arXiv subjects

Chenyu He

Publications and source records attributed to Chenyu He.

12 recordsLinked to original sources

arXiv2026

Gravity-mode main-sequence pulsators in the open clusters NGC 3532 and NGC 2516: Instability strip, near-core rotation, and internal structure

Context. Studying pulsating stars in clusters opens a new window onto stellar physics. Gravity-mode (g-mode) pulsators in open clusters allow us to measure their near-core rotation rates and, together with cluster age and mass constraints, test angular momentum transport in stars above about 1.5 solar masses. Aims. We aim to detect g-mode pulsations in member stars of the young open cluster NGC 3532, about 300 Myr old, and to measure their near-core rotation rates and internal properties. Methods. We used TESS photometry to extract light curves of NGC 3532 members. The observed g-mode period spacings allow us to measure near-core rotation rates and the asymptotic period spacing, Pi0. We also fitted isochrones to the colour-magnitude diagrams of NGC 3532 and NGC 2516 to refine the cluster ages and obtain stellar masses. Results. We constrain the observed instability region of young gamma Doradus members from a blue edge at about 7760 K to a red edge at about 7070 K, while some hotter g-mode pulsators are also seen. The near-core rotation rates show a rotation-mass relation similar to that in NGC 2516: below 1.6 solar masses, the rotation rate increases with mass, whereas above 1.6 solar masses the NGC 3532 stars reach a plateau at about 2.8 d^-1. This mass may mark a threshold between different rotational spin-down mechanisms. Existing evolutionary models with angular momentum transport imply that these g-mode pulsators were born rotating above 55 percent of the critical value. Our simplified models, assuming spherical symmetry, angular momentum conservation, and rigid internal rotation, suggest that either mass-dependent initial rotation rates are required, or that minor angular momentum loss still operates above 1.6 solar masses. Finally, our Pi0 measurements reveal a discrepancy with theoretical predictions for some pulsators, as also found in the younger cluster NGC 2516.

astro-ph.SR↗

arXiv2026

Token Economics for LLM Agents: A Dual-View Study from Computing and Economics

As LLM agents evolve, tokens have emerged as the core economic primitives of Agentic AI. However, their exponential consumption introduces severe computational, collaborative, and security bottlenecks. Current surveys remain fragmented across system optimization, architecture design, and trust, lacking a unified framework to evaluate the fundamental trade-off between output quality and economic cost. To bridge this gap, this survey presents the first comprehensive survey of Token Economics. By unifying computer science and economics, we conceptualize tokens as production factors, exchange mediums, and units of account. We synthesize existing literature across a four-dimensional taxonomy: (1) Micro-level (Single Agent): Optimizing budget-constrained factor substitution via neoclassical firm theory. (2) Meso-level (Multi-Agent Systems): Minimizing collaboration friction using transaction cost and principal-agent theories. (3) Macro-level (Agent Ecosystems): Addressing congestion externalities and pricing via mechanism design. (4) Security: Internalizing adversarial threats as endogenous economic constraints. Finally, we outline frontier directions, including differentiable token budgets and dynamic markets, to lay the theoretical foundation for scalable next-generation agent systems.

cs.AI↗

arXiv2026

Tidal Synchronization of Binaries in Pleiades

Tidal interactions in close binaries play a key role in the long-term rotational and orbital evolution. The distributions of circularization across open clusters (OCs) place strong observational constraints on tidal dissipation in binaries. However, direct observational constraints on synchronization among binaries in OCs remain limited. For the 125 Myr OC Pleiades, this work combines cluster membership from Gaia Data Release 3, rotation periods from the K2 mission, and orbital solutions of the binary population from a long-term spectroscopic survey, to investigate the degree of tidal synchronization in each binary by comparing the pseudo-synchronization period to the rotation period of the primary stars. Among 42 binaries with reliable orbital periods Porb and rotation periods, we identify seven tidally synchronized systems with Porb < 8.6 days, including one early-type system and six late-type systems. For binaries with longer Porb, primaries generally are super-synchronized, and most systems are eccentric. We find a synchronization transition near Porb ~ 8.6-14 days, comparable to the known circularization period (Porb ~ 7.2 days) in the Pleiades, which suggests similar critical period scales for synchronization and circularization in this coeval population. Synchronization depends much more strongly on mass ratio than on primary mass. Most synchronized systems in Pleiades have high mass ratios and are likely to evolve into double white dwarf systems. Tides likely impose strong rotational braking on close early-type binaries, while their influence on late-type close binaries is weaker, and their spins largely follow the single-star sequence.

astro-ph.SR↗

arXiv2026

Searching for White Dwarf Candidates Formed Through Binary evolution in Star Clusters

White dwarfs (WDs), the evolutionary endpoints of most stars, can form through both single-star and binary channels. While single-star evolutionary models enable reliable WD age estimates, binary evolution introduces interactions that can accelerate WD formation and result in a variety of exotic WDs, which may exhibit strong magnetic fields, rapid rotation, or even serve as potential gravitational wave sources. Such systems offer valuable insights into magnetic field generation, angular momentum evolution, and compact object physics. Star clusters, with their approximately coeval populations, allow precise age determination of member WDs. If a WD's total age derived from single-star evolution exceeds that of its host cluster, it likely indicates a binary origin. In this study, we use \textit{Gaia} 5D astrometry to identify 439 WD candidates in 117 open clusters, with 244 likely formed via binary evolution. We discuss the possibility of dynamical ejection for WDs meeting only 2D (proper motion space) membership criteria. Spectroscopic observations further reveal a subset with strong magnetic fields and rapid rotation, supporting their binary evolutionary origin.

astro-ph.SR↗

arXiv2025

GRATE: a Graph transformer-based deep Reinforcement learning Approach for Time-efficient autonomous robot Exploration

Autonomous robot exploration (ARE) is the process of a robot autonomously navigating and mapping an unknown environment. Recent Reinforcement Learning (RL)-based approaches typically formulate ARE as a sequential decision-making problem defined on a collision-free informative graph. However, these methods often demonstrate limited reasoning ability over graph-structured data. Moreover, due to the insufficient consideration of robot motion, the resulting RL policies are generally optimized to minimize travel distance, while neglecting time efficiency. To overcome these limitations, we propose GRATE, a Deep Reinforcement Learning (DRL)-based approach that leverages a Graph Transformer to effectively capture both local structure patterns and global contextual dependencies of the informative graph, thereby enhancing the model's reasoning capability across the entire environment. In addition, we deploy a Kalman filter to smooth the waypoint outputs, ensuring that the resulting path is kinodynamically feasible for the robot to follow. Experimental results demonstrate that our method exhibits better exploration efficiency (up to 21.5% in distance and 21.3% in time to complete exploration) than state-of-the-art conventional and learning-based baselines in various simulation benchmarks. We also validate our planner in real-world scenarios.

cs.RO↗

arXiv2024

Fast-rotating A- and F-type stars with H{\alpha} emissions in NGC 3532, candidate UV-dim stars?

Extended main-sequence stars that are dim in the ultraviolet passbands of Hubble Space Telescope (UV-dim stars) are found in several young and intermediate-age Magellanic Cloud star clusters. The obscuring of the dust in the discs of stars expelled due to fast rotation have been suggested to be responsible for the appearance of UV-dim stars, and play an important role in the formation of extended main-sequences. In this paper, we report a population of A- and F-type stars who show H{\alpha} emission features in their spectra in a young (~ 340 Myr-old) Galactic neighboring star cluster NGC 3532. By fitting the observed absorption profiles, we found that most H{\alpha} emitters are fast rotating stars, indicating that they form decretion discs by fast rotation like Be stars. As A- and F-type stars dominate the extended main-sequence turn-off regions of intermediate-age clusters, their appearance provides observational evidence to support the dust extinction scenario for these clusters, and might be the counterparts of UV-dim stars that are detected in remote Magellanic Cloud star clusters like NGC 1783.

astro-ph.SR↗

arXiv2024

Disk-Locking Regulates Stellar Rotation in Young Clusters: Insights from NGC 2264

Many young clusters possess extended main sequences, a phenomenon commonly ascribed to stellar rotation. However, the mechanism behind their very wide stellar rotation distributions remains unclear. A proposed explanation is that magnetic star-disk interaction can regulate stellar rotation, i.e., protostars with longer disk lifetimes will eventually evolve into slow rotators, and vice versa. To examine this hypothesis, we took the star forming region, NGC 2264, as a test bed. We have studied its high-mass pre-main-sequence and zero-age main-sequence stars. We found that on average, disk-less pre-main-sequence stars rotate faster than their disk-bearing counterparts. The stellar rotation distribution of its zero-age main-sequence stars is similar to evolved young clusters. We conclude that disk-locking may play a crucial role in the rotational velocity distribution of intermediate-mass early-type stars. We suggest that the observed wide stellar rotation distribution in many young clusters can occur in their early stages.

astro-ph.SR↗

arXiv2024

On the roles of stellar rotation and binarity in NGC 2423's main-sequence turnoff region

Research has shown that many young and intermediate-age clusters (younger than $\sim$2 Gyr) have extended main sequences and main-sequence turnoffs (eMSTOs), which cannot be adequately described by a single isochrone. The reason for the extended main sequences is now known, with the most probable cause being the fast rotation of stars. However, a significant fraction of slowly rotating stars form a younger stellar population than their fast-rotating counterparts, leading to speculation that they have undergone thorough rotational mixing processes internally. One speculation is that a considerable number of slowly rotating stars reside in close binary systems, where tidal forces from companion stars are the cause of their rotational deceleration. In this work, we report a relatively old open star cluster in the Milky Way, NGC 2423 ($\sim$1 Gyrs old), which exhibits an apparent eMSTO. As anticipated, many characteristics of NGC 2423 indicate that its eMSTO is driven by stellar rotations. Our calculations indicate that if slowly rotating stars commonly have a close companion star, they should exhibit significant differences in radial velocities observationally, and binary systems that can be tidally locked within the age of NGC 2423 should have a mass ratio close to 1. However, none of these predictions align with our observations. Interestingly, among the only two equal-mass binary systems in the observed region for which spectroscopic data could be obtained, we discovered that one of them is a tidally locked binary system. This further suggests the validity of our numerical simulation results.

astro-ph.SR↗

arXiv2023

The role of tidal interactions in the formation of slowly rotating early-type stars in young star clusters

The split main sequences found in the colour-magnitude diagrams of star clusters younger than ~600 Myr are suggested to be caused by the dichotomy of stellar rotation rates of upper main-sequence stars. Tidal interactions have been suggested as a possible explanation of the dichotomy of the stellar rotation rates. This hypothesis proposes that the slow rotation rates of stars along the split main sequences are caused by tidal interactions in binaries. To test this scenario, we measured the variations in the radial velocities of slowly rotating stars along the split main sequence of the young Galactic cluster NGC 2422 (~90 Myr) using spectra obtained at multiple epochs with the Canada-France-Hawai'i Telescope. Our results show that most slowly rotating stars are not radial-velocity variables. Using the theory of dynamical tides, we find that the binary separations necessary to fully or partially synchronise our spectroscopic targets, on time-scales shorter than the cluster age, predict much larger radial velocity variations across multiple-epoch observations, or a much larger radial velocity dispersion at a single epoch, than the observed values. This indicates that tidal interactions are not the dominant mechanism to form slowly rotating stars along the split main sequences. As the observations of the rotation velocity distribution among B- and A-type stars in binaries of larger separations hint at a much stronger effect of braking with age, we discuss the consequences of relaxing the constraints of the dynamical tides theory.

astro-ph.SR↗

arXiv2023

On the origin of the split main sequences of the young massive cluster NGC 1856

The detection of split main sequences (MSs) associated with young clusters ($\lesssim$600 Myr) has caught lots of attention. A prevailing scenario is that a bimodality of stellar rotation distribution drives the MS bifurcation. Nevertheless, the origin of the stellar rotation dichotomy remains unclear. Hypotheses involving tidally-locked binaries or blue straggler stars (BSSs) are proposed to explain the observed split MSs. This work examines if the long-term dynamical evolution of star clusters can produce the observed split MSs, through high-performance $N$-body simulation. As a prototype example, the young massive cluster NGC 1856 exhibits an apparent MS bifurcation. Our simulation reports that at the age of NGC 1856, tidally-locked binaries are fully mixed with single stars. This is consistent with the observation that there is no significant spatial difference between blue MS and red MS stars. However, we find that only high mass-ratio binaries can evolve to the tidally-locked phase at the age of the NGC 1856. These tidally-locked binaries will populate a much redder sequence than the MS of single stars rather than a blue MS, which is inconsistent with the hypothesis. The number of tidally-locked binaries cannot account for the observation. Our simulation shows that BSSs produced by binary interactions do populate the blue periphery in the color-magnitude diagram, and their spatial distribution shows a similar pattern of single stars. However, the number of BSSs does not fit the observation.

astro-ph.SR↗

arXiv2022

The role of binarity and stellar rotation in the split main sequence of NGC 2422

In addition to the extended main-sequence turnoffs widely found in young and intermediate-age (~ 600 Myr-2 Gyr-old) star clusters, some younger clusters even exhibit split main sequences (MSs). Different stellar rotation rates are proposed to account for the bifurcated MS pattern, with red and blue MSs (rMS and bMS) populated by fast and slowly rotating stars, respectively. Using photometry from Gaia Early Data Release 3, we report a Galactic open cluster with a bifurcated MS, NGC 2422 ( ~ 90 Myr). We exclude the possibilities that the bifurcated MS pattern is caused by photometric noise or differential reddening. We aim to examine if stellar rotation can account for the split MSs. We use spectra observed with the Canada-France-Hawaii Telescope and the Southern African Large Telescope, and directly measured v sin i, the projected rotational velocities, for stars populating the bMS and rMS. We find that their v sin i values are weakly correlated with their loci in the color-magnitude diagram because of contamination caused by a large fraction of rMS stars with low projected rotational velocities. Based on the spectral energy distribution fitting method, we suggest that these slowly rotating stars at the rMS may hide a binary companion, which breaks the expected v sin i-color correlation. Future time-domain studies focusing on whether these slowly rotating stars are radial velocity variables are crucial to test the roles of stellar rotation and binarity in generating the split MSs.

astro-ph.SR↗

arXiv2019

No evidence for intermediate-mass black holes in the globular clusters $ω$ Cen and NGC 6624

We compare the results of a large grid of N-body simulations with the surface brightness and velocity dispersion profiles of the globular clusters $ω$ Cen and NGC 6624. Our models include clusters with varying stellar-mass black hole retention fractions and varying masses of a central intermediate-mass black hole (IMBH). We find that an $\sim 45,000$ M$_\odot$ IMBH, whose presence has been suggested based on the measured velocity dispersion profile of $ω$ Cen, predicts the existence of about 20 fast-moving, $m>0.5$ M$_\odot$ main-sequence stars with a (1D) velocity $v>60$ km/sec in the central 20 arcsec of $ω$ Cen. However no such star is present in the HST/ACS proper motion catalogue of Bellini et al. (2017), strongly ruling out the presence of a massive IMBH in the core of $ω$ Cen. Instead, we find that all available data can be fitted by a model that contains 4.6% of the mass of $ω$ Cen in a centrally concentrated cluster of stellar-mass black holes. We show that this mass fraction in stellar-mass BHs is compatible with the predictions of stellar evolution models of massive stars. We also compare our grid of $N$-body simulations with NGC 6624, a cluster recently claimed to harbor a 20,000 M$_\odot$ black hole based on timing observations of millisecond pulsars. However, we find that models with $M_{IMBH}>1,000$ M$_\odot$ IMBHs are incompatible with the observed velocity dispersion and surface brightness profile of NGC 6624,ruling out the presence of a massive IMBH in this cluster. Models without an IMBH provide again an excellent fit to NGC 6624.

astro-ph.GA↗