Context. Long-period Wolf-Rayet (WR) star binaries produced by mass transfer are predicted to be abundant, but are observationally rare. This yields constraints on the evolution of initially wide O star binaries, including those potentially leading to the formation of gravitational-wave sources through the Common Envelope Channel. Aims. We investigate this issue in the light of a new type of orbital evolution for initially wide O star binaries, which is driven by mass ejection at periastron passage during the Luminous Blue Variable (LBV) phase. Methods. The assumption that the mass ejection occurs instantly at periastron passage allows us to analytically describe the orbital evolution. This approach is motivated by our understanding of an Eddington-limit driven LBV phase. We perform population synthesis calculations for the WR stars in the Small Magellanic Cloud (SMC), and compare them to the observed SMC WR star population. Results. Different from mass transfer, our mass ejection scenario leads to increased orbital periods and eccentricities. The Galactic system WR 140 (orbital period 2895 d, eccentricity 0.9) could be a typical result of this evolution scenario. Our models predict measurable binary space velocities, and allow for the disruption of the binary. Our SMC population synthesis model predicts statistically 5.3 close, 3.7 long-period, and further 2 runaway single WR stars. With largely increased orbital periods and eccentricities, such WR+O star binaries may not be ruled out by past radial-velocity searches. Applying our scenario to the Gaia BH1 and BH2 systems, we find that it provides viable progenitor evolution models. Conclusions. The mass-ejection-driven orbital evolution could explain why so few wide WR binaries are observed, and why some of the apparently single WR stars have high space velocities. We discuss implications for gravitational-wave sources.

Recent studies have revealed discrepancies between observations and the predictions of the standard magnetic braking (MB). Although alternative models have been broadly discussed in neutron star binaries, they have not been systematically tested in cataclysmic variables (CVs). In this work, we investigate the performance of four MB models in CVs: the standard MB, the convection and rotation boosted (CARB) model, the tau-boosted model, and the saturated, boosted, and disrupted (SBD) model. We find that both the CARB and tau-boosted models appear too strong, so it fails to reproduce the location of the period gap in CVs, indicating that they are not appropriate for CVs. Furthermore, we present a comparison between the standard MB and the SBD models. Compared with the standard model, although the SBD model can better reproduce some observational features, it also exacerbates certain discrepancies between theory and observations. We also find that different prescriptions for the convective turnover timescale have a significant impact on the results in the nonstandard MBs. Finally, we discuss the impact of the SBD model on the formation and evolution of AM CVn.

Binary evolution plays a central role in producing rapidly rotating stars. Previous studies have shown that mass gainers in binaries can reach critical rotation after accreting only modest amounts of material, particularly during thermal-timescale Case B mass transfer, in which tidal spin-down is ineffective due to wide orbits. However, such rapid accretion often drives the mass gainer out of thermal equilibrium, and its subsequent spin evolution during thermal relaxation has not been analyzed in depth. In this study, we construct a suite of accreting detailed single-star models with different accretion prescriptions, which inflate and spin up to critical rotation during the accretion. After the accretion has ended, the models relax thermally and deflate. We find that the ratio of surface to critical angular velocity decreases to subcritical values during thermal contraction, with the magnitude of this decrease correlating with the degree of thermal disequilibrium at the end of accretion. This reduction in fractional critical rotation is even stronger when internal angular momentum transport is inefficient. Detailed binary models show the same trend, indicating that the results from our toy single-star models also apply to real binary evolution. Our results highlight that binary mass transfer does not always produce critically rotating stars, but instead may yield a wide range of spin rates depending on the mass transfer and accretion history. Our findings offer new insights into the rotational properties of mass gainers in binaries, stellar merger products, and newly formed massive stars following accretion.

Context. Long-period Wolf-Rayet (WR) star binaries produced by mass transfer are predicted to be abundant, but they are observationally rare. This yields constraints on the evolution of initially wide O star binaries, including those potentially leading to the formation of gravitational-wave sources through the common envelope channel. Aims. We investigated this issue in the light of a new type of orbital evolution for initially wide O star binaries, which is driven by mass ejection at periastron passage during the luminous blue variable (LBV) phase. Methods. The assumption that the mass ejection occurs instantly at periastron passage allowed us to analytically describe the orbital evolution. This approach is motivated by our understanding of an Eddington limit-driven LBV phase. We performed population synthesis calculations for the WR stars in the Small Magellanic Cloud (SMC) and compared them to the observed SMC WR star population. Results. Different from mass transfer, our mass ejection scenario leads to increased orbital periods and eccentricities. The Galactic system WR 140 (orbital period 2895 d, eccentricity 0.9) could be a typical result of this evolution scenario. Our models predict measurable binary space velocities and allow for the disruption of the binary. Our SMC population synthesis model statistically predicts 5.3 close, 3.7 long-period, and 2 further runaway single WR stars. With largely increased orbital periods and eccentricities, such WR+O star binaries cannot be ruled out based on past radial-velocity searches. When applying our scenario to the Gaia BH1 and BH2 systems, we found that it provides viable progenitor evolution models. Conclusions. The mass-ejection-driven orbital evolution could explain why so few wide WR binaries are observed and why some of the apparently single WR stars have high space velocities. We discuss the implications for gravitational-wave sources as well.

As cataclysmic variables (CVs) that have evolved past their minimum orbital period, period bouncers have been proposed to be a substantial fraction of the CV population, yet the observed number is significantly lower, posing the “missing bouncer” problem. In this work, we present a multiband photometric selection method to search for new period bouncer candidates. We identify a specific locus for confirmed bouncers in the optical-UV-IR space. Using this locus, we selected 430 candidates within 500 pc. Crossmatching with eROSITA and XMM-Newton catalogs reveals 10 candidates (seven of which are new) with X-ray emission, indicative of accretion. X-ray spectral analysis of these candidates confirmed plasma temperatures consistent with confirmed bouncers. Based on these findings, we estimate a local space density of high-likelihood period bouncer candidates of approximately 4.1 × 10 ^−7 pc ^−3 . The nature of these candidates requires confirmation through follow-up observations.

We report the discovery of 19 new pulsars identified from archival observations of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) within Galactic latitudes ∣ b ∣ < 5° and declinations decl. < −5°. The dataset was recorded using FAST’s L -band 19 beam receiver and covered ∼3.6 deg ^2 with a cumulative integration time of ∼500 hr and a total raw data volume of ∼700 TB. Our search employed fast Fourier transform (FFT)–based and fast folding algorithm (FFA)–based periodic searches and the single-pulse search. These new pulsars have spin periods ranging from 0.03 to 5.54 s. Two have periods under 0.1 s, suggesting they are likely young pulsars or mildly recycled pulsars. Four pulsars exhibit dispersion measures (DMs) exceeding 1000 pc cm ^−3 , with PSR J1839–0558t having the highest value in our sample at ∼1271 pc cm ^−3 , providing valuable samples for pulsar studies in the high-DM regime. Two rotating radio transients, PSRs J1836–0552t and J1847–0624t, were detected by FFA and single-pulse searches but failed with the FFT-based searches. In addition, three faint pulsars that were also missed by FFT-based searches were successfully detected using FFA. These discoveries demonstrate the critical role of FFA in uncovering faint, long-period, and sporadic pulsars and highlight the significant potential of FAST archival data, especially when combined with longer integration times and complementary search techniques, to reveal rare and weak pulsar populations.

Context. The saturated, boosted, and disrupted (SBD) magnetic braking (MB) model is an empirical prescription that has recently gained support from observations of diverse close binary systems. Different boosting (K) and disruption (η) parameters appear necessary for different systems, but their physical origins remain uncertain. Aims. We aim to identify the physical mechanisms that boost MB and cause its disruption at the fully convective boundary in cataclysmic variables (CVs). Methods. We modelled CV evolution using the MESA code and compared the results with observed CV properties. We computed the convective turnover time (τc) directly from the donor’s structure rather than adopting empirical relations. We also included irradiation from the accreting white dwarf, which heats the donor’s outer layers and can drive additional winds that enhance MB. Results. The structure-based τc calculation reveals a pronounced spike as the donor approaches full convection, which drives the disruption parameter (η) and initiates the period gap in CVs. The outcome of irradiation is sensitive to the accretion, irradiation, and wind efficiencies, as well as to the base wind mass-loss rate of M-dwarf donors, all of which are poorly constrained from observations. Despite these uncertainties, plausible parameter choices allow irradiation-driven winds to provide the required boost (K) during accreting phases. We refer to the combined prescription as the iτSBD MB model and find that it yields evolutionary tracks broadly consistent with the main CV properties. Conclusions. Our iτSBD MB framework offers a physically motivated interpretation of the empirical boost and disruption factors in SBD MB for CV evolution. We suggest that the convective turnover time spike at the fully convective boundary may be the universal driver of MB disruption for fast-rotating stars in the saturated regime, while irradiation-driven winds may be the dominant mechanism boosting MB in accreting binaries and other strongly irradiated close systems.

X-ray pulsars (XRPs) consist of a magnetized neutron star (NS) and an optical donor star. The NS accretes matter from the donor star, producing pulsed X-ray emission. In most cases, the donor stars are Be stars, and accretion is episodic, that is, the NSs are generally X-ray dim but occasionally experience outbursts. Here, we carry out a statistical study with the X-ray monitoring data and obtain strong correlations between the spin periods of the NSs and the outburst parameters for the first time. We show that XRPs containing faster rotating NSs tend to display more violent eruptions. In addition, pulsating ultraluminous X-ray sources in nearby galaxies follow a similar relationship. We demonstrate that most of these systems are close to the spin equilibrium, and that brighter pulsars have acquired more angular momentum by accreting matter from their companion stars, resulting in faster rotating NSs.

Low-mass galaxies are the building blocks of massive galaxies in the framework of hierarchical structure formation. To enable detailed studies of galactic ecosystems in dwarf galaxies by spatially resolving different galactic components, we have carried out the Dwarf Galaxy Integral-field Survey (DGIS). This survey aims to acquire observations with spatial resolutions as high as 10–100 pc while maintaining reasonably high signal-to-noise ratios with the Very Large Telescope/MUSE and ANU-2.3 m/WiFeS. The whole sample will be composed of 63 dwarf galaxies with M _* < 10 ^9 M _⊙ , selected from the Spitzer Local Volume Legacy survey. The overall scientific goals include studying baryonic cycles in dwarf galaxies, searching for off-nuclear (intermediate)-massive black holes, and quantifying the inner density profiles of dark matter. In this work, we describe the sample selection, data reduction, and high-level data products. By integrating the spectra over the field of view for each galaxy, we obtained the integrated gas-phase metallicity and discussed its dependence on stellar mass and star formation rate (SFR). We find that the overall relation between metallicity and stellar mass of our DGIS nearly follows the extrapolation from the higher mass end. Its dispersion does not decrease by invoking the dependence on SFR.

Huntsman systems are a recently identified and rare subclass of millisecond pulsar (MSP) binaries, characterized by a detached neutron star and an evolved giant companion in relatively wide orbits. Their formation has been proposed to involve red-bump-induced detachment, whereas the influence of MSP-driven evaporation during this evolutionary stage has not yet been quantitatively assessed. We quantify the influence of MSP-driven evaporation on the formation and evolution of Huntsman systems and assess its effects on their observable properties. We performed detailed binary evolution calculations including MSP-driven evaporation over a wide range of initial binary parameters and combined them with binary population synthesis to predict the observable population of Huntsman systems. We find that Huntsman systems originate primarily from binaries undergoing Case B mass transfer and red-bump-induced detachment, with initial donor masses of 1.0-2.5 M_⊙ and orbital periods above the bifurcation period. Evaporation has a secondary effect, slightly modifying the orbital evolution and the duration of the detached phase, but does not significantly alter the formation parameter space or the expected population, which contains about 10 Huntsman systems. We further show that evaporation can produce systematic shifts in the white dwarf mass-orbital period relation at the low-mass end, leading to systematically wider final orbits for a given white dwarf mass.

Helium stars stripped of their hydrogen envelopes represent pivotal phases in binary evolution, yet their origins, particularly within the intermediate-mass range of 2-8 M circle dot, still remain poorly understood. This population bridges the gap between low-mass hot subdwarfs and massive Wolf-Rayet stars, but has remained largely unobserved. In this study, we employ binary population synthesis to systematically investigate the formation and properties of intermediate-mass helium stars (IMHeS) across various galactic metallicities. Our results indicate that metallicity and common-envelope ejection efficiency are the dominant factors shaping the IMHeS population. We estimate that several thousand IMHeS exist in the Milky Way, with several hundred more in the Magellanic Clouds. The vast majority of IMHeS reside in binaries, with fewer than 10% appearing as single stars. Among IMHeS binaries, greater than or similar to 50% are expected to have main-sequence companions, and the remainder host compact companions (including helium stars, white dwarfs, neutron stars, or black holes). The former systems form mainly through stable mass transfer, whereas the latter arise predominantly from common envelope evolution. Our work provides quantitative predictions for the populations of these elusive stars formed through binary interactions and offers guidance for future observational searches.

Pulse profile modelling is a relativistic ray-tracing technique used to infer neutron star mass, radius, and surface hotspot properties from X-ray pulsations. Pulse profile modelling has been widely applied to rotation-powered millisecond pulsars, where the local environment is relatively empty. Application to accreting millisecond pulsars is complicated by the geometry of the local accretion flow, including disc occultation of surface emission. In this work, we extend an established pulse profile modelling code, X-PSI, to incorporate accretion disc occultation in accreting millisecond pulsar pulse profile modelling. We quantify how disc occultation depends on system geometry and evaluate its impact on parameter inference. We find that disc occultation is primarily governed by the viewing inclination and can significantly reshape pulse profiles at moderate to high inclinations. Using synthetic Neutron Star Interior Composition Explorer datasets, we investigate parameter recovery for two representative hotspot configurations. For hotspots close to the rotational poles, statistically acceptable fits can yield posteriors that deviate noticeably from the true parameters. In contrast, in a case with hotspots located closer to the equator we find more reliable parameter recovery. We further find that neglecting disc occultation can introduce spurious posterior modes with comparable statistical support, potentially affecting the interpretation of inferred neutron star parameters, suggesting that this effect should be included in accreting millisecond pulsar pulse profile modelling.

We report evidence for a candidate pulsational signal at similar to 0.22 Hz from NGC 7456 ULX-1, a previously identified ultraluminous X-ray source (ULX). The signal is identified in the 2023 XMM-Newton observation using independent timing techniques, including accelerated searches, Zn2 statistics, and an orbital-demodulation analysis designed to restore phase coherence in the presence of binary motion. The candidate pulsation frequency drift within the observation suggests rapid spin evolution driven by accretion torque. We further estimate the surface dipole magnetic field strength to be B similar to 1012-1014 G. These results provide evidence that NGC 7456 ULX-1 may host an accreting neutron star, although confirmation with independent datasets or additional observations is required.

Recent optical astrometric and spectroscopic surveys have identified numerous neutron star (NS) candidates in nonaccreting detached binary systems, but their compact-object nature remains unconfirmed. In this work, we present targeted radio observations of 31 such candidates using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the Robert C. Byrd Green Bank Telescope, and the Shanghai TianMa Radio Telescope. Over a total of 46.65 hr of observing time, we detected neither periodic nor single-pulse radio emissions. These nondetections place stringent upper limits on the flux densities of any potential radio signals, reaching ∼4 μ Jy for periodic emission and ∼10 mJy for single pulses with FAST. Since our observations are highly sensitive and the flux density upper limits are well below the median fluxes of known Galactic pulsars, this suggests that geometric beaming is the most likely explanation for the nondetections if these objects are indeed pulsars. Alternatively, the NSs may be sufficiently old (≳10 Gyr) and have become intrinsically radio-quiet. In this case, our findings highlight the inherent difficulty of confirming NSs in such old detached binary systems through radio pulsation searches.

Magnetization vector inversion is an effective method for analysing magnetic anomaly data influenced by significant remanent magnetization. However, the multidimensional parameters of the magnetization vector increase both the non-uniqueness of the solutions and the computational burden. We propose a magnetization vector inversion method based on Gaussian radial basis function which the magnetization vector parameters are represented by the functional node parameters. By leveraging the inherent smoothness and local support characteristics of Gaussian radial basis function, the method suppresses spurious divergence in magnetization direction during the inversion process, thereby enhancing both the accuracy and computational efficiency of the inversion results. The proposed method is applied to interpret magnetic data in Xiangshan area for revealing the magnetization characteristics of magma-hydrothermal structures. The region of non-uniform magnetization vectors, which can be interpreted as lithological contacts and alteration fronts, may indicate multiple phases of magmatic intrusion. The distinct magnetization directions between shallow mineralized bodies and underlying magma conduits facilitates the identification of potential mineralized rocks and magma conduits that are undetectable by conventional magnetic intensity analysis. Drilling in the study area confirms the presence of Cu-Ni mineralization in the shallow mafic-ultramafic intrusions. Results demonstrate that the magnetization vector inversion could capture complex geological information, providing a promising tool for understanding volcanic and magmatic systems.

Ultraluminous X-ray sources (ULXs) are off-nuclear compact objects with apparent luminosities above 10 ^39 erg s ^−1 , often exceeding the Eddington limit for stellar-mass black holes. Beaming is a commonly invoked mechanism to explain their extreme brightness, and the dependence of the beaming factor on accretion rate is a critical parameter. In this work, we investigate how different beaming prescriptions affect the predicted properties of ULX populations. Using binary population synthesis, we construct synthetic X-ray luminosity functions (XLFs) for both classical and log-modified beaming models at solar and subsolar metallicities. The classical model predicts a larger intrinsic number of bright ULXs, but strong beaming reduces their observable fraction, resulting in fewer visible ULXs compared to the log-modified model. The log-modified prescription yields a shallower slope at high luminosity, aligning better with observed XLFs, and increases the fraction of observable neutron star ULXs above 10 ^39 erg s ^−1 . These results underscore the significant role of the beaming law in shaping ULX statistical distributions and assessing neutron star contributions to the population.

Most massive stars reside in binary systems, and binary interactions can profoundly alter the properties of both stellar components. In young open clusters, such interactions can produce multiple main-sequence populations, despite the coeval nature of the stellar population. In this work, we extend our previous studies on the role of binary evolution in shaping main-sequence morphologies by performing a more detailed and systematic analysis. We investigate the progenitor properties of different main-sequence populations from 10 to 100 Myr using detailed binary models computed with MESA, assuming SMC-like metallicity, and initial primary masses of 3–100 M _⊙ . We provide physical explanations for the features identified in our earlier work. We focus especially on post–Case A mass-transfer systems, which produce a prominent “bridge-like” feature connecting the reddest Be stars and the bluest blue stragglers. We show that the positions of these stars are sensitive to surface helium enrichment and rotation. We further perform quantitative comparisons with observed clusters aged 30–90 Myr whose turn-off masses are from approximately 9 to 5 M _⊙ . We find that our models broadly reproduce the observed stellar distributions. However, we underpredict the fraction of Be stars, suggesting that a larger fraction of binaries may undergo stable mass transfer. We also overpredict the number of stars on the redder side of the unresolved-binary sequence, indicating that the initial mass-ratio distribution may deviate from a flat distribution. Overall, this work provides a comprehensive analysis of how binary evolution produces diverse main-sequence populations and lays the foundation for future population-synthesis studies.

The standard magnetic braking (MB) model has long failed to explain key properties of low-mass X-ray binaries (LMXBs) — including their accretion rates, the formation of ultracompact binaries, and orbital expansion — casting doubt on binary evolution and gravitational-wave progenitor predictions. Phenomenological modifications exist, but a unified, physically grounded mechanism has been missing. Here we show that the overlooked coupling between magnetic saturation and irradiation-driven winds (IDW) provides this missing framework. Accretion-powered irradiation enhances the donor wind, which in turn amplifies MB exactly where needed. Our Saturated MB + IDW (SMB+IDW) model simultaneously resolves three outstanding discrepancies with no fine-tuning: (1) it reproduces the full observed distribution of accretion rates across persistent and transient LMXBs; (2) it naturally explains ultracompact X-ray binary formation; and (3) it quantitatively matches the orbital period distribution of descendant millisecond pulsar (MSP) binaries — a critical independent test failed by all previous models. Critically, the SMB+IDW model transforms MB from an externally imposed condition into a self-consistently regulated process tied to the accretion history. By unifying LMXB evolution to MSPs in a single physical picture, our work resolves the long-standing diversity puzzle and establishes a physics-based foundation for next-generation population synthesis, gravitational-wave progenitor predictions, and compact binary interpretation across cosmic time.

Ultraluminous X-ray pulsars (ULXPs) serve as unique astrophysical laboratories, offering critical insights into accretion physics under extreme conditions, such as strong magnetic fields and super-Eddington accretion rates. Additionally, the nature of pulsars, i.e. the equation of state of supranuclear matter, is still a matter of intense debate, basing on either conventional neutron stars or strange stars. In this work, in order to differentiate the conjectured states of matter, we investigate accretion columns of ULXPs based on the strangeon-star (SS) model, focusing on the thermal mound at the column base. Accounting for Coulomb and strangeness barriers of SSs, we find that the mound can reach 0.7-0.95 km in height with temperatures above 10(9) K, enabling substantial neutrino emission via electron-positron annihilation. At low-accretion rates (< 10(20) g s(-1)), photons dominate the luminosity, while at higher rates (>10(21 )g s(-1)), photon trapping makes neutrino emission the main cooling channel, with total luminosity exceeding photon emission, which saturates near 10(41)ergs(-1). Even though the predicted neutrino flux from the nearest system, Swift J0243.6+6124, lies well below the diffuse MeV background - implying that detectable emission would require substantially closer or more luminous sources - these results demonstrate the key role of the thermal mound and SS properties in accretion, providing a foundation for future ULXP studies and suggesting that neutrino observations could, in principle, offer a novel probe of SSs and extreme supranuclear matter.

We present a systematic study of the evolution of low- and intermediate-mass X-ray binaries consisting of a 1.4 M _⊙ neutron star (NS) and a donor star of mass 1–8 M _⊙ . Using grids of detailed MESA simulations, we show that for donor masses of 2–8 M _⊙ , mass transfer may be dynamically unstable, leading to a common envelope (CE) phase. By adopting CE ejection efficiencies in the range α _CE = 0.3–3.0, we find that post-CE binaries frequently experience a CE decoupling phase (CEDP), which plays a critical role in determining their final orbital and compositional properties. Systems with initial donor masses ≳3.5 M _⊙ predominantly evolve into NS binaries with carbon–oxygen or oxygen–neon white dwarfs (WDs) with masses between 0.5 and 1.4 M _⊙ . Comparison with the observed population of binary pulsars with a WD companion shows better agreement with higher CE ejection efficiencies ( α _CE = 3.0). Furthermore, we demonstrate that NSs can accrete a sufficient amount of matter (≳0.01 M _⊙ ) during the CEDP and subsequent Case BA/BB/BC mass transfer phases to be effectively recycled into millisecond pulsars. We identify two distinct evolutionary channels capable of reproducing the observed characteristics of the millisecond pulsar PSR J1928+1815 with a helium-star companion. Our results highlight the importance of the CEDP in the formation of recycled pulsars and provide constraints on the CE ejection efficiency during binary evolution.