arXiv subjects

Xiangcun Meng

Publications and source records attributed to Xiangcun Meng.

At least 19 recordsLinked to original sources

arXiv2026

A Helium-shell Burning Blue Horizontal Branch Star Produced from Common Envelope Evolution

Observationally, blue horizontal branch (BHB) stars are defined as hot stars occupying a characteristic region between the extreme blue horizontal branch and RR Lyrae variables in the Hertzsprung-Russell diagram. Most of them are interpreted as stripped core-helium-burning stars, but the role of binary interaction in their formation remains unclear. Here, we report the discovery of a metal-rich BHB star in a 0.82628-day binary system (Feige 64) comprising a $0.35\pm0.03\,M_{\odot}$ BHB star and a likely $1.26\pm0.17\,M_{\odot}$ white dwarf (WD). The BHB star has an effective temperature of $15{,}524\pm310$ K and a luminosity of $39.7\pm4.1\,L_{\odot}$. Stellar evolution modelling indicates that it is a helium-shell-burning star produced through the common-envelope channel, retaining a hydrogen-rich envelope that is more massive than previously thought for low-mass stars. This finding provides direct evidence for binary interaction in the formation of BHB stars, offering a fresh perspective on interpreting this emerging population.

astro-ph.SR↗

arXiv2026

Environmental dependence of Type Ia supernova standardization on the local luminosity-weighted age

Context. The dependence of Type Ia supernova (SNe Ia) standardized luminosity on host galaxy properties constitutes a significant systematic error in cosmology. However, the widely used empirical mass step, acting as an indirect global proxy, obscures the direct physical link to the progenitor environment, thereby limiting the precision of SNe Ia luminosity standardization. Aims. We investigate the fundamental origin of these dependencies by comparing local luminosity-weighted age (LWA) with global mass, testing whether the mass step is a proxy for progenitor age. Methods. Using SDSS-MaNGA Pipe3D, we measure local LWA within a 1 kpc aperture for 56 SNe Ia and perform a joint likelihood analysis to separate the effects of local age and mass on Hubble residuals. Results. SNe Ia in younger environments are significantly fainter than those in older environments, showing an age step of 0.163 mag (5.2-sigma) after standardization. Although global and local mass steps are initially detected (0.071 mag, 2.0-sigma and 0.087 mag, 2.4-sigma, respectively), both become insignificant after accounting for age. The global mass step decreases to 0.028 mag (0.9-sigma), while the age step remains 0.156 mag (4.9-sigma). Similarly, the local mass step decreases to 0.012 mag (0.3-sigma), whereas the age step remains 0.157 mag (4.4-sigma). Including the local LWA age step reduces the Hubble residual dispersion (wRMS) from 0.1550 to 0.1376 mag. Conclusions. Our results provide strong evidence that approximately 50%-60% of the variance from the stellar mass step is due to an environmental dependence on progenitor age. A systematic bias in the dark energy equation of state parameter could be introduced if the age-dependent luminosity evolution is neglected, highlighting the necessity of local age corrections for next-generation cosmology.

astro-ph.CO↗

arXiv2026

SN 2022erq: A Superluminous Thermonuclear Supernova with Escalating Preexplosion Mass Loss

We present a photometric and spectroscopic study of the superluminous Type Ia supernova SN 2022erq. Its early spectra, dominated by iron-group elements with weak intermediate-mass features, might indicate highly efficient nuclear burning, broadly similar to that inferred for some overluminous SNe Ia. The rapid emergence and persistence of narrow Balmer emission lines superposed on this iron-rich spectrum provide clear evidence of long-lived interaction with a hydrogen-rich circumstellar medium (CSM), establishing SN 2022erq as a member of the rare Ia-CSM class. SN 2022erq reached a peak bolometric luminosity of about 8 x 10^43 erg/s and exhibited an exceptionally slow post-peak decline, indicating that its light curve is dominated by long-duration ejecta-CSM interaction. By combining H-alpha diagnostics with bolometric light-curve modeling, we reconstruct the pre-explosion mass-loss history of the progenitor. The mass-loss rate escalated by one order of magnitude over the final decades, rising from about 0.04 to about 0.6 solar masses per year. This surge produced a massive, extended CSM shell of about 3 solar masses out to about 3.5 x 10^16 cm. The young stellar environment (about 100 Myr) together with this substantial, extensive CSM points to a progenitor system consisting of a white dwarf and an intermediate-mass companion that underwent increasing mass loss prior to explosion.

astro-ph.HE↗

arXiv2026

Revisiting atmospheric Roche lobe overflow in symbiotic binaries

Classical binary evolution models predict dynamically unstable mass transfer in symbiotic stars with high mass ratios, leading to a common envelope. However, many observed S-type symbiotic systems show long-lived interaction, suggesting that an additional stabilizing mechanism may be at work. We investigate whether atmospheric Roche-lobe overflow can prolong the mass-transfer phase and help reconcile theory with observations. We implement the Rapid Unified Mass Transfer framework in \texttt{MESA} and compute a grid of white-dwarf--giant binaries covering a wide range of donor masses, mass ratios, and orbital periods. We then compare the resulting lifetimes and evolutionary tracks with well-constrained Galactic S-type symbiotic systems. For convective giant donors, our models recover stable mass transfer up to $q \simeq 1.5$, while atmospheric overflow strongly extends the symbiotic phase. RGB and early-AGB systems with $q \lesssim 1.5$ can remain interacting for up to $10^6$ yr at $\dot{M} \gtrsim 10^{-9},M_{\odot},{\rm yr}^{-1}$, much longer than the commonly assumed $\sim 10^3$ yr pre-common-envelope lifetime. In these systems, the orbit shrinks mildly and may re-expand after mass-ratio reversal. Systems with higher mass ratios still evolve toward a common envelope, but even for $q \simeq 2$--$4$ the symbiotic phase can last $10^4$--$10^5$ yr. The synthetic distribution in the orbital-period--mass-ratio plane and individual evolutionary tracks are broadly consistent with observed S-type symbiotic binaries, including recurrent novae. The RUMT framework, which incorporates atmospheric RLOF, provides an explanation for the long-term stability of many symbiotic binaries and may account for their high observed occurrence rate.

astro-ph.SR↗

arXiv2026

Unraveling the mysteries of supernovae with SKA+VLBI

Supernovae (SNe) drive cosmic chemical enrichment and shape galactic feedback, yet the link between progenitors and explosion outcomes remains poorly constrained because the earliest phases are rarely resolved. Radio emission traces synchrotron radiation where the fastest ejecta interact with the circumstellar medium (CSM), providing a uniquely penetrating probe of these phases. SKA-Mid phased into global VLBI will move from simple detections to routine interferometric imaging of nearby extragalactic SNe. Sub-$\mu$Jy sensitivity and mas-scale SKA+VLBI imaging, complemented by visibility-domain model fitting for sub-beam radius measurements at 5-15 GHz will allow us to follow the expanding shocks of stripped-envelope SNe out to $\sim$25 Mpc, measure deceleration indices ($m$) and axial ratios to $\approx 5-10\%$, and directly test jet-assisted versus neutrino-driven explosion mechanisms. For interacting SNe (Type IIn/Ibn), SKA+VLBI will resolve clumpy and toroidal CSM on progenitor scales, constraining the timing and geometry of eruptive pre-explosion mass loss. Deep limits on Type Ia SNe will tightly restrict the allowed single-degenerate parameter space, while late-time imaging will search for nascent compact remnants and pulsar wind nebulae. In synergy with optical, X-ray and gravitational wave facilities, SKA+VLBI will turn nearby SNe into laboratories for time-resolved shock physics and progenitor mapping.

astro-ph.HE↗

arXiv2026

Formation of Extremely Low-mass White Dwarf Binaries Undergoing Enhanced Angular Momentum Loss

Extremely low-mass white dwarfs (ELM WDs) are helium (He) WDs with masses below $\sim 0.3\ M_{\odot}$, mainly formed through binary interaction. ELM WD binaries typically are formed from two channels, namely the stable Roche lobe overflow (RLOF) channel and the common envelope ejection channel. For ELM WD binaries produced from RLOF channel, the ELM WD mass has a strong correlation with the orbital period, i.e., the so-called WD mass-orbital period relation. However, the observations in the ELM Survey show that the orbital periods of ELM WD binaries from the RLOF channel are typically shorter than the theoretically predicted values. Extra angular momentum loss (AML) may be needed to explain such a phenomenon. In this work, we assumed that part of the transferred mass from the donor is lost at the outer Lagrangian point and simulated the formation of ELM WD binaries. Enhanced AML enables more mass to be lost during thermal-timescale mass transfer, thereby affecting nuclear burning in the transfer phase and producing ELM WDs with distinct internal structures. These structural differences alter the (pre-)He WD mass-radius relation at the end of mass transfer, which in turn shifts the WD mass-orbital period relation downward. These adjustments enable our model to successfully reproduce the majority of observed systems from the relevant survey projects.

astro-ph.SR↗

arXiv2026

Using Lithium and Beryllium to Study Structure and Evolution of Rotating Stars: Spite Plateau of Halo Stars

The observed lithum (Li) abundance of Galactic halo stars mainly fall within the range of 2.0--2.4 dex. This nearly constant value, known as the Spite plateau, is approximately a factor of three lower than the value predicted from cosmic microwave background measurements and standard Big Bang Nucleosynthesis (BBN) calculations. This discrepancy -- referred to as the cosmological Li problem -- is considered a potential indication of new physics or astrophysical processes. We employed models incorporating gravitational settling, diffusion, rotation, and magnetic fields to explain the Spite plateau. The rotating models predict that Li abundances in stars with ages of roughly 8--13 Gyr and effective temperatures between 6400 and 5900 K generally fall within 2.0--2.4 dex, forming a well-defined Li plateau, followed by a sharp decline in Li abundance down to about 5200 K. The Li plateau results from the combined effects of variations in convection zone depth, gravitational settling, diffusion, rotation, and magnetic fields. For red giant branch stars with $T_{\mathrm{eff}} \lesssim$ 5200 K, the rotating models predict another Li plateau with an abundance of about 1.0 dex. These results are in good agreement with observations. Moreover, the initial Li abundance of 2.72 dex adopted in the models matches the BBN prediction, implying that the Li problem arises from stellar Li depletion. Furthermore, the rotating models also reproduce the Li and Be distributions of the sample that exhibit the Spite plateau meltdown and Be deviation.

astro-ph.SR↗

arXiv2026

Dynamical Mass Loss at the End of TP-AGB stars

The thermally pulsating asymptotic giant branch (TP-AGB) phase plays a key role in the evolution of low- to intermediate-mass stars, driving mass loss that influences their final stages and contributes to galactic chemical enrichment. However, the mechanisms behind mass loss, particularly at the end of AGB, are still not well understood. We aim to investigate the relationship between stellar parameters and envelope dynamics during the TP-AGB phase, evaluating whether dynamical instabilities in the envelope can act as a possible mass-loss mechanism. We use hydrodynamics method in MESA to simulate the dynamical pulsations and resulting mass loss during the TP-AGB phase of a star evolved from a 1.5 Msun zero-age main sequence. Our simulations reproduce the dynamical pulsation behavior of stars during the TP-AGB phase, demonstrating that the envelope mass is a key factor governing pulsational properties. As the envelope mass decreases, both the pulsation period and radial amplitude increase, consistent with observational trends. For 1.5 Msun model, once the envelope mass declines to approximately 0.25 Msun, the model enters a regime of violent pulsations, potentially ejecting the remaining envelope within a few hundred years. We suggest that the instability can act as the dominant mass-loss mechanism in the end of the TP-AGB phase, marking a rapid transitional stage toward the post-AGB phase.

astro-ph.SR↗

arXiv2025

Irradiation-Driven Formation of Supersoft X-ray Sources Following Classical Novae

Supersoft X-ray sources (SSSs) are characterized by persistent thermonuclear burning on the surfaces of white dwarfs (WDs).The standard model requires high mass transfer rates of $\sim 10^{-7}\, {\rm M_{\odot}}\,yr^{-1}$ from massive companions, presenting a theoretical impediment to the observed short-period SSSs, whose orbital periods imply low-mass donors theoretically incapable of sustaining such accretion.To resolve this paradox,we propose and demonstrate through detailed simulations that irradiative feedback following a classical nova (CN) eruption provides a natural formation channel.Through detailed binary evolution simulations with MESA, we reveal that sustained WD irradiation initially from the outburst and subsequently from accretion luminosity triggers significant and stable expansion of the low mass companion.This,in turn,drives mass-transfer rates into the stable hydrogen-burning regime and sustains it beyond $10^4$ years after the initiation of hydrogen burning.This mechanism robustly explains the observed population of short-period SSSs. Moreover,when irradiation-driven mass transfer rate drops below the stable accretion rate,it may lead to the rapid accumulation of sufficient material on shorter time scales to trigger a recurrent nova outburst instead of SSS, thereby also offering an explanation for the origin of short-period recurrent novae.

astro-ph.HE↗

arXiv2025

The fractions of reflection effect systems detected in different subclasses of hot subdwarfs

Hot subdwarfs with close low-mass M-type or brown dwarf companions usually show the reflection effect and often also eclipses. Through inspecting the light variations, we estimate the fractions of reflection effect systems detected in different subclasses of hot subdwarfs and constrain their possible formation channels. We noticed that none of the helium-rich hot subdwarfs were found with the reflection effect. Most of them might form through the merger channel. About 13\% of the He-poor hot subdwarfs on the extreme horizontal branch (EHB) with $T_{\rm eff}$ $\sim$ 25,000 -- 33,000 K are discovered with the reflection effect. Nevertheless, the cooler hot subdwarfs located on the top of the EHB, those grouped on the bottom of the EHB, and those located above the EHB with $T_{\rm eff}$ $\sim$ 45,000 -- 75,000 K exhibit lower fractions of reflection effect systems of about 2\%. These three subclasses of hot subdwarfs might contain higher fractions of single stars. Hot subdwarfs below the EHB also show a low fraction of reflection effect systems. They might have a higher fraction of stars with close WD companions. A similar fraction of reflection effect systems to those on the EHB with $T_{\rm eff}$ $\sim$ 25,000 -- 33,000 K is found in hot subdwarfs located above the EHB with $T_{\rm eff}$ $\sim$ 35,000 -- 45,000 K. We also discovered that hot subdwarfs close to the Galactic Plane might have a higher fraction of stars with the reflection effect than those at higher latitudes.

astro-ph.SR↗

arXiv2025

Millisecond Pulsars in M2: New discoveries and a detailed timing analysis

Globular clusters (GCs) offer a unique environment for discovering and studying millisecond pulsars. In this paper, we present a multi-epoch search and detailed timing analysis of millisecond pulsars in the GC M2, using the Five-hundred-meter Aperture Spherical Telescope. We have discovered two new binary millisecond pulsars in M2, designated M2F and M2G, respectively. We provide measurements of the emission properties of all known pulsars in M2, including their polarization profiles, rotation measures, flux densities, scintillation characteristics, and so forth. In particular, we report the first rotation measure at the distance and direction of this cluster. Additionally, we report the first phase-coherent timing solutions for the M2 pulsars. From our Bayesian timing analysis, we have measured their spin and orbital parameters with high precision, including the advance of periastron for M2A and M2E indicating total system masses of 1.75(13) and 1.80(5) solar masses respectively. Using archival data from the Hubble Space Telescope, we have identified an optical counterpart of M2C, which is likely the white dwarf companion of the pulsar. By combining results from optical and radio observations, we have reconstructed the binary evolution track of this system and estimated the cooling age of the companion to be approximately 10\,Myr, making it the youngest white dwarf in any known GC binary pulsars. Furthermore, using the spin period derivatives of M2 pulsars, we have investigated the gravitational potential of the cluster and found that our results strongly support the latest central-stellar-velocity dispersion measurement in M2.

astro-ph.HE↗

arXiv2025

SN 2024gy: Multi-epoch Spectroscopic Features Suggestive of Delayed Detonation in a Type Ia Supernova

We present photometric and spectroscopic observations of SN 2024gy, a Type Ia supernova (SN Ia) exhibiting high-velocity features (HVFs) in its early-time spectra. This SN reaches a peak $B$-band magnitude of $-19.25 \pm 0.29$ mag and subsequently declines by $\Delta m_{15}(B) \approx 1.12$ mag, consistent with the luminosity-width relation characteristic of normal SNe Ia. Based on the peak thermal luminosity of $(1.2 \pm 0.3) \times 10^{43}$ erg s$^{-1}$, we estimate that $0.57 \pm 0.14~\rm M_{\odot}$ of $^{56}$Ni was synthesized during the explosion. Our dense early spectral monitoring revealed significant velocity disparities within the ejecta. Notably, absorption features from the Ca II near-infrared triplet were observed at velocities exceeding 25,000 km s$^{-1}$, while the Si II $\lambda$6355 line velocity at the same epoch was significantly lower at $\sim$ 16,000 km s$^{-1}$. This velocity disparity likely reflects distinct ionization states of intermediate-mass elements in the outermost layers. The prominent Ca II HVFs may originate from ionization suppression within the highest-velocity ejecta, potentially indicative of minimal hydrogen mixing in a delayed-detonation explosion scenario. Additionally, the Ni/Fe ratio derived from the nebular spectrum of SN 2024gy provides further support for this model.

astro-ph.HE↗

arXiv2025

Impact of convective overshooting on the single-degenerate model of Type Ia supernovae

The single-degenerate (SD) model is one of the principal models for the progenitors of Type Ia supernovae (SNe Ia). However, it faces some challenges, the primary being its inability to account for the observed SN Ia birth rate. Many studies have attempted to address this issue by expanding the parameter space, defined by the initial donor star mass and orbital period, that can lead to SNe Ia, as well as by improving binary population synthesis. While these efforts have led to significant progress, many uncertainties in stellar physics persist, which influences the outcomes of such studies. Convective overshooting, which can significantly affect the internal structure of a star and subsequently its evolution within a binary system, is one of the most significant sources of uncertainty in stellar physics. We investigate the effect of convective overshooting on the parameter space and birth rate of SNe Ia within the SD model. We employed the common-envelope wind (CEW) model, a new version of the SD model, as our progenitor model. Using MESA, we obtained the parameter space that leads to SNe Ia for three different convective overshooting parameters and calculated the corresponding SN Ia birth rate. Convective overshooting expands the upper boundaries (corresponding to a larger initial donor mass) and right boundaries (corresponding to a longer initial orbital period) of the parameter space for systems with massive white dwarfs (WDs; >= 0.75Msun). However, the minimum WD mass and the parameter space for low-mass WDs - and, consequently, the calculated SN Ia birth rate - vary non-monotonically with convective overshooting parameters. The CEW model may explain the SNe Ia that interact with the circumstellar medium (CSM), i.e., SNe Ia-CSM. We find that the parameter space for SNe Ia-CSM increases with convective overshooting parameters, as does their birth rate.

astro-ph.SR↗

arXiv2025

Huntsman may need to be irradiated

Millisecond pulsars are rapidly rotating neutron stars, and it is now widely accepted that their extremely short rotation periods result from the accretion of material from a companion star. Binary evolution theory predicts that millisecond pulsars can have various types of companion stars. However, in observations, binary pulsars with giant companions, referred to as ``huntsman pulsars'', are extremely rare. Following the initial discovery of the first huntsman pulsar, 1FGL J1417.7-4407, a second huntsman millisecond pulsar binary, PSR J1947-1120, has been recently reported approximately a decade later. In this paper, we model the formation and evolution of two huntsman pulsars. Our model with the irradiation effect can explain the observed properties of huntsman pulsar binaries and suggests that if the irradiation effect is considered, the companion star may be a normal red giant star, rather than just a red bump star.

astro-ph.SR↗

arXiv2025

Eccentric millisecond pulsar + subdwarf B star from rotationally delayed accretion-induced-collapse scenario

Eccentric millisecond pulsar + helium white dwarf (MSP + He WD) systems have attracted increasing attention, with the rotationally delayed accretion-induced collapse (RD-AIC) scenario proposed as a possible formation channel. Given the similarity between the formation channels of He WDs and subdwarf B (sdB) stars, eccentric MSP + sdB binaries could also exist in the Galaxy, though none have been detected so far. Theoretical predictions of their properties would greatly aid in their discovery. Here, within the RD-AIC framework, I present predictions for their orbital parameters, including MSP mass, secondary mass, eccentricity and orbital period. Based on two detailed binary population synthesis calculations, I estimate their Galactic birth rate to be $(0.67-1.5)\times10^{\rm -4}~{\rm yr^{\rm -1}}$. Then, a very conservative upper limit for their total number in the Galaxy is 15000, implying that the most optimistic fraction of eccentric MSP + sdB systems among all MSP + sdB populations could reach up to 55\%. These systems are relatively young, with ages on the order of a few hundred Myr, and should therefore be found in relatively young environments. Furthermore, most MSPs in such eccentric binaries have masses below 1.5 $M_{\odot}$. I also briefly discuss their potential future applications in various astrophysical context.

astro-ph.HE↗

arXiv2025

Producing type Ia supernovae from hybrid CONe white dwarfs with main-sequence binary companions at low metallicity of Z = 0.0001

The nature of progenitors of Type Ia supernovae (SNe Ia) and their explosion mechanism remain unclear. It has been suggested that SNe Ia may be resulted from thermonuclear explosions of hybrid carbon-oxygen-neon white dwarfs(CONe WDs) when they grow in mass to approach the Chandrasekhar mass limit by accreting matter from a binary main-sequence (MS) companion. In this work, we combine the results of detailed binary evolution calculations with population synthesis models to investigate the rates and delay times of SNe Ia in the CONe WD + MS channel at low metallicity environment of Z = 0.0001. For a constant star formation rate of 5 M_sun yr-1, our calculations predict that the SN Ia rates in the CONe WD + MS channel at low metallicity of Z = 0.0001 is about 0.11 - 3.89 * 10-4 yr-1. In addition,delay times in this channel cover a wide range of 0.05 - 2.5 Gyr. We further compare our results to those given by previous study for the CONe WD + MS channel with higher metallicity of Z = 0.02 to explore the influence of metallicity on the results. We find that these two metallicity environments give a slight difference in rates and delay times of SNe Ia from the CONe WD + MS channel, although SNe Ia produced at low metallicity environment of Z = 0.0001 have relatively longer delay times.

astro-ph.SR↗

arXiv2025

Formation and evolution of new primordial open cluster groups: Feedback-driven star formation

The formation mechanisms of open cluster (OCs) groups remain unclear due to limited sample sizes and data precision. Recent advancements in Gaia astrometric data provide an unprecedented opportunity to study OC groups in greater detail. This study aims to extend the sample of OC groups and investigate their formation and evolution mechanisms, with a focus on the role of stellar feedback in triggering star formation. We identify four new OC groups based on Gaia data, whose member OCs are spatially proximate and kinematically coherent. Their age spreads are consistent with the timescale of continuous star formation, suggesting that their member OCs formed sequentially from the same molecular cloud. N-body simulation results further reveal that these groups will gradually disperse, evolving into independent OCs. By analyzing the correlation between OC ages and their separation from potential SN explosion sites, we predict SN explosion regions around the birthplaces of OC groups. The strong correlation between OC ages and predicted SN explosion sites supports a supernova-triggered star formation scenario. Additionally, we trace pulsar (PSR) orbits to examine their association with these regions. We detected three PSRs near Group 1 and 26 PSRs near Group 2, whose birthplaces align with the predicted SN explosions regions. The presence of PSRs associated with OC groups provides additional observational evidence for SN explosions in this region, further supporting a supernova-triggered star formation scenario for G1 and G2. We propose that multiple SN explosions in a short period triggered the formation of Group 1 and Group 2, reinforcing the hierarchical star formation model. These results highlight the multi-scale interactions driving star and OC formation and provide new insights into the role of stellar feedback in shaping OC groups.

astro-ph.GA↗

arXiv2024

Radial velocity variability fractions of different types of hot subdwarf stars

Different types of hot subdwarfs may have different origins, which will cause them to present different radial velocity (RV) variability properties. Only 6$\pm$4% of our single-lined He-rich hot subdwarfs that only show spectroscopic features of hot subdwarfs are found to be RV variable, which is lower than the fraction of single-lined He-poor sdB stars (31$\pm$3%). Single-lined sdB stars with effective temperatures ($T_{\rm eff}$) $\sim$ 25,000 $-$ 33,000 K show an RV-variability fraction of 34$\pm$5%, while lower RV-variability fractions are observed for single-lined sdB stars cooler than about 25,000 K (11$\pm$4%), single-lined sdB/OB stars with $T_{\rm eff}$ $\sim$ 33,000 $-$ 40,000 K and surface gravities about 5.7 $-$ 6.0 (13$\pm$3%), as well as single-lined sdO/B stars with $T_{\rm eff}$ $\sim$ 45,000 $-$ 70,000 K (10$\pm$7%). Single-lined hot subdwarfs with $T_{\rm eff}$ $\sim$ 35,000 $-$ 45,000 K located above the extreme horizontal branch (EHB) show a similar RV-variability fraction of 34$\pm$9% as single-lined sdB stars at about 25,000 $-$ 33,000 K. The largest RV-variability fraction of 51$\pm$8% is found in single-lined hot subdwarfs below the canonical EHB. The detected RV-variability fraction of our composite hot subdwarfs with an infrared excess in their spectral energy distributions is 9$\pm$3%, which is lower than that fraction of single-lined hot subdwarfs. Since the average RV uncertainty we measured in the LAMOST spectra is about 7.0 km/s, the lower detected RV-variability fraction for composite hot subdwarfs is expected because the RV amplitudes associated with long-period systems are lower.

astro-ph.SR↗