoing intensive thermal time-scale MT and find that it is more likely to become unstable to L2 overflow and common-envelope evolution than expected according to MT prescriptions. Our model provides a framework to include additional physics such as radiation or magnetic fields. [ABSTRACT FROM AUTHOR]

The results of photometric and spectral observations of T CrB obtained in a wide range of wavelengths in 2011–2023 are presented. We use the near-IR light curves to determine a new ephemeris for the times of light minima when the red giant is located between the observer and the hot component. The flux ratio H /H varied from to in 2020–2023, which may be due to a change in the flux ratio between the X-ray and optical ranges. It is shown that the value of H /H anticorrelates with the rate of accretion onto the hot component of the system. Based on high-speed follow-up observations obtained on June 8, 2023, we detected a variability of the He II line with a characteristic time-scale of min, the amplitude of variability in the -band was . Simulations of the near-IR light curves accounting for the ellipsoidal effect allowed us to obtain the parameters of the binary system: the Roche lobe filling factor of the cool component , the mass ratio , the orbital inclination . A comparison of the light curve obtained in 2005–2023 with the 1946 outburst template made it possible to predict the date of the upcoming outburst—January 2024. [ABSTRACT FROM AUTHOR]

RZ Hor (TIC 31653503) is a long-period (P = 6.68 d) EA-type eclipsing binary that exhibits both chromospheric activity and oscillation. The physical properties of RZ Hor are determined with binary modelling for the first time. It is found that it has a semi-detached configuration with a low mass ratio of q = 0.1606(13), where the secondary component is filled with its Roche lobe. By analyzing all available eclipse times, it is shown that the orbital period of RZ Hor is decreasing at a rate of dP / dt = −5.48 × 10−6 d yr−1. In a typical Algol, a rapid mass transfer from the secondary to the primary should cause the orbital period to be increasing and then the secondary will be temporarily detached from the critical Roche lobe. The present configuration reveals that RZ Hor has undergone a rapid mass transfer and the period decrease can be explained by magnetic stellar wind. We estimate the rate of mass loss initially to be |$10^{-8}\, M_{\odot }\, \mathrm{yr}^{-1} < \vert \dot{M}\vert < 10^{-6}\, M_{\odot }$|  yr−1. The variations and the asymmetries of the light curve are interpreted by adding a migrating cool spot on the surface of the late-type secondary. After subtracting the eclipsing changes from the light curve data, we analyzed the pulsation in the light residuals. Twenty-five frequencies of signal-to-noise amplitude ratio (S / N) larger than 5.2, including four multiples of tidally split frequencies, were detected. A total of 17 independent frequencies containing 2 radial modes, and 10 non-radial p modes were identified. All the investigations suggest that RZ Hor is an evolved Algol-type binary with a δ Sct-type primary and an active secondary. [ABSTRACT FROM AUTHOR]

We present a summary of the results of the OJ 287 observational campaign, which was carried out during the 2021/2022 observational season. This season is special in the binary model because the major axis of the precessing binary happens to lie almost exactly in the plane of the accretion disc of the primary. This leads to pairs of almost identical impacts between the secondary black hole and the accretion disk in 2005 and 2022. In 2005, a special flare called "blue flash" was observed 35 days after the disk impact, which should have also been verifiable in 2022. We did observe a similar flash and were able to obtain more details of its properties. We describe this in the framework of expanding cloud models. In addition, we were able to identify the flare arising exactly at the time of the disc crossing from its photo-polarimetric and gamma-ray properties. This is an important identification, as it directly confirms the orbit model. Moreover, we saw a huge flare that lasted only one day. We may understand this as the lighting up of the jet of the secondary black hole when its Roche lobe is suddenly flooded by the gas from the primary disk. Therefore, this may be the first time we directly observed the secondary black hole in the OJ 287 binary system. [ABSTRACT FROM AUTHOR]

The detonation of an overlying helium layer on a 0.8–1.1 M ⊙ carbon–oxygen (CO) white dwarf (WD) can detonate the CO WD and create a thermonuclear supernova (SN). Many authors have recently shown that when the mass of the He layer is low (≲0.03 M ⊙), the ashes from its detonation minimally impact the spectra and light curve from the CO detonation, allowing the explosion to appear remarkably similar to Type Ia SNe. These new insights motivate our investigation of dynamical He shell burning and our search for a binary scenario that stably accumulates thermally unstable He shells in the 0.01–0.08 M ⊙ range, thick enough to detonate, but also often thin enough for minimal impact on the observables. We first show that our improved nonadiabatic evolution of convective He shell burning in this range of shell mass leads to conditions ripe for a He detonation. We also find that a stable mass transfer scenario with a high-entropy He WD donor of mass 0.15–0.25 M ⊙ yields the He shell masses needed to achieve the double detonations. This scenario also predicts that the surviving He donor leaves with a spatial velocity consistent with the unusual runaway object, D6-2. We find that hot He WD donors originate in common-envelope events when a 1.3–2.0 M ⊙ star fills its Roche lobe at the base of the red giant branch at orbital periods of 1–10 days with the CO WD. [ABSTRACT FROM AUTHOR]

The article offers information on the longest tails of gas observed escaping a planet by a team of astronomers using the Habitable-zone Planet Finder Spectrograph (HPF) on Hobby-Eberly Telescope (HET). It mentions that Jupiter HAT-P-32 b was observed using high-resolution spectroscopy which measured helium equivalent widths (EWs) for all HPF spectra of HAT-P-32 A+ b and that three-dimensional (3D) hydrodynamic simulations of the system provided physical insight into the geometry of the outflow.

It has been proposed that accretion-induced collapse (AIC) of massive white-dwarfs (WDs) is an indispensable path for the formation of neutron star (NS) binaries. Although there are still no direct evidence for the existence of AIC events, several kinds of NS systems are suggested to originate from the AIC processes. One of the representative evidence is the detection of the strong magnetic field and slow spin NSs with ultra-light companions (⁠|${\le}0.1\, \rm M_{\odot }$|⁠) in close orbits. However, previous studies cannot explain the formation of AIC events with such low-mass companions. In the present work, we evolve a series of ONe WD+He WD systems to the formation of AIC events (named as the He WD donor channel), and the NS binaries behave as ultra-compact X-ray binaries when the He WDs refill their Roche lobes. We found that the ONe WD+He WD systems a possible channel for the formation of the newly formed NS+ultra-light companion systems just after the AIC event. Although there are some other inconsistent properties, the detected companion mass and orbital period of 4U 1626–67 (one of the newly formed NS binaries with ultra-light companions) can be reproduced by the He WD donor channel. In addition, combined with previous asteroseismology results, we speculate that an UCXB source (XTE J1751−305) may originate from the He WD donor channel. [ABSTRACT FROM AUTHOR]

Many stars live in hierarchical triple systems, but the physics of such systems are still poorly understood. One understudied physical aspect of these systems is tertiary tides, wherein the tidal deformation of a tertiary in a hierarchical triple drains energy from the inner binary, causing the inner binary's orbital separation to decrease. This tidal process is difficult to observe directly, since such an observation requires a very compact hierarchical triple, the tertiary of which must be almost large enough to fill its Roche lobe at the epoch of observation. Concurrently, the recently discovered stellar system TIC242132789 is the fourth most compact observed hierarchical triple, and the most compact in which the tertiary is a giant. In this paper, we demonstrate that TIC242132789 provides a rare opportunity to place constraints on the model parameters for tertiary tides, and can even be a rare opportunity to directly observe tertiary-tides-induced orbital shrinkage of the inner binary. We calculate our expectations of how fast the inner orbit will shrink, and demonstrate that our estimates of this rate of shrinkage should be observable using current techniques. We conclude with a call for relevant observations of this system to commence. [ABSTRACT FROM AUTHOR]

Various interactions affect the population of close-in planets. Among them, the tidal and magnetic interactions drive orbital decay and star-planet angular momentum exchange, leading to stellar spin-up. As a result of the above processes, a planet may initiate the mass transfer to the host star once it encounters the Roche limit. Another mechanism providing substantial mass-loss is associated with the atmospheric escape caused by photoevaporation followed by orbital expansion, which is thought to be important for hot Neptunes and super-Earths. Thus, the fraction of the initial number of hot Jupiters may transform into lower-mass planets through the Roche lobe overflow (RLO) phase and continue secular evolution under the effect of photoevaporation. In this paper, we compile the latest prescriptions for tidal and magnetic migration and mass-loss rates to explore the dynamics of hot Jupiter systems. We study how the implemented interactions shape the orbital architecture of Jovian planets and whether their impact is enough to reproduce the observational sample. Our models suggest that the tidal interaction is able to generate the upper boundary of the hot Jupiter population in the mass–separation diagram. To recreate the sub-Jovian desert, we need to make additional assumptions regarding the RLO phase or the influence of the protoplanetary disc's inner edge on the initial planetary location. According to our estimates, 12–15 per cent of hot Jupiters around solar-mass stars have been engulfed or become lower-mass planets. 0.20–0.25 per cent of the present-day giant planet population undergoes decay intense enough to be detected with modern facilities. [ABSTRACT FROM AUTHOR]

We discuss the formation and evolution of systems composed of a low-mass (M ⋆ ≲ 4 M ⊙) main-sequence star orbiting a 105–107 M ⊙ supermassive black hole with an orbital period of order ∼hours and a mild eccentricity (e ≈ 0.1–0.2), episodically shedding mass at each pericenter passage. We argue that the resulting mass transfer is likely unstable, with Roche lobe overflow initially driven by gravitational-wave emission, but then being accelerated by the star's expansion in response to its mass loss, undergoing a runaway process. We show that such systems are naturally produced by two-body gravitational encounters within the inner parsec of a galaxy, followed by gravitational-wave circularization and inspiral from initially highly eccentric orbits. We argue that such systems can produce recurring flares similar to the recently identified class of X-ray transients known as quasiperiodic eruptions, observed at the centers of a few distant galaxies. [ABSTRACT FROM AUTHOR]

We model helium-rich stars with solar metallicity (X  = 0.7, Z  = 0.02) progenitors that evolve to form AM Canum Venaticorum systems through a helium-star formation channel, with the aim to explain the observed properties of Gaia14aae and ZTFJ1637+49. We show that semidegenerate, H-exhausted (X ≤ 10−5), He-rich (Y ≈ 0.98) donors can be formed after a common envelope evolution (CEE) phase if either additional sources of energy are used to eject the common envelope, or a different formalism of CEE is implemented. We follow the evolution of such binary systems after the CEE phase using the Cambridge stellar evolution code when they consist of a He-star and a white dwarf accretor, and report that the mass, radius, and mass-transfer rate of the donor, the orbital period of the system, and the lack of hydrogen in the spectrum of Gaia14aae and ZTFJ1637+49 match well with our modelled trajectories wherein, after the CEE phase Roche lobe overflow is governed not only by the angular momentum loss (AML) owing to gravitational wave radiation (AMLGR) but also an additional AML owing to α–Ω dynamos in the donor. This additional AML is modelled with our double-dynamo (DD) model of magnetic braking in the donor star. We explain that this additional AML is just a consequence of extending the DD model from canonical cataclysmic variable donors to evolved donors. We show that none of our modelled trajectories match with Gaia14aae or ZTFJ1637+49 if the systems are modelled only with AMLGR. [ABSTRACT FROM AUTHOR]

Barium stars have been studied extensively over the past few decades, yet our current understanding of how these intriguing objects formed leaves much to be desired. Many trends observed in systems containing barium stars cannot be satisfactorily explained by classical binary evolution models, naturally raising the question of whether triples and other higher order multiples can give rise to such exotic objects. In this paper, we study the possibility that a Roche Lobe overflow from a tertiary in a hierarchical triple system can potentially lead to surface barium enrichment within the inner binary, while at the same time causing the inner binary to merge, thereby producing a barium star. This possibility has the potential to form a large proportion of Barium stars, as Roche Lobe overflow from a tertiary is typically much more stable for close orbits than that from a binary companion. Various formation channels and mechanisms by which this can be achieved are considered, and constraints on relative formation rates are placed on each scenario. Three recently discovered triple systems containing Ba stars further support our proposed formation mechanism. We conclude that a significant portion of barium stars may be formed from hierarchical triple systems, and that further studies are required in this area before a complete understanding of Barium star populations can be achieved. [ABSTRACT FROM AUTHOR]

Common envelope (CE) systems are the result of Roche lobe overflow in interacting binaries. The subsequent evolution of the CE, its ejection, and the formation of dust in its ejecta while the primary is on the red giant branch (RGB) gives rise to a recently identified evolutionary classâ€"dusty post-RGB stars. Their spectral energy distributions (SEDs) suggest that their mass-ejecta are similar to dusty post-asymptotic giant branch (post-AGB) stars. We have modeled the SEDs of a select sample of post-RGB and post-AGB stars in the Large Magellanic Cloud, quantified the total dust mass (and gas mass assuming gas-to-dust ratio) in the disks and shells and set constraints on the dust grain compositions and sizes. We find that the shell masses in the post-RGBs are generally less than those in post-AGBs, with the caveat that substantial amount of mass in both types of objects may lie in cold, extended shells. Our models suggest that circumstellar disks, when present, are geometrically thick structures with a substantial opening angle, consistent with numerical simulations of CE evolution (CEE). Comparison of our model dust masses with the predictions of dust production during CEE on the RGB suggest that CEE occurred near or at the tip of the RGB for our post-RGB sources. A surprising result is that some post-RGB stars harbor carbon-rich dust, believed to form when C/O > 1, e.g., following triple-alpha nucleosynthesis and third dredge-up events in AGB stars. This anomaly strengthens the hypothesis that dusty post-RGBs are born in binary systems. [ABSTRACT FROM AUTHOR]

AR Scorpii (AR Sco) is the only radio-pulsing white dwarf known to date. It shows a broad-band spectrum extending from radio to X-rays whose luminosity cannot be explained by thermal emission from the system components alone, and is instead explained through synchrotron emission powered by the spin-down of the white dwarf. We analysed NTT/ULTRACAM, TNT/ULTRASPEC, and GTC/HiPERCAM high-speed photometric data for AR Sco spanning almost seven years and obtained a precise estimate of the spin frequency derivative, now confirmed with 50-σ significance. Using archival photometry, we show that the spin-down rate of |$P/\dot{P} = 5.6 \times 10^6$|  yr has remained constant since 2005. As well as employing the method of pulse-arrival time fitting used for previous estimates, we also found a consistent value via traditional Fourier analysis for the first time. In addition, we obtained optical time-resolved spectra with WHT/ISIS and VLT/X-shooter. We performed modulated Doppler tomography for the first time for the system finding evidence of emission modulated on the orbital period. We have also estimated the projected rotational velocity of the M-dwarf as a function of orbital period and found that it must be close to Roche lobe filling. Our findings provide further constraints for modelling this unique system. [ABSTRACT FROM AUTHOR]

Within the framework of the induced stellar wind (ISW) model, the possible evolution of the X-ray binary system Sco X-1 after the formation of a neutron star in it is simulated and theoretically reproduced. We showed that, within the allowable limits of the ISW model parameter interval, it is possible to reproduce the system characteristics obtained earlier in the model of incomplete filling of the Roche lobe with a donor—an optical star (with a filling factor of 0.38) by modeling the optical orbital light curves of Sco X-1. The high rate of mass loss by the donor is due to its irradiation with hard radiation arising from accretion onto a neutron star. In the tracks that seem to be the most suitable for the evolution of Sco X-1, we obtained the same filling factor of the Roche lobe by the donor (0.38). According to the results of our calculations, the most probable value of the initial mass of the donor at the time of formation of a neutron star in the system does not greatly exceed its current mass and can be close to (0.5–0.7) . The ratio of the donor stellar wind velocity to the parabolic velocity on its surface αISW in our calculations turns out to be close to 0.5–0.6. The main meaning of this parameter in our model is to determine the fraction of the donor matter captured by the accretor. With such , this fraction is quite large, which is necessary for the appearance of an intense ISW. However, in a real system, there may be processes that increase this fraction even at high wind speeds. Thus, its real rate can be higher than the rate corresponding to values of obtained by us. [ABSTRACT FROM AUTHOR]

We present simultaneous, multicolour optical light curves of the companion star to the black-widow pulsar PSR J2051−0827, obtained approximately 10 yr apart using ULTRACAM and HiPERCAM, respectively. The ULTRACAM light curves confirm the previously reported asymmetry in which the leading hemisphere of the companion star appears to be brighter than the trailing hemisphere. The HiPERCAM light curves, however, do not show this asymmetry, demonstrating that whatever mechanism is responsible for it varies on time-scales of a decade or less. We fit the symmetrical HiPERCAM light curves with a direct-heating model to derive the system parameters, finding an orbital inclination of |$55.9^{+4.8}_{-4.1}$| degrees, in good agreement with radio-eclipse constraints. We find that approximately half of the pulsar's spin-down energy is converted to optical luminosity, resulting in temperatures ranging from approximately |$5150^{+190}_{-190}$|  K on the day side to |$2750^{+130}_{-150}$|  K on the night side of the companion star. The companion star is close to filling its Roche lobe (⁠|$f_{\rm RL} =0.88^{+0.02}_{-0.02}$|⁠) and has a mass of |$0.039^{+0.010}_{-0.011}$|  M⊙, giving a mean density of |$20.24^{+0.59}_{-0.44}$|  g cm−3 and an apsidal motion constant in the range 0.0036 < k 2 < 0.0047. The companion mass and mean density values are consistent with those of brown dwarfs, but the apsidal motion constant implies a significantly more centrally condensed internal structure than is typical for such objects. [ABSTRACT FROM AUTHOR]

Most back hole and neutron star progenitors are found in triples or higher multiplicity systems. Here, we present a new triple stellar evolution code, |${\tt TSE}$|⁠ , which simultaneously takes into account the physics of the stars and their gravitational interaction. |${\tt TSE}$| is used to simulate the evolution of massive stellar triples in the galactic field from the zero-age main sequence until they form compact objects. To this end, we implement initial conditions that incorporate the observed high correlation between the orbital parameters of early-type stars. We show that the interaction with a tertiary companion can significantly impact the evolution of the inner binary. High eccentricities can be induced by the third-body dynamical effects, leading to a Roche lobe overflow or even to a stellar merger from initial binary separations 103– |$10^5\, \rm R_\odot$|⁠. In |$\sim 5\, {{\ \rm per\ cent}}$| of the systems, the tertiary companion itself fills its Roche lobe, while |$\sim 10\, {{\ \rm per\ cent}}$| of all systems become dynamically unstable. We find that between |$0.3{{\ \rm per\ cent}}$| and |$5{{\ \rm per\ cent}}$| of systems form a stable triple with an inner compact object binary, where the exact fraction depends on metallicity and the natal kick prescription. Most of these triples are binary black holes with black hole companions. We find no binary neutron star in any surviving triple, unless zero natal kicks are assumed. About half of all black hole binaries formed in our models are in triples, where in the majority, the tertiary black hole can perturb their long-term evolution. Our results show that triple interactions are key to a full understanding of massive star evolution and compact object binary formation. [ABSTRACT FROM AUTHOR]

Binaries consisting of a hot subdwarf star and an accreting white dwarf (WD) are sources of gravitational wave radiation at low frequencies and possible progenitors of Type Ia supernovae if the WD mass is large enough. Here, we report the discovery of the third binary known of this kind: It consists of a hot subdwarf O (sdO) star and a WD with an orbital period of 3.495 h and an orbital shrinkage of 0.1 s in 6 yr. The sdO star overfills its Roche lobe and likely transfers mass to the WD via an accretion disc. From spectroscopy, we obtain an effective temperature of |$T_{\mathrm{eff}}=54\, 240\pm 1840$| K and a surface gravity of log  g  = 4.841 ± 0.108 for the sdO star. From the light curve analysis, we obtain an sdO mass of M sdO = 0.55 M⊙ and a mass ratio of q  = M WD/ M sdO = 0.738 ± 0.001. Also, we estimate that the disc has a radius of |$\sim\!0.41\ \mathrm{R}_\odot$| and a thickness of |$\sim\!0.18\ \mathrm{R}_\odot$|⁠. The origin of this binary is probably a common envelope ejection channel, where the progenitor of the sdO star is either a red giant branch star or, more likely, an early asymptotic giant branch star; the sdO star will subsequently evolve into a WD and merge with its WD companion, likely resulting in an R Coronae Borealis (R CrB) star. The outstanding feature in the spectrum of this object is strong Ca H&K lines, which are blueshifted by ∼200 km s−1 and likely originate from the recently ejected common envelope, and we estimated that the remnant common envelope (CE) material in the binary system has a density |$\sim\!6\times 10^{-10}\ {\rm g\, cm}^{-3}$|⁠. [ABSTRACT FROM AUTHOR]

Ultraluminous X-ray bursts (ULXBs) are ultraluminous X-ray flares with a fast rise (∼1 minute) and a slow decay (∼1 hour), which are commonly observed in extragalactic globular clusters. Most ULXBs are observational one-off bursts, whereas five flares from the same source in NGC 5128 were discovered by Irwin et al. In this article, we propose a neutron star (NS)â€"white dwarf (WD) binary model with super-Eddington accretion rates to explain the repeating behavior of the ULXB source in NGC 5128. With an eccentric orbit, the mass transfer occurs at the periastron where the WD fills its Roche lobe. The ultraluminous X-ray flares can be produced by the accretion column around the NS magnetic poles. On the other hand, some repeating fast radio bursts (FRBs) were also found in extragalactic globular clusters. Repeating ULXBs and repeating FRBs are the most violent bursts in the X-ray and radio bands, respectively. We propose a possible association between the repeating ULXBs and the repeating FRBs. Such an association is worth further investigation by follow-up observations on nearby extragalactic globular clusters. [ABSTRACT FROM AUTHOR]

Roche lobe overflow from a donor star onto a black hole or neutron star binary companion can evolve to a phase of unstable runaway mass transfer, lasting as short as hundreds of orbits (≲102 yr for a giant donor) and eventually culminating in a common-envelope event. The highly super-Eddington accretion rates achieved during this brief phase ( M ̇ ≳ 10 5 M ̇ Edd) are accompanied by intense mass loss in disk winds, analogous to but even more extreme than ultraluminous X-ray (ULX) sources in the nearby universe. Also in analogy with the observed ULX, this expanding outflow will inflate an energetic “bubble” of plasma into the circumbinary medium. Embedded within this bubble is a nebula of relativistic electrons heated at the termination shock of the faster v ≳ 0.1 c wind/jet from the inner accretion flow. We present a time-dependent, one-zone model for the synchrotron radio emission and other observable properties of such ULX “hypernebulae.” If ULX jets are sources of repeating fast radio bursts (FRB), as recently proposed, such hypernebulae could generate persistent radio emission and contribute large and time-variable rotation measure to the bursts, consistent with those seen from FRB 20121102 and FRB 20190520B. ULX hypernebulae can be discovered independently of an FRB association in radio surveys, such as VLASS, as off-nuclear point sources whose fluxes can evolve significantly on timescales as short as years, possibly presaging energetic transients from common-envelope mergers. [ABSTRACT FROM AUTHOR]

Black widows (BWs) are a type of eclipsing millisecond pulsars (MSPs) with companion masses |$M_2\lesssim 0.05\, \rm M_\odot$|⁠ , which can be used to study the accretion history and the radiation of pulsars, as well as the origin of isolated MSPs. Recent observations indicate that there are two subtypes of BWs. One is the BWs with |$M_2 \sim 0.01\!-\!0.05\, \rm M_\odot$|⁠ , whereas another with |$M_2 \lesssim 0.01\, \rm M_\odot$|⁠. However, the origin of the latter is still highly uncertain. In this paper, we investigated the formation of BWs with |$M_2 \lesssim 0.01\, \rm M_\odot$| through ultracompact X-ray binaries (UCXBs) with He star companions, in which a neutron star (NS) accretes material from a He star through Roche lobe overflow. By considering different He star masses and evaporation efficiencies with the stellar evolution code Modules for Experiments in Stellar Astrophysics (mesa), we evolved a series of NS+He star systems that can undergo UCXB stage. This channel can explain the formation of the BWs with |$M_2 \lesssim 0.01\, \rm M_\odot$| within the Hubble time, especially three widely studied BWs, i.e. PSRs J1719−1438, J2322−2650, and J1311−3430. We found that X-ray irradiation feedback does not affect the evolutionary tracks of evaporation process. The simulations indicate that the UCXBs with He star companions are the potential progenitors of isolated MSPs, and that the origin of BWs with |$M_2 \lesssim 0.01\, \rm M_\odot$| is different with another subtype of BWs. In addition, this work suggests that the BWs with |$M_2 \lesssim 0.01\, \rm M_\odot$| may not be produced by redback systems. [ABSTRACT FROM AUTHOR]

We revisit various sets of published results from X-ray and optical studies of the Galactic black hole (BH) candidate MAXI J0637-430, which went into outburst in 2019. Combining the previously reported values of peak outburst luminosity, best-fitting radii of inner and outer accretion disc, viewing angle, exponential decay time-scale, and peak-to-peak separation of the He II λ4686 disc emission line, we improve the constraints on the system parameters. We estimate a heliocentric distance d ≈ (8.7 ± 2.3) kpc, a projected Galactocentric distance R ≈ (13.2 ± 1.8) kpc and a height | z | ≈ (3.1 ± 0.8) kpc from the Galactic plane. It is the currently known Milky Way BH candidate located farthest from the Galactic Centre. We infer a BH mass M 1 ≈ (5.1 ± 1.6)M⊙, a spin parameter a * ≲ 0.25, a donor star mass M 2 ≈ (0.25 ± 0.07)M⊙, a peak Eddington ratio λ ≈ 0.17 ± 0.11 and a binary period |$P_{\rm orb} \approx 2.2^{+0.8}_{-0.6}$|  hr. This is the shortest period measured or estimated so far for any Galactic BH X-ray binary. If the donor star is a main-sequence dwarf, such a period corresponds to the evolutionary stage where orbital shrinking is driven by gravitational radiation and the star has regained contact with its Roche lobe (low end of the period gap). The three Galactic BHs with the shortest period (≲3 hr) are also those with the highest vertical distance from the Galactic plane (≳2 kpc). This is probably because binaries with higher binding energies can survive faster natal kicks. [ABSTRACT FROM AUTHOR]

The third data release of the Gaia mission includes orbital solutions for >105 single-lined spectroscopic binaries, representing more than an order of magnitude increase in sample size over all previous studies. This data set is a treasure trove for searches for quiescent black hole + normal star binaries. We investigate one population of black hole candidate binaries highlighted in the data release: sources near the main sequence in the colour–magnitude diagram (CMD) with dynamically inferred companion masses M 2 larger than the CMD-inferred mass of the luminous star. We model light curves, spectral energy distributions, and archival spectra of the 14 such objects in DR3 with high-significance orbital solutions and inferred |$M_2 \gt 3\, {\rm M}_{\odot }$|⁠. We find that 100 per cent of these sources are mass-transfer binaries containing a highly stripped lower giant donor (0.2 ≲ M /M⊙ ≲ 0.4) and much more massive (2 ≲ M /M⊙ ≲ 2.5) main-sequence accretor. The Gaia orbital solutions are for the donors, which contribute about half the light in the Gaia RVS bandpass but only |$\lesssim 20{{\ \rm per\ cent}}$| in the g band. The accretors' broad spectral features likely prevented the sources from being classified as double-lined. The donors are all close to Roche lobe filling (⁠|$R/R_{\rm Roche\, lobe}\gt 0.8$|⁠), but modelling suggests that a majority are detached (⁠|$R/R_{\rm Roche\, lobe}\lt 1$|⁠). Binary evolution models predict that these systems will soon become detached helium white dwarf + main-sequence 'EL CVn' binaries. Our investigation highlights both the power of Gaia data for selecting interesting subpopulations of binaries and the ways in which binary evolution can bamboozle standard CMD-based stellar-mass estimates. [ABSTRACT FROM AUTHOR]

We report on the evolution of X-ray spectral and timing properties of the X-ray binary MAXI J1727 − 203 based on NICER/XTI and MAXI/GSC observations. Over the course of the outburst, a transition from the intermediate state to the high/soft state, and then back to the low/hard state was observed. During the high/soft state, the innermost radius estimated from the multi-colour disc model remained constant at |$\sim 145.0\ (\frac{D}{10\ \mathrm{kpc}}) \ {(\frac{\cos i}{\cos 0^{\circ }})}^{-1/2}$| km, where D is the source distance and i is the inclination. Assuming that the binary system contain a Schwarzschild black hole and has an inclination angle of 0°–84°, and considering the typical Eddington ratio at the transition back to the low/hard state, the black hole mass was estimated to be M ≥ 11.5 M⊙ for a distance of D ≥ 5.9 kpc. We also attempted to constrain the black hole mass and distance with a different method by combining the results from optical and near-infrared photometric observations. We modelled the near-infrared to X-ray spectral energy distributions obtained in the outburst period with an irradiated disk model, and estimated the lower limit of the black hole mass for a given distance, assuming both accretion disk and companion star fill their Roche lobe. The lower limit was, however, found to be much higher than the constraint obtained from the X-ray data. We discuss several possible causes of this inconsistency. It is difficult to fully resolve the conflict by a single cause and hence a combination of causes is required. [ABSTRACT FROM AUTHOR]