arXiv subjects

H. Jin

Publications and source records attributed to H. Jin.

At least 19 recordsLinked to original sources

arXiv2026

Multiplicity of Massive Stars at Low Metallicity: Early Results from the BLOeM Campaign

Massive stars at low metallicity (Z) play a central role in shaping the high-redshift Universe, yet their multiplicity remains poorly constrained. The Binarity at Low Metallicity (BLOeM) campaign is a two-year survey of 929 stars in the Small Magellanic Cloud with the Fibre Large Array Multi Element Spectrograph (FLAMES) instrument at ESO's Very Large Telescope, providing the first large-scale spectroscopic monitoring of massive stars at low Z (1/5 solar). Analysis of the initial nine epochs reveals high intrinsic binary fractions (>70%) on the main sequence and a steep decline in evolved objects. Analysis of the full dataset will yield orbital solutions, identify black-hole companions, and allow a derivation of the initial mass function for single and binary stars at low Z.

physics.gen-ph↗

arXiv2026

Multi-Dimensional MHD simulations of young Core-Collapse Supernova Remnants

Supernova remnants (SNRs) play a central role in shaping the interstellar medium. Core-Collapse Supernova (CCSN) progenitors are massive stars, which produce a dense circumstellar medium (CSM) through intense mass loss in post-main sequence evolution. The subsequent CCSN produces a strong shock which expands into a highly structured, complex magnetised environment. Magnetohydrodynamic (MHD) consideration of pre- and post-CCSN evolution in multi-D are desirable to further our understanding of non-thermal aspects. We aim to determine how detailed stellar evolution treatment influences the shock propagation, focusing on Red Supergiants (RSGs) and Wolf-Rayet (WR) stars. We use the PION code to perform 3D MHD simulations of these CCSN progenitors. We use a detailed stellar evolution prescription to accurately and self-consistently model the pre-SN CSM and initialise CCSN explosions to investigate the surrounding environment. Our 2D and 3D treatment, inclusion of radiative cooling and assumption of full photoionization produces CSM features not identified in previous work. In the WR model we produce a coherent set of fast reflected shocks. In both cases we find faster forward shocks than predicted by analytic theory due to additional wind acceleration from photoionization for the RSG case, and accounting for the CSM expansion in the WR case. Model predictions of slowly rotating RSG and WR stars results in weakly magnetised wind bubbles, limiting potential for their SNRs to become PeV particle accelerators. Detailed multi-D MHD treatment of the CSM is needed to account for SNR evolution beyond the wind termination shock, where dynamic instabilities can be important. Including self-consistent stellar evolution is important for determining the CSM density and magnetic field structure close to the star, which govern the shock properties and SNR evolution for the first few hundred yr. (Abridged)

astro-ph.SR↗

arXiv2026

EWOCS-V: Is Wd1-72 a recent post-interaction WR+O binary?

The evolutionary origin of Wolf-Rayet (WR) stars at Solar metallicity is unclear. Single-star evolution from massive O stars, possibly via a Luminous Blue Variable phase, is challenged by binary period distributions of different WR subtypes. Wd1-72 is a WN7b+O binary embedded in the collective wind of the Galactic young massive cluster Westerlund 1 (Wd 1). It is surrounded by highly structured nebulosity, with cometary tails pointing away from Wd 1 and quasi-spherical droplets towards it. In this letter, we demonstrate that this morphology can be qualitatively reproduced by a hydrodynamic simulation of non-conservative Roche Lobe Overflow (RLOF) mass-loss into a cluster wind. Our model is based on a detailed binary evolution track consistent with key known properties of Wd1-72. Our work suggests Wd1-72 could be only ~10 kyr post-RLOF, and the hydrogen-free nature of Wd1-72 favours this being a second or subsequent RLOF episode. Follow-up observations could make Wd1-72 a valuable benchmark for probing mass-loss and mass-transfer in forming gravitational-wave binary-progenitor systems.

astro-ph.SR↗

arXiv2026

The IACOB project: XVI. Surface helium abundances in Galactic O-type stars: indications for identifying binary interaction products

The presence of massive O-type stars with surfaces enriched by CNO-cycle products has been known since the early 1980s. For many years, internal rotational mixing was assumed to be the dominant mechanism responsible for this chemical contamination. However, accumulating evidence now suggests that binary interaction -- particularly mass-transfer episodes -- may play an equally important, if not dominant, role. We aim to carry out a large-scale investigation of surface helium (He) abundances in Galactic O-type stars, based on the results from the analysis of high-quality spectroscopic data from the IACOB project. We perform a homogeneous spectroscopic analysis of 318 Galactic O-type stars with the IACOB-BROAD and FASTWIND/IACOB-GBAT tools, deriving rotational velocities, atmospheric parameters, and He abundances. We also account for the influence of binarity, runaway status, and parameter degeneracies (e.g., microturbulence, wind properties, diagnostic lines, and companion contamination) on the abundance determinations. We present homogeneously determined surface He abundances (YHe=N(He)/N(H)) for the so far largest, statistically significant sample of Galactic O-type stars. About 78% of the stars show He abundances consistent with the previously proposed cosmic abundance standard of YHe=0.098$\pm$0.002. The remaining 22% display clear He enrichment (YHe>0.13). We also provide observational evidence indicating that most of these He-enriched stars are likely the products of binary interaction. Our study highlights how large spectroscopic surveys are gradually opening robust observational avenues to identify the products of massive binary interaction. It also emphasizes the need for caution when interpreting the spectroscopic properties of apparently single O-type stars. A significant fraction may in fact be the outcome of binary evolution rather than isolated stellar birth.

astro-ph.SR↗

arXiv2026

The drastic impact of Eddington-limit induced mass ejections on massive star populations

Massive stars are the key engines of the Universe. However, their evolution and thus their ionizing feedback are still not fully understood. One of the largest gaps in current stellar evolution calculations is the lack of a model for the mass ejections that occur when the stars reach the Eddington limit, such as during an Luminous Blue Variable (LBV) phase. We aim to remedy this situation by providing a physically motivated and empirically calibrated method applicable in any 1D stellar evolution code to approximate the effect of such mass loss on stellar evolution. We employ the 1D stellar evolution code MESA, in which we implement a new mass-loss prescription that is acting when stellar models inflate too much when reaching the Eddington limit. Synthetic massive-star stellar populations using calculated grids of single-star models with this mass loss prescription are compared with the observed populations in the Large and Small Magellanic Clouds. In combination with already computed grids of binary evolution models, we investigate the impact of binarity on our predictions. Our single-star models reproduce key features of the observed stellar populations, namely (i) the absence of stars located beyond the Humphreys-Davidson limit, (ii) an upper limit of RSG luminosities, (iii) the faintest observed single WR stars, (iv) the absolute number of O-stars, WRs, and RSGs, (v) WO stars in low metallicity environments, and (vi) the positions of LBV stars in the HRD. Our binary population explains at the same time the 70% binary fraction of O-stars and the 40% binary fraction of WR stars. However, our synthetic population also has caveats, such as an overproduction of bright H-free WN stars. Our results show that the effect of Eddington-limit induced mass ejections on the structure and evolution of massive stars can remove tension between predicted and observed massive star populations.

astro-ph.SR↗

arXiv2025

Binarity at LOw Metallicity (BLOeM): Projected rotational velocities

The Binarity at LOw Metallicity (BLOeM) survey is an ESO large programme designed to obtain multi-epoch spectroscopy for 929 massive stars in the Small Magellanic Cloud (SMC). It will provide binary fractions and orbital configurations of binary systems, and search for dormant black-hole binary candidates (OB+BH). Here we present projected rotational velocities (vsini) of all sources and, using the multiplicity properties presented in previous papers, we derive the vsini distributions of apparent single stars, single lined spectroscopic (SB1) binaries, and SB2 systems. We identify a locus in the Hertzsprung-Russell diagram where rotational velocities decrease significantly; we interpret this feature as broadly corresponding to the terminal-age main sequence. The main sequence cohort is distinguished by a broad range of vsini values, but with a strong peak in the distribution in the range 30-60 km/s, close to the resolution limit of 30 km/s. Sources in this low vsini peak are distributed throughout the main sequence, and are also present in the SB1 sample, though less prominent than in the single star distribution. A preliminary analysis of the lowest vsini cohort, that includes SB1 systems, implies that roughly one third may be nitrogen rich and we speculate that this cohort is a mix of pristine single stars, long period binaries, and merger products. The SB2 systems appear to be mostly short period binaries in synchronous rotation and have vsini estimates distributed around a mean value of approximately 140 km/s . Higher vsini sources are also present in the single and SB1 systems, all of which have tail to higher vsini values, consistent with tidal and mass-transfer effects. The supergiants, with a few exceptions, have low vsini, the bulk of these systems being essentially unresolved at current spectral resolution.

astro-ph.SR↗

arXiv2025

Populations of evolved massive binary stars in the Small Magellanic Cloud I: Predictions from detailed evolution models

Context. The majority of massive stars are born with a close binary companion. How this affects their evolution and fate is still largely uncertain, especially at low metallicity. Aims. We derive synthetic populations of massive post-interaction binary products and compare them with corresponding observed populations in the Small Magellanic Cloud (SMC). Methods. We analyse 53298 detailed binary evolutionary models computed with MESA. Our models include the physics of rotation, mass and angular momentum transfer, magnetic internal angular momentum transport, and tidal spin-orbit coupling. They cover initial primary masses of 5-100Msun, initial mass ratios of 0.3-0.95, and all initial periods for which interaction is expected. They are evolved through the first mass transfer and the donor star death, a possible ensuing Be/X-ray binary phase, and they end when the mass gainer leaves the main sequence. Results.In our fiducial synthetic population, 8% of the OB stars in the SMC are post-mass transfer systems, and 7% are merger products. In many of our models, the mass gainers are spun up and form Oe/Be stars. While our model underpredicts the number of Be/X-ray binaries in the SMC, it reproduces the main features of their orbital period distribution and the observed number of SMC binary WR stars. We expect $\sim$50 OB+BH binaries below and $\sim$170 above 20d orbital period. The latter might produce merging double BHs. However, their progenitors, the predicted long-period WR+OB binaries, are not observed. Conclusions. While the comparison with the observed SMC stars supports many physics assumptions in our high-mass binary models, a better match of the large number of observed OBe stars and Be/X-ray binaries likely requires a lower merger rate and/or a higher mass transfer efficiency during the first mass transfer. The fate of the initially wide O star binaries remains uncertain.

astro-ph.SR↗

arXiv2024

The IACOB project XIII. Helium enrichment in O-type stars as a tracer of past binary interaction

There is increasing evidence that single-star evolutionary models are inadequate to reproduce all observational properties of massive stars. Binary interaction has emerged as a key factor in the evolution of a significant fraction of massive stars. In this study, we investigate the helium ($Y_{\mathrm He}$) and nitrogen ($\epsilon_{\mathrm N}$) surface abundances in a comprehensive sample of 180 Galactic O-type stars with projected rotational velocities $v\sin(i)\leq150{\mathrm km}\cdot{\mathrm s}^{-1}$. We found a subsample ($\sim20\%$ of the total, and $\sim80\%$ of the stars with $Y_{\mathrm He}\geq0.12$) with a $Y_{\mathrm He}$ and $\epsilon_{\mathrm N}$ combined pattern unexplainable by single-star evolution. We argue that the stars with anomalous surface abundance patterns are binary interaction products.

astro-ph.SR↗

arXiv2024

Exploring the determinants on massive open online courses continuance learning intention in business toward accounting context

Massive open online courses (MOOC) have become important in the learning journey of college students and have been extensively implemented in higher education. However, there are few studies that investigated the willingness to continue using Massive open online courses (MOOC) in the field of business in higher education. Therefore, this paper proposes a comprehensive theoretical research framework based on the Theory of Planned Behavior (TPB). In the field of business, a representative accounting course is taken as an example. We adopt the questionnaire survey method and use the partial least squares structural equation model to analyze the collected feedback data from college students and test the hypotheses. This paper focuses on the potential influencing factors and mechanisms of the willingness to continuously use Massive open online courses (MOOC) in accounting. The results show that interface convenience (IC) and interface design aesthetics (IDA) have positive effects on user attitude (ATT). User attitude (ATT), perceived behavioral control (PBC), and subjective norms (SN) have positive effects on the continuance learning intention. In addition, academic self-efficacy (EF) not only significantly affects continuance learning intention (CI) but also moderates the relationship between the Theory of Planned Behavior (user attitude, perceived behavior control, subjective norms) and the continuance learning intention of accounting MOOC. Therefore, the Theory of Planned Behavior(TPB) is extended in social science accounting Massive open online courses environment. Based on these findings, this paper provides several theoretical and practical implications for researchers and practitioners of MOOC, accounting, and the design of learning systems in higher education contexts.

cs.CY↗

arXiv2024

Non-Fermi-liquid behavior in a ferromagnetic heavy fermion system CeTi$_{1-x}$V$_{x}$Ge$_{3}$

An investigation of the thermodynamic and electrical transport properties of the isoelectronic chemical substitution series CeTi$_{1-x}$V$_{x}$Ge$_{3}$ (CTVG) single crystals is reported. As x increases, the ferromagnetic (FM) transition temperature is suppressed, reaching absolute zero at the critical concentration x = 0.4, where a non-Fermi-liquid low-temperature specific heat and electrical resistivity, as well as the hyperscaling of specific heat and magnetization are found. Our study clearly identifies an FM quantum critical point (QCP) in CTVG. The obtained critical exponents suggest that CTVG falls in the preasymptotic region of the disorder-tuned FM QCP predicted by the Belitz-Kirkpatrick-Vojta theory.

cond-mat.str-el↗

arXiv2023

Variable Electrical Responses in Epitaxial Graphene Nanoribbons

We have demonstrated the fabrication of both armchair and zigzag epitaxial graphene nanoribbon (GNR) devices on 4H-SiC using a polymer-assisted sublimation growth method. The phenomenon of terrace step formation has traditionally introduced the risk of GNR deformation along sidewalls, but a polymer-assisted sublimation method helps mitigate this risk. Each type of 50 nm wide GNR is examined electrically and optically (armchair and zigzag), with the latter method being a check on the quality of the GNR devices and the former using alternating current to investigate resistance attenuation from frequencies above 100 Hz. Rates of attenuation are determined for each type of GNR device, revealing subtle suggested differences between armchair and zigzag GNRs.

cond-mat.mes-hall↗

arXiv2021

Improving spatial resolution of scanning SQUID microscopy with an on-chip design

Scanning superconducting quantum interference device microscopy (sSQUID) is currently one of the most effective methods for direct and sensitive magnetic flux imaging on the mesoscopic scale. A SQUID-on-chip design allows integration of field coils for susceptometry in a gradiometer setup which is very desirable for measuring magnetic responses of quantum matter. However, the spatial resolution of such a design has largely been limited to micrometers due to the difficulty in approaching the sample. Here, we used electron beam lithography technology in the fabrication of the 3D nano-bridge-based SQUID devices to prepare pick-up coils with diameters down to 150 nm. Furthermore, we integrated the deep silicon etching process in order to minimize the distance between the pick-up coil and the wafer edge. Combined with a tuning-fork-based scanning head, the sharpness of the etched chip edge enables a precision of 5 nm in height control. By scanning measurements on niobium chessboard samples using these improved SQUID devices, we demonstrate sub-micron spatial resolutions in both magnetometry and susceptometry, significantly better than our previous generations of nano-SQUIDs. Such improvement in spatial resolution of SQUID-on-chip is a valuable progress for magnetic imaging of quantum materials and devices in various modes.

cond-mat.mes-hall↗

arXiv2021

Near-Infrared and Optical Observations of Type Ic SN2020oi and broad-lined Ic SN2020bvc: Carbon Monoxide, Dust and High-Velocity Supernova Ejecta

We present near-infrared and optical observations of the Type Ic Supernova (SN) 2020oi in the galaxy M100 and the broad-lined Type Ic SN2020bvc in UGC 9379, using Gemini, LCO, SOAR, and other ground-based telescopes. The near-IR spectrum of SN2020oi at day 63 since the explosion shows strong CO emissions and a rising K-band continuum, which is the first unambiguous dust detection from a Type Ic SN. Non-LTE CO modeling shows that CO is still optically thick, and that the lower limit to the CO mass is 0.001 Msun. The dust temperature is 810 K, and the dust mass is ~10^(-5) Msun. We explore the possibilities that the dust is freshly formed in the ejecta, heated dust in the pre-existing circumstellar medium, and an infrared echo. The light curves of SN2020oi are consistent with a STELLA model with canonical explosion energy, 0.07 Msun Ni mass, and 0.7 Msun ejecta mass. A model of high explosion energy of ~10^(52) erg, 0.4 Msun Ni mass, 6.5 Msun ejecta mass with the circumstellar matter, reproduces the double-peaked light curves of SN2020bvc. We observe temporal changes of absorption features of the IR Ca~II triplet, S~I at 1.043 micron, and Fe~II at 5169 Angstrom. The blue-shifted lines indicate high velocities, up to 60,000 km/s for SN2020bvc and 20,000 km/s for SN2020oi, and the expansion velocity rapidly declines before the optical maximum. We present spectral signatures and diagnostics of CO and SiO molecular bands between 1.4 and 10 microns.

astro-ph.SR↗

arXiv2019

First assessment of the plant phenology index (PPI) for estimating gross primary productivity in African semi-arid ecosystems

The importance of semi-arid ecosystems in the global carbon cycle as sinks for CO2 emissions has recently been highlighted. Africa is a carbon sink and nearly half its area comprises arid and semi-arid ecosystems. However, there are uncertainties regarding CO2 fluxes for semi-arid ecosystems in Africa, particularly savannas and dry tropical woodlands. In order to improve on existing remote-sensing based methods for estimating carbon uptake across semi-arid Africa we applied and tested the recently developed plant phenology index (PPI). We developed a PPI-based model estimating gross primary productivity (GPP) that accounts for canopy water stress, and compared it against three other Earth observation-based GPP models: the temperature and greenness model, the greenness and radiation model and a light use efficiency model. The models were evaluated against in situ data from four semi-arid sites in Africa with varying tree canopy cover (3 to 65 percent). Evaluation results from the four GPP models showed reasonable agreement with in situ GPP measured from eddy covariance flux towers (EC GPP) based on coefficient of variation, root-mean-square error, and Bayesian information criterion. The PPI-based GPP model was able to capture the magnitude of EC GPP better than the other tested models. The results of this study show that a PPI-based GPP model is a promising tool for the estimation of GPP in the semi-arid ecosystems of Africa.

q-bio.PE↗

arXiv2018

Spincaloritronic measurements: a round robin comparison of the longitudinal spin Seebeck effect

The rising field of spin caloritronics focuses on the interactions between spin and heat currents in a magnetic material; the observation of the spin Seebeck effect opened the route to this branch of research. This paper reports the results of a round robin test performed by five partners on a single device highlighting the reproducibility problems related to the measurements of the spin Seebeck coefficient, the quantity that describes the strength of the spin Seebeck effect. This work stimulated the search for more reproducible measurement methods through the analysis of the systematic effects.

cond-mat.mes-hall↗

arXiv2015

Generating Searchable Public-Key Ciphertexts with Hidden Structures for Fast Keyword Search

Existing semantically secure public-key searchable encryption schemes take search time linear with the total number of the ciphertexts. This makes retrieval from large-scale databases prohibitive. To alleviate this problem, this paper proposes Searchable Public-Key Ciphertexts with Hidden Structures (SPCHS) for keyword search as fast as possible without sacrificing semantic security of the encrypted keywords. In SPCHS, all keyword-searchable ciphertexts are structured by hidden relations, and with the search trapdoor corresponding to a keyword, the minimum information of therelations is disclosed to a search algorithm as the guidance to find all matching ciphertexts efficiently. We construct a simple SPCHS scheme from scratch in which the ciphertexts have a hidden star-like structure. We prove our scheme to be semantically secure based on the decisional bilinear Diffie-Hellman assumption in the Random Oracle (RO) model. The search complexity of our scheme is dependent on the actual number of the ciphertexts containing the queried keyword, rather than the number of all ciphertexts. Finally, we present a generic SPCHS construction from anonymous identity-based encryption and collision-free full-identity malleable Identity-Based Key Encapsulation Mechanism (IBKEM) with anonymity. We illustrate two collision-free full-identity malleable IBKEM instances, which are semantically secure and anonymous, respectively, in the RO and standard models. The latter instance enables us to construct an SPCHS scheme with semantic security in the standard model.

cs.CR↗

arXiv2014

Reconfigurable on-chip entangled sources based on lithium-niobate waveguide circuits

Integrated quantum optics becomes a consequent tendency towards practical quantum information processing. Here, we report the on-chip generation and manipulation of photonic entanglement based on reconfigurable lithium niobate waveguide circuits. By introducing periodically poled structure into the waveguide interferometer, two individual photon-pair sources with controllable phase-shift are produced and cascaded by a quantum interference, resulting in a deterministically separated identical photon pair. The state is characterized by 92.9% visibility Hong-Ou-Mandel interference. Continuous morphing from two-photon separated state to bunched state is further demonstrated by on-chip control of electro-optic phase-shift. The photon flux reaches ~1.4*10^7 pairs nm-1 mW-1. Our work presents a scenario for on-chip engineering of different photon sources and paves a way to the fully integrated quantum technologies.

quant-ph↗

arXiv2013

Compact engineering of path-entangled sources from a monolithic quadratic nonlinear photonic crystal

Photonic entangled states lie at the heart of quantum science for the demonstrations of quantum mechanics foundations and supply as a key resource for approaching various quantum technologies. An integrated realization of such states will certainly guarantee a high-degree of entanglement and improve the performance like portability, stability and miniaturization, hence becomes an inevitable tendency towards the integrated quantum optics. Here, we report the compact realization of steerable photonic path-entangled states from a monolithic quadratic nonlinear photonic crystal. The crystal acts as an inherent beam splitter to distribute photons into coherent spatial modes, producing the heralded single-photon even appealing beamlike two-photon path-entanglement, wherein the entanglement is characterized by quantum spatial beatings. Such multifunctional entangled source can be further extended to high-dimensional fashion and multi-photon level as well as involved with other degrees of freedom, which paves a desirable way to engineer miniaturized quantum light source.

physics.optics↗