arXiv subjects

Fenghui Zhang

Publications and source records attributed to Fenghui Zhang.

At least 19 recordsLinked to original sources

arXiv2026

When Galaxies Refuel: Evolution of the Perturbed Spiral Galaxy NGC1385

The spiral galaxy NGC 1385 is characterized by a vigorous and protracted history of star formation, particularly in its central regions, leading to a current star formation rate that surpasses those of comparable systems. We analyze the evolution history of the galaxy using spatially resolved optical and submillimeter spectroscopy obtained from the PHANGS survey combined with WALLABY radio survey data. We construct radial distributions of star formation rate and the interstellar medium (ISM) neutral and molecular gas mass surface densities and measure the metallicity distribution of the stellar populations using a refined full-spectral fitting population synthesis method together with a determination of ISM oxygen abundances using H\,II region emission lines. The metallicities of the young stars and the ISM are similar and show an almost flat distribution. This is crucially different from previous work which had found a positive gradient for the average metallicities of the stars. We fit a chemical evolution model (incorporating gas infall, outflow, and radial inflow) to the observed data of NGC\,1385. Based on this fit, the evolution of NGC\,1385 is characterized by the typical inside-out disk formation of spiral galaxies -- even though our model does not assume an a priori shorter gas infall timescale for the inner disk than for the outer disk. However, the galaxy has experienced sustained star formation over gigayear timescales with a star formation efficiency a factor of two higher than normal. This explains the high metallicity of the young stars of 0.15 to 0.2\,dex higher than solar and the flat distribution of metallicity across the disk. The model predictions for the metallicities of the stars align well with the observed values, supporting the robustness of both our refined spectral fitting analysis and the inferred evolutionary scenario.

astro-ph.GA↗

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

Radial Profiles of Binary Fraction in Elliptical Galaxies

The radial profile of binary fraction may vary with environment and is of significant importance for studying the formation mechanisms of binary stars and their dynamical evolution within globular clusters (GCs) and galaxies. However, existing studies remain limited to the Milky Way and its neighboring galaxies. Leveraging the method proposed by Zhang et al. for estimating the variation of binary fraction from integrated spectral features, we analyze a sample of 513 elliptical galaxies drawn from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey to measure their radial binary fraction profiles. Our results show that after accounting for the effect induced by radial variations in the stellar population (SP), the median SP-subtracted binary fraction, $r_{\rm b,sub}^{\rm med}$, becomes approximately flat. For nearly all elliptical galaxies in our sample, the variation in binary fraction relative to the galaxy center at $1R_e$ is less than 5%. No clear correlation is found between the binary fraction gradient and the gradients of SP properties. Moreover, we also compare differences between ultraviolet (UV) upturn and non-UV upturn galaxies. The overall binary fraction profiles and SP properties of the non-UV upturn galaxies in our sample are comparable to those of the UV upturn galaxies. This similarity may arise from the presence of residual star formation (RSF) in the non-UV upturn systems.

astro-ph.GA↗

arXiv2026

Ragged Paged Attention: A High-Performance and Flexible LLM Inference Kernel for TPU

Large Language Model (LLM) deployment is increasingly shifting to cost-efficient accelerators like Google's Tensor Processing Units (TPUs), prioritizing both performance and total cost of ownership (TCO). However, existing LLM inference kernels and serving systems remain largely GPU-centric, and there is no well-established approach for efficiently mapping LLM workloads onto TPU architectures--particularly under the dynamic and ragged execution patterns common in modern serving. In this paper, we present Ragged Paged Attention (RPA), a high-performance and flexible attention kernel for TPUs, implemented using Pallas and Mosaic. RPA addresses these challenges through three key techniques: (1) fine-grained tiling to enable efficient dynamic slicing over ragged memory, (2) a custom software pipeline that fuses KV cache updates with attention computation, and (3) a distribution-aware compilation strategy that generates specialized kernels for decode, prefill, and mixed workloads. Evaluated on Llama 3 8B on TPU7x, RPA achieves up to 86% memory bandwidth utilization (MBU) in decode and 73% model FLOPs utilization (MFU) in prefill. Integrated as the primary TPU backend in vLLM and SGLang, RPA provides a production-grade foundation for efficient TPU inference and offers practical insights into kernel design.

cs.PF↗

arXiv2026

Towards Knowledgeable Deep Research: Framework and Benchmark

Deep Research (DR) requires LLM agents to autonomously perform multi-step information seeking, processing, and reasoning to generate comprehensive reports. In contrast to existing studies that mainly focus on unstructured web content, a more challenging DR task should additionally utilize structured knowledge to provide a solid data foundation, facilitate quantitative computation, and lead to in-depth analyses. In this paper, we refer to this novel task as Knowledgeable Deep Research (KDR), which requires DR agents to generate reports with both structured and unstructured knowledge. Furthermore, we propose the Hybrid Knowledge Analysis framework (HKA), a multi-agent architecture that reasons over both kinds of knowledge and integrates the texts, figures, and tables into coherent multimodal reports. The key design is the Structured Knowledge Analyzer, which utilizes both coding and vision-language models to produce figures, tables, and corresponding insights. To support systematic evaluation, we construct KDR-Bench, which covers 9 domains, includes 41 expert-level questions, and incorporates a large number of structured knowledge resources (e.g., 1,252 tables). We further annotate the main conclusions and key points for each question and propose three categories of evaluation metrics including general-purpose, knowledge-centric, and vision-enhanced ones. Experimental results demonstrate that HKA consistently outperforms most existing DR agents on general-purpose and knowledge-centric metrics, and even surpasses the Gemini DR agent on vision-enhanced metrics, highlighting its effectiveness in deep, structure-aware knowledge analysis. Finally, we hope this work can serve as a new foundation for structured knowledge analysis in DR agents and facilitate future multimodal DR studies.

cs.AI↗

arXiv2026

BayeSED-GALAXIES II. Bayesian full spectrum analysis of galaxies and application in the CSST wide-field slitless spectroscopy survey

The China Space Station Telescope (CSST) will conduct wide-field multiband photometric imaging and slitless spectroscopic surveys, advancing cosmology and galaxy evolution studies. Achieving CSST's cosmological goals requires precise redshifts ($\sigma_{\rm NMAD}\lesssim 0.002-0.005$) from low-resolution ($R\sim200$) and potentially blended slitless spectra. We present BayeSED3, extended for Bayesian full-spectrum analysis, including nebular emission modeling (via \textsc{Cloudy}) and a Bayesian treatment of the model scaling factor, improving reliability over optimization methods for low SNR spectra. Validated on realistic mock data generated with the CESS emulator (median SNR=1.65, including instrumental and self-blending effects), our method achieves excellent redshift precision with three-band (GU+GV+GI) spectroscopy: $\sigma_{\rm NMAD}=0.0008$ ($\sim$80% success) for star-forming and $\sigma_{\rm NMAD}=0.0015$ ($\sim$50% success) for quiescent galaxies. Stellar mass ($\sigma_{\rm NMAD}\approx0.015$ dex for SF, $\approx0.016$ dex for quiescent) and SFR ($\sigma_{\rm NMAD}\approx0.05$ dex for SF, especially at SNR>1) are reliably recovered. Self-blending increases scatter by $\gtrsim30%$, but combining spectroscopy with CSST's seven-band photometry significantly improves accuracy, especially for quiescent galaxies and data-limited cases. Single-band spectroscopy plus photometry yields reasonable redshifts: GU+photometry is limited, GI+photometry gives >60% (SF) and >40% (quiescent) success at $\sigma_{\rm NMAD}\lesssim0.002$, GV+photometry gives >35% (SF) and $\sim$40% (quiescent) at similar precision. The Bayesian framework offers a powerful method for accurate galaxy characterization, enhancing CSST's scientific outcomes despite the challenges of slitless spectroscopy.

astro-ph.GA↗

arXiv2025

Evolution and star formation history of NGC300 from a chemical evolution model with radial gas inflows

In the build-up of galactic discs gas infall is an important ingredient and it produces radial gas inflows as a physical consequence of angular momentum conservation, since the infalling gas on to the disc at a specific radius has lower angular momentum than the circular motions of the gas at the point of impact. NGC300 is a well studied isolated, bulge-less, and low-mass disc galaxy ideally suited for an investigation of galaxy evolution with radial gas inflows. To investigate the effects of radial gas inflows on the physical properties of NGC300, a chemical evolution model for NGC300 is constructed by assuming its disc builds up progressively by infalling of metall-free gas and outflowing of metal-enriched gas. Radial gas inflows are also considered in the model. Our model including the radial gas inflows and an inside-out disc formation scenario can simultaneously reproduce the present-day observed radial profiles of HI gas mass surface density, SFR surface density, sSFR, gas-phase and stellar metallicity. We find that, although the value of radial gas inflow velocity is as low as -0.1 km/s, the radial gas inflows steepen the present-day radial profiles of HI gas mass surface density, SFR surface density, and metallicity, but flatten the radial sSFR profile. Incorporating radial gas inflows significantly improves the agreement between our model predicted present-day sSFR profile and the observations of NGC300. It predicts a significant flattening of the metallicity gradient with cosmic time. We also find that the model predicted star formation has been more active recently, indicating that the radial gas inflows may be help to sustain star formation in local spirals, at least in NGC300.

astro-ph.GA↗

arXiv2025

KnowCoder-V2: Deep Knowledge Analysis

Deep knowledge analysis tasks always involve the systematic extraction and association of knowledge from large volumes of data, followed by logical reasoning to discover insights. However, to solve such complex tasks, existing deep research frameworks face three major challenges: 1) They lack systematic organization and management of knowledge; 2) They operate purely online, making it inefficient for tasks that rely on shared and large-scale knowledge; 3) They cannot perform complex knowledge computation, limiting their abilities to produce insightful analytical results. Motivated by these, in this paper, we propose a \textbf{K}nowledgeable \textbf{D}eep \textbf{R}esearch (\textbf{KDR}) framework that empowers deep research with deep knowledge analysis capability. Specifically, it introduces an independent knowledge organization phase to preprocess large-scale, domain-relevant data into systematic knowledge offline. Based on this knowledge, it extends deep research with an additional kind of reasoning steps that perform complex knowledge computation in an online manner. To enhance the abilities of LLMs to solve knowledge analysis tasks in the above framework, we further introduce \textbf{\KCII}, an LLM that bridges knowledge organization and reasoning via unified code generation. For knowledge organization, it generates instantiation code for predefined classes, transforming data into knowledge objects. For knowledge computation, it generates analysis code and executes on the above knowledge objects to obtain deep analysis results. Experimental results on more than thirty datasets across six knowledge analysis tasks demonstrate the effectiveness of \KCII. Moreover, when integrated into the KDR framework, \KCII can generate high-quality reports with insightful analytical results compared to the mainstream deep research framework.

cs.AI↗

arXiv2025

A post-common-envelope binary with double-peaked Balmer emission lines from TMTS

The dynamical method provides an efficient way to discover post-common-envelope binaries (PCEB) with faint white dwarfs (WDs), thanks to the development of time-domain survey projects. We perform a comprehensive analysis of the PCEB system TMTS J15530469+4457458 (J1553), discovered by the Tsinghua University-Ma Huateng Telescopes for Survey, to explore its physical origin and evolutionary fate. This system is characterized by double-peaked Balmer emission lines, and a cross-correlation function is applied to derive its radial velocity (RV) from a series of phase-resolved Keck spectra. Analyses with the cross-correlation function suggest that this system is a single-lined spectroscopic binary and only one star is optically visible. Further analysis through Doppler tomography indicates that J1553 is a detached binary without an accretion disk. Under such a configuration, the simultaneous light-curve and RV fitting reveal that this system contains an unseen WD with mass $M_{\rm A}=0.56\pm 0.09\, M_{\odot}$, and an M4 dwarf with mass $M_{\rm B}=0.37\pm 0.02\,M_{\odot}$ and radius $R_{\rm B}=0.403^{+0.014}_{-0.015}\,R_{\odot}$. The extra prominent Balmer emission lines seen in the spectra can trace the motion of the WD, which are likely formed near the WD surface as a result of wind accretion. According to the MESA simulation, J1553 could have evolved from a binary consisting of a 2.0-4.0 ${M}_{\odot}$ zero-age-main-sequence star and an M dwarf with an initial orbital period $P_i\approx 201-476$ d, and the system has undergone a common-envelope (CE) phase. After about $3.3\times10^6$ yr, J1553 should evolve into a cataclysmic variable, with a transient state as a supersoft X-ray source at the beginning. J1553 is an excellent system for studying wind accretion, CE ejection physics, and binary evolution theory.

astro-ph.SR↗

arXiv2025

Two categories of UV-upturn galaxies revealed by semi-analytic models

UV-upturn galaxies are characterized by unusually excessive flux in the far-ultraviolet (FUV) band, observed in some elliptical galaxies and the bulges of disk galaxies. We examine UV-upturn galaxies within the semi-analytic model GABE, which embeds the formation of extreme horizontal branch (EHB) stars -- proposed as key candidates responsible for the UV-upturn phenomenon. We have analyzed all related physical processes, including stellar evolution, initial mass functions (IMFs), dust attenuation, galaxy age, metallicity, and binary fractions, in an effort to determine which processes play significant roles. Our findings reveal two categories of UV-upturn galaxies in the semi-analytic model, each with distinct formation channels: old metal-rich quenched elliptical galaxies, which are intrinsic UV-upturn galaxies induced by EHB stars within their old stellar populations, and dusty star-forming galaxies, which are relatively young and may also be photometrically identified as UV-upturn galaxies when accounting for dust attenuation. Dust attenuation contributes to 20% - 60% of the UV-upturn galaxies, depending on the specific dust attenuation models adopted. With the binary star formation model of EHB stars, both of these formation channels exhibit strong preferences for high stellar metallicity. The high-mass end slope of the IMFs is found to have a marginal effect, indicating that a universal IMF is adequate for studying the UV-upturn phenomenon.

astro-ph.GA↗

arXiv2024

Short-period Post-Common Envelope Binaries with Balmer Emission from SDSS and LAMOST Based on ZTF Photometric Data

We present here 55 short period PCEBs containing a hot WD and a low-mass MS. Based on the photometric data from ZTF DR19, the light curves are analyzed for about 200 WDMS binaries with emission line(s) identified from SDSS or LAMOST spectra, in which 55 WDMS binaries are found to exhibit variability in their luminosities with a short period and are thus short-period binaries (i.e. PCEBs). In addition, it is found that the orbital periods of these PCEBs locate in a range from 2.2643 to 81.1526 hours. However, only 6 short-period PCEBs are newly discovered and the orbital periods of 19 PCEBs are improved in this work. Meanwhile, it is found that three objects are newly discovered eclipsing PCEBs, and a object (i.e. SDSS J1541) might be the short-period PCEB with a late M-type star or a brown dwarf companion based on the analysis of its spectral energy distribution. At last, the mechanism(s) being responsible for the emission features in the spectra of these PCEBs are discussed, the emission features arising in their optical spectra might be caused by the stellar activity or an irradiated component owing to a hot white dwarf companion because most of them contain a white dwarf with an effective temperature higher than $\sim$10,000 K.

astro-ph.SR↗

arXiv2023

The growth history of local M33-mass bulgeless spiral galaxies

NGC7793, NGC300, M33 and NGC2403 are four nearby undisturbed and bulgeless low-mass spiral galaxies with similar morphology and stellar mass. They are ideal laboratories to study disc formation scenarios and stellar mass growth histories. We construct a simple chemical evolution model by assuming that discs grow gradually with continuous metal-free gas infall and metal-enriched gas outflow. By means of the classical $χ^{2}$ methodology, applied to the model predictions, the best combination of free parameters capable of reproducing the corresponding present-day observations is determined, i.e. the radial dependence of the infall timescale $τ=0.1r/{R_{\rm d}}+3.4\,{\rm Gyr}$ ($R_{\rm d}$ is the disc scale-length) and the gas outflow efficiency $b_{\rm out}=0.2$. The model results are in excellent agreement with the general predictions of the inside-out growth scenario for the evolution of spiral galaxies. About 80\% of the stellar mass of NGC\,7793 is assembled within the last 8\,Gyr and 40\% within the last 4\,Gyr. By comparing the best-fitting model results of the three other galaxies we obtain similar results, 72\% (NGC300), 66\% (NGC2403) and 79\% (M33) stellar mass were assembled within the past $\sim\rm 8\,Gyr$ (i.e. $z\,=\,1$). These four disc galaxies simultaneously increase their sizes and stellar masses as time goes by and they grow in size at $\sim\,0.30$ times the rate at which they grow in mass. The scale-lengths of these four discs are now 20\% -- 25\% larger than at $z\,=\,1$. Our best-fitting model predicted the stellar mass-metallicity relation and the metallicity gradients, constrained by the observed metallicities from HII-regions emission line analysis, agree well with the observations measured from individual massive red and blue supergiant stars and population synthesis of SDSS galaxies.

astro-ph.GA↗

arXiv2021

Breaking the degeneracy between gas inflow and outflows with stellar metallicity: Insights on M101

An analytical chemical evolution model is constructed to investigate the radial distribution of gas-phase and stellar metallicity for star-forming galaxies. By means of the model, the gas-phase and stellar metallicity can be obtained from the stellar-to-gas mass ratio. Both the gas inflow and outflow processes play an important role in building the final gas-phase metallicity, and there exists degeneracy effect between the gas inflow and outflow rates for star-forming galaxies. On the other hand, stellar metallicity is more sensitive to the gas outflow rate than to the gas inflow rate, and this helps to break the parameter degeneracy for star-forming galaxies. We apply this analysis method to the nearby disc galaxy M\,101 and adopting the classical $χ^{2}$ methodology to explore the influence of model parameters on the resulted metallicity. It can be found that the combination of gas-phase and stellar metallicity is indeed more effective for constraining the gas inflow and outflow rates. Our results also show that the model with relatively strong gas outflows but weak gas inflow describes the evolution of M\,101 reasonably well.

astro-ph.GA↗

arXiv2020

Simulating Kilonovae in the ΛCDM Universe

Kilonovae are optical flashes produced in the aftermath of neutron star-neutron star mergers (NNMs) or neutron star-black hole mergers (NBMs). In this work, we use the Millennium Simulation, combined with a semi-analytic galaxy formation model--GABE (Galaxy Assembly with Binary Evolution) which adopts binary stellar population synthesis models, to explore the cosmic event rate of kilonovae, and the properties of their host galaxies in a cosmological context. We find that model with supernova kick velocity of 0 km/s fits the observation best, in agreement with the exception of some formation channels of binary neutron star. This indicates that NNMs prefer to originate from binary systems with low kick velocities. With V$_{\rm kick}$=0 km/s, the cosmic event rate of NNMs and NBMs at z=0 are 283 Gpc$^{-3}$yr$^{-1}$ and 91 Gpc$^{-3}$yr$^{-1}$, respectively, marginally consistent with the constraint from LVC GWTC-1. For Milky Way-mass galaxies, we predict the NNM rate is $25.7^{+59.6}_{-7.1}$ Myr$^{-1}$, which is also in good agreement with the observed properties of binary neutron stars in the Milky Way. Taking all the NNMs into account in the history of Milky Way-mass galaxies, we find that the averaged r-process elements yield with A>79 in a NNM and NBM event should be 0.01 M$_{\odot}$ to be consistent with observation. We conclude that NGC 4993, the host galaxy of GW170817, is a typical host galaxy for NNMs. However, generally NNMs and NBMs tend to reside in young, blue, star-forming, late-type galaxies, with stellar mass and gaseous metallicity distribution peaking at $10^{10.65}$ M$_{\odot}$ and 8.72-8.85, respectively. By studying kilonovae host galaxies in the cosmological background, it is promising to constrain model details better when we have more events in the forthcoming future. (abridged)

astro-ph.GA↗

arXiv2019

GABE: Galaxy Assembly with Binary Evolution

We developed a new semi-analytic galaxy formation model: Galaxy Assembly with Binary Evolution (GABE). For the first time we introduce binary evolution into semi-analytic models of galaxy formation by using Yunnan-II stellar population synthesis model, which includes various binary interactions. When implementing our galaxy formation model onto the merger trees extracted from the Millennium simulation, it can reproduce a large body of observational results. We find that in the local universe the model including binary evolution reduces the luminosity at optical and infrared wavelengths slightly, while increases the luminosity at ultraviolet wavelength significantly, especially in $F_{\rm UV}$ band. The resulting luminosity function does not change very much over SDSS optical bands and infrared band, but the predicted colors are bluer, especially when $F_{\rm UV}$ band is under consideration. The new model allows us to explore the physics of various high energy events related to the remnants of binary stars, e.g. type Ia supernovae, short gamma-ray bursts and gravitational wave events, and their relation with host galaxies in a cosmological context.

astro-ph.GA↗

arXiv2017

The role of environment on the star formation history of disc galaxies

NGC\,2403, NGC\,300 and M33 are three nearby pure-disc galaxies with similar stellar mass in different environments, they are benchmarks for understanding late-type spiral galaxies in different environments. The chemical evolution and growth of their discs are investigated by using the simple chemical evolution model, in which their discs are assumed to originate and grow through the accretion of the primordial gas, and the gas outflow process is also taken into account. Through comparative study of the best-fitting model predicted star formation histories for them, we hope to derive a picture of the local environment on the evolution and star formation histories of galaxies and whether or not the isolated galaxies follow similar evolution history. Our results show that these three galaxies accumulated more than 50 percent of their stellar mass at $z\,<\,1$. It can be also found that the metallicity gradients in isolated spiral galaxies NGC\,2403 and NGC\,300 are similar and obviously steeper than that in M33, when the metallicity gradients are expressed in ${\rm dex}\,R_{\rm 25}^{-1}$. The similar metallicity gradients in NGC\,2403 and NGC\,300 indicate that they may experience similar chemical evolutionary histories. The principal epoch of star formation on the discs of NGC\,2403 and NGC\,300 is earlier than that on the disc of M33, and the mean age of stellar populations along the discs of both NGC\,2403 and NGC\,300 is older than that of M33. Our results indicates that the evolution and star formation history of a galaxy indeed depends on its local environment, at least for galaxies with stellar mass of $10^{9.2}\,\rm M_{\odot}\sim10^{9.7}\,\rm M_{\odot}$.

astro-ph.GA↗

arXiv2015

The star-formation history of low-mass disk galaxies: a case study of NGC\,300

Since NGC300 is a bulge-less, isolated low-mass galaxy and has not experienced radial migration during its evolution history, it can be treated as an ideal laboratory to test simple galactic chemical evolution models. By assuming its disk forms gradually from continuous accretion of primordial gas and including the gas-outflow process, we construct a simple chemical evolution model for NGC300 to build a bridge between its SFH and its observed data, especially the present-day radial profiles and global observed properties (e.g., cold gas mass, star-formation rate and metallicity). By means of comparing the model predictions with the corresponding observations, we adopt the classical $χ^{2}$ methodology to find out the best combination of free parameters $a$, $b$ and $b_{\rm out}$. Our results show that, by assuming an inside-out formation scenario and an appropriate outflow rate, our model reproduces well most of the present-day observational values, not only the radial profiles but also the global observational data for the NGC300 disk. Our results suggest that NGC300 may experience a rapid growth of its disk. Through comparing the best-fitting model predicted SFH of NGC300 with that of M33, we find that the mean stellar age of NGC300 is older than that of M33 and there is a lack of primordial gas infall onto the disk of NGC300 recently. Our results also imply that the local environment may paly a key role in the secular evolution of NGC300.

astro-ph.GA↗

arXiv2015

A possible formation channel for blue hook stars in globular cluster

The formation mechanism for blue hook (BHk) stars in globular clusters (GCs) is still unclear. Following one of the possible scenario, named late hot flash scenario, we proposed that tidally enhanced stellar wind in binary evolution may provide the huge mass loss on the red giant branch (RGB) and produce BHk stars. Employing the detailed stellar evolution code, Modules for Experiments in Stellar Astrophysics (MESA), we investigated the contributions of tidally enhanced stellar wind as a possible formation channel for BHk stars in GCs. We evolved the primary stars with different initial orbital periods using the binary module in MESA (version 6208) from zero age main-sequence (ZAMS) to post horizontal branch (HB) stage, and obtained their evolution parameters which are compared with the observation. The results are consistent with observation in the color-magnitude diagram (CMD) and the logg-Teff plane for NGC 2808, which is an example GC hosting BHk stars. However, the helium abundance in the surface for our models is higher than the one obtained in BHk stars. This discrepancy between our models and observation is possibly due to the fact that gravitational settling and radiative levitation which are common processes in hot HB stars are not considered in the models as well as the fact that the flash mixing efficiency may be overestimated in the calculations. Our results suggested that tidally enhanced stellar wind in binary evolution is able to naturally provide the huge mass loss on the RGB needed for late hot flash scenario and it is a possible and reasonable formation channel for BHk stars in GCs.

astro-ph.SR↗