Showing 1–42 of 42 results for author: Li, E

The impact of AGN environmental effects on testing general relativity with space-borne gravitational wave detector

Authors: Xiangyu Lyu, Hongyu Chen, En-Kun Li, Yi-Ming Hu

Abstract: The space-borne gravitational wave detectors such as TianQin offers a new window to test General Relativity by observing the early inspiral phase of stellar-mass binary black holes. A key concern arises if these stellar-mass binary black holes reside in gaseous environments such as active galactic nucleus accretion disks, where environmental effects imprint detectable modulations on the gravitatio… ▽ More The space-borne gravitational wave detectors such as TianQin offers a new window to test General Relativity by observing the early inspiral phase of stellar-mass binary black holes. A key concern arises if these stellar-mass binary black holes reside in gaseous environments such as active galactic nucleus accretion disks, where environmental effects imprint detectable modulations on the gravitational waveform. Using Bayesian inference on simulated signals containing both environmental and dipole deviation, we have assessed the extent to which the presence of environmental effects affects the detectability of dipole radiation. Our results demonstrate that even in the presence of strong environmental coupling, the dipole parameter can be recovered with high precision, and the evidence for dipole radiation remains distinguishable. Crucially, we find that the existence of environmental effects does not fundamentally impede the identification of dipole radiation, provided both effects are simultaneously modelled in the inference process. This study establishes that future tests of modified gravity with space-borne observatories can remain robust even for sources in astrophysical environments. △ Less

Submitted 11 December, 2025; v1 submitted 10 December, 2025; originally announced December 2025.

Comments: We withdraw this manuscript because the results -- that AGN environmental effects do not hinder dipole-radiation searches -- remains preliminary. The methodology is sound, but the findings require further validation under broader astrophysical assumptions. To avoid potential misinterpretation, we decided to retract this version. We are retracting this version pending a more thorough investigation

Impact of Nuclear Reaction Rate Uncertainties on Type I X-ray Burst Nucleosynthesis: A Monte Carlo Study

Authors: Qing Wang, Ertao Li, Zhihong Li, Youbao Wang, Bing Guo, Yunju Li, Jun Su, Shipeng Hu, Yinwen Guan, Dong Xiang, Yu Liu, Lei Yang, Weiping Liu

Abstract: To investigate the impact of nuclear reaction rate uncertainties on type I X-ray burst nucleosynthesis, comprehensive Monte Carlo simulations are performed with temperature-independent and -dependent variations in reaction rates using the REACLIB and STARLIB libraries, respectively. A total of 1,711 $(p, γ)$, $(p, α)$, $(α, p)$, and $(α, γ)$ reactions are varied simultaneously, along with their in… ▽ More To investigate the impact of nuclear reaction rate uncertainties on type I X-ray burst nucleosynthesis, comprehensive Monte Carlo simulations are performed with temperature-independent and -dependent variations in reaction rates using the REACLIB and STARLIB libraries, respectively. A total of 1,711 $(p, γ)$, $(p, α)$, $(α, p)$, and $(α, γ)$ reactions are varied simultaneously, along with their inverse reactions, via detailed balance. For the first time, it is found that Monte Carlo sampling with larger perturbations to these reaction rates may lead to multi-peaked abundance distributions for some isotopes. These multi-peak structures arise not only from coupled reactions but also, in some cases, from single reactions. Our study also confirmed previously identified key reactions and provides more robust lists. These reactions deserve priority consideration in future study. △ Less

Submitted 1 December, 2025; originally announced December 2025.

Comments: 23 pages, 13 figures, 2 tables

Probing AGN Disks Density Profiles through Gravitational Wave Observations

Authors: Xiangyu Lyu, En-Kun Li, Changfu Shi, Yi-Ming Hu

Abstract: Massive black holes surrounded by a gaseous disk have been a prevailing model to explain a wide spectrum of astrophysical phenomena related to active galactic nucle (AGNs). However, direct and precise measurements of the disk density profiles remain elusive for current telescopes. In this work, we demonstrate that it is possible to pinpoint the gas density if an inspiralling stellar mass binary bl… ▽ More Massive black holes surrounded by a gaseous disk have been a prevailing model to explain a wide spectrum of astrophysical phenomena related to active galactic nucle (AGNs). However, direct and precise measurements of the disk density profiles remain elusive for current telescopes. In this work, we demonstrate that it is possible to pinpoint the gas density if an inspiralling stellar mass binary black hole is embedded in the AGN disk. Furthermore, if the barycenter of the pair follows an eccentric orbit around an AGN, then space-borne gravitational wave detectors can measure the density of the surrounding disk with multi-year observations by tracking the gravitational wave evolution. The error between the inferred density profile and the injected truth can be constrained to below $2\times10^{-11}\rm g/cm^3$. Our work opens up an exciting new channel to investigate the very center of galaxies, where disk gas density distributions $ρ(r)$ can be recovered by analyzing time-dependent environmental imprints in gravitational waveforms. △ Less

Submitted 13 November, 2025; originally announced November 2025.

Spinning into the Gap: Direct-Horizon Collapse as the Origin of GW231123 from End-to-End GRMHD Simulations

Authors: Ore Gottlieb, Brian D. Metzger, Danat Issa, Sean E. Li, Mathieu Renzo, Maximiliano Isi

Abstract: GW231123, the most massive binary black hole (BH) merger observed to date, involves component BHs with masses inside the pair-instability mass gap and unusually high spins. This challenges standard formation channels such as classical stellar evolution and hierarchical mergers. However, stellar rotation and magnetic fields, which have not been systematically incorporated in prior models, can stron… ▽ More GW231123, the most massive binary black hole (BH) merger observed to date, involves component BHs with masses inside the pair-instability mass gap and unusually high spins. This challenges standard formation channels such as classical stellar evolution and hierarchical mergers. However, stellar rotation and magnetic fields, which have not been systematically incorporated in prior models, can strongly influence the BH properties. We present the first self-consistent simulations tracking a massive, low-metallicity helium star from helium core burning through collapse, BH formation, and post-BH formation accretion using 3D general-relativistic magnetohydrodynamic (GRMHD) simulations. Starting from a $250\,M_\odot$ helium core, we show that collapse above the pair-instability mass gap, aided by rotation and magnetic fields, drives mass loss through disk winds and jet launching. This enables the formation of highly spinning BHs within the mass gap and reveals a BH spin-mass correlation. Strong magnetic fields extract angular momentum from the BH through magnetically driven outflows, which in turn suppress accretion, resulting in slowly spinning BHs within the mass gap. In contrast, stars with weak fields permit nearly complete collapse and spin-up of the BH to $ a\approx1$. We show that massive low-metallicity stars with moderate magnetic fields naturally produce BHs whose masses and spins match those inferred for GW231123, and are also consistent with those of GW190521. The outflows may impart a BH kick, which can induce spin-orbit misalignment and widen the post-collapse orbit, delaying the merger. The outflows launched during collapse may power short-lived, high-luminosity jets comparable to the most energetic $γ$-ray bursts, offering a potential observational signature of such events in the early universe. △ Less

Submitted 27 September, 2025; v1 submitted 21 August, 2025; originally announced August 2025.

Exploring the Link between Fast Radio Burst and Binary Neutron Star Origins with Spaceborne Gravitational Wave Observations

Authors: Yu-xuan Yin, En-kun Li, Bing Zhang, Yi-Ming Hu

Abstract: The origin of repeating Fast Radio Bursts (FRBs) is an open question, with observations suggesting that at least some are associated with old stellar populations. It has been proposed that some repeating FRBs may be produced by interactions of the binary neutron star magnetospheres decades to centuries before the coalescence. These systems would also emit centi-Hertz gravitational waves during thi… ▽ More The origin of repeating Fast Radio Bursts (FRBs) is an open question, with observations suggesting that at least some are associated with old stellar populations. It has been proposed that some repeating FRBs may be produced by interactions of the binary neutron star magnetospheres decades to centuries before the coalescence. These systems would also emit centi-Hertz gravitational waves during this period, which can be detectable by space-borne gravitational wave detectors. We explore the prospects of using current and future space-borne gravitational wave detectors, such as TianQin, LISA, and DECIGO, to test this FRB formation hypothesis. Focusing on nearby galaxies like M81, which hosts a repeating FRB source in a globular cluster, we calculate the detection capabilities for binary neutron star systems. Our analysis reveals that while missions like TianQin and LISA face limitations in horizon distance, changing detector pointing direction could significantly enhance detection probabilities. Considering the chance of a Milky Way-like galaxy coincidentally containing a BNS within 100 years before merger is only $3\times10^{-5}$ to $5\times10^{-3}$, if a signal is detected originating from M81, we can establish the link between FRB and binary neutron stars with a significance level of at least 2.81$σ$, or a Bayes factor of $4\times10^6 - 7\times10^8$ / $5\times10^2 - 10^5$ against the background model with optimistic/realistic assumptions. Next-generation detectors such as DECIGO offer enhanced capabilities and should easily detect these systems in M81 and beyond. Our work highlights the critical role of space-borne gravitational wave missions in unraveling FRB origins. △ Less

Submitted 17 June, 2025; v1 submitted 14 June, 2025; originally announced June 2025.

Comments: The Astrophysical Journal Letters, Volume 985, Number 2

Evaluating statistical significance for massive black hole binary mergers with space-based gravitational wave detectors

Authors: Hong-Yu Chen, En-Kun Li, Yi-Ming Hu

Abstract: Important scientific discoveries should be backed by high statistical significance. In the 2030s, multiple space-based gravitational wave detectors are expected to operate. While many works aim to achieve quick and reliable detection and parameter estimation of millihertz gravitational wave sources, dedicated studies are lacking to assess the significance of space-based detectors. In this work, we… ▽ More Important scientific discoveries should be backed by high statistical significance. In the 2030s, multiple space-based gravitational wave detectors are expected to operate. While many works aim to achieve quick and reliable detection and parameter estimation of millihertz gravitational wave sources, dedicated studies are lacking to assess the significance of space-based detectors. In this work, we propose a framework to assess the statistical significance of massive black hole binaries (MBHBs) detections with space-based gravitational wave detectors. We apply this algorithm to simulated data with Gaussian stationary noise and the complex LDC-2a dataset to measure the false alarm rate and significance of MBHB signals. We also analyze factors affecting the significance of MBHBs and design a method to mitigate multi-source confusion interference. In Gaussian noise conditions, MBHBs with a signal-to-noise ratio of about 7 can achieve $3 σ$ significance, and those with a signal-to-noise ratio of about 8 achieve $4 σ$. Our analysis demonstrates that all MBHB signals in the LDC-2a dataset have a significance exceeding $4.62 σ$. △ Less

Submitted 14 May, 2025; originally announced May 2025.

Comments: 8 pages, 6 figures, comments welcome

Adaptive Modeling of Correlated Noise in Space-Based Gravitational Wave Detectors

Authors: Ya-Nan Li, Yi-Ming Hu, En-Kun Li

Abstract: Accurately estimating the statistical properties of noise is important in data analysis for space-based gravitational wave detectors. Noise in different time-delay interferometry channels correlates with each other. Many studies often assume uncorrelated noise and ignore the off-diagonal elements in the noise covariance matrix. This could lead to some bias in the parameter estimation of gravitatio… ▽ More Accurately estimating the statistical properties of noise is important in data analysis for space-based gravitational wave detectors. Noise in different time-delay interferometry channels correlates with each other. Many studies often assume uncorrelated noise and ignore the off-diagonal elements in the noise covariance matrix. This could lead to some bias in the parameter estimation of gravitational wave signals. In this paper, we present a framework for reconstructing the full noise covariance matrix, including frequency-dependent auto- and cross-correlated power spectral densities, without assuming the parametric analytic expressions of the noise model. Our approach combines spline interpolation with trigonometric basis functions to construct a semi-analytical representation of the noise. We then employ trans-dimensional Bayesian inference to fit the correlated noise structure.The resulting software package, $\texttt{NOISAR}$, successfully recovers both auto- and cross-correlated power spectral features with a relative error of about $10\%$. △ Less

Submitted 17 June, 2025; v1 submitted 17 April, 2025; originally announced April 2025.

Comments: 20 pages, 6 figures. Accepted for publication in CQG

Fundamental Physics and Cosmology with TianQin

Authors: Jun Luo, Haipeng An, Ligong Bian, Rong-Gen Cai, Zhoujian Cao, Wenbiao Han, Jianhua He, Martin A. Hendry, Bin Hu, Yi-Ming Hu, Fa Peng Huang, Shun-Jia Huang, Sang Pyo Kim, En-Kun Li, Yu-Xiao Liu, Vadim Milyukov, Shi Pi, Konstantin Postnov, Misao Sasaki, Cheng-Gang Shao, Lijing Shao, Changfu Shi, Shuo Sun, Anzhong Wang, Pan-Pan Wang , et al. (10 additional authors not shown)

Abstract: The exploration of the surrounding world and the universe is an important theme in the legacy of humankind. The detection of gravitational waves is adding a new dimension to this grand effort. What are the fundamental physical laws governing the dynamics of the universe? What is the fundamental composition of the universe? How has the universe evolved in the past and how will it evolve in the futu… ▽ More The exploration of the surrounding world and the universe is an important theme in the legacy of humankind. The detection of gravitational waves is adding a new dimension to this grand effort. What are the fundamental physical laws governing the dynamics of the universe? What is the fundamental composition of the universe? How has the universe evolved in the past and how will it evolve in the future? These are the basic questions that press for answers. The space-based gravitational wave detector TianQin will tune in to gravitational waves in the millihertz frequency range ($10^{-4} \sim 1$ Hz, to be specific), opening a new gravitational wave spectrum window to explore many of the previously hidden sectors of the universe. TianQin will discover many astrophysical systems, populating the universe at different redshifts: some will be of new types that have never been detected before, some will have very high signal-to-noise ratios, and some will have very high parameter estimation precision. The plethora of information collected will bring us to new fronts on which to search for the breaking points of general relativity, the possible violation of established physical laws, the signature of possible new gravitational physics and new fundamental fields, and to improve our knowledge on the expansion history of the universe. In this white paper, we highlight the advances that TianQin can bring to fundamental physics and cosmology. △ Less

Submitted 27 February, 2025; originally announced February 2025.

Comments: 113 pages

Progress of the TianQin project

Authors: Jun Luo, Shaojun Bai, Yan-Zheng Bai, Lin Cai, Hao Dang, Qijia Dong, Hui-Zong Duan, Yuanbo Du, Lei Fan, Xinju Fu, Yong Gao, Xingyu Gou, Changlei Guo, Wei Hong, Bin Hu, Heran Hu, Ming Hu, Yi-Ming Hu, Fa Peng Huang, Defeng Gu, Xin Ji, Yuan-Ze Jiang, En-Kun Li, Hongyin Li, Ming Li , et al. (76 additional authors not shown)

Abstract: TianQin is a future space-based gravitational wave observatory targeting the frequency window of $10^{-4}$ Hz $\sim 1$ Hz. A large variety of gravitational wave sources are expected in this frequency band, including the merger of massive black hole binaries, the inspiral of extreme/intermediate mass ratio systems, stellar-mass black hole binaries, Galactic compact binaries, and so on. TianQin will… ▽ More TianQin is a future space-based gravitational wave observatory targeting the frequency window of $10^{-4}$ Hz $\sim 1$ Hz. A large variety of gravitational wave sources are expected in this frequency band, including the merger of massive black hole binaries, the inspiral of extreme/intermediate mass ratio systems, stellar-mass black hole binaries, Galactic compact binaries, and so on. TianQin will consist of three Earth orbiting satellites on nearly identical orbits with orbital radii of about $10^5$ km. The satellites will form a normal triangle constellation whose plane is nearly perpendicular to the ecliptic plane. The TianQin project has been progressing smoothly following the ``0123" technology roadmap. In step ``0", the TianQin laser ranging station has been constructed and it has successfully ranged to all the five retro-reflectors on the Moon. In step ``1", the drag-free control technology has been tested and demonstrated using the TianQin-1 satellite. In step ``2", the inter-satellite laser interferometry technology will be tested using the pair of TianQin-2 satellites. The TianQin-2 mission has been officially approved and the satellites will be launched around 2026. In step ``3", i.e., the TianQin-3 mission, three identical satellites will be launched around 2035 to form the space-based gravitational wave detector, TianQin, and to start gravitational wave detection in space. △ Less

Submitted 16 February, 2025; originally announced February 2025.

Comments: 45 pages, 3 figures

Detection of the stochastic gravitational wave background with the space-borne gravitational-wave detector network

Authors: Jun Cheng, En-Kun Li, Jianwei Mei

Abstract: The stochastic gravitational wave background (SGWB) is one of the main detection targets for future millihertz space-borne gravitational-wave observatories such as the \ac{LISA}, TianQin, and Taiji. For a single LISA-like detector, a null-channel method was developed to identify the SGWB by integrating data from the A and E channels with a noise-only T channel. However, the noise monitoring channe… ▽ More The stochastic gravitational wave background (SGWB) is one of the main detection targets for future millihertz space-borne gravitational-wave observatories such as the \ac{LISA}, TianQin, and Taiji. For a single LISA-like detector, a null-channel method was developed to identify the SGWB by integrating data from the A and E channels with a noise-only T channel. However, the noise monitoring channel will not be available if one of the laser interferometer arms fails. By combining these detectors, it will be possible to build detector networks to search for SGWB via cross-correlation analysis.In this work, we developed a Bayesian data analysis method based on \ac{TDI} Michelson-type channel. We then investigate the detectability of the TianQin-LISA detector network for various isotropic SGWB. Assuming a three-month observation, the TianQin-LISA detector network could be able to confidently detect SGWB with energy density as low as $Ω_{\rm PL} = 6.0 \times 10^{-13}$, $Ω_{\rm Flat} = 2.0 \times 10^{-12}$ and $Ω_{\rm SP} = 1.2 \times 10^{-12}$ for power-law, flat and single-peak models, respectively. △ Less

Submitted 6 November, 2025; v1 submitted 24 January, 2025; originally announced January 2025.

Signal-to-noise Ratio Analytic Formulae of the Inspiral Binary Black Holes in TianQin

Authors: Hong-Yu Chen, Han Wang, En-Kun Li, Yi-Ming Hu

Abstract: Binary black holes are one of the important sources for the TianQin gravitational wave project. Our research has revealed that, for TianQin, the signal-to-noise ratio of inspiral binary black holes can be computed analytically. This finding is expected to greatly simplify the estimation of detection capabilities for binary black holes. In this paper, we demonstrated the signal-to-noise ratio relat… ▽ More Binary black holes are one of the important sources for the TianQin gravitational wave project. Our research has revealed that, for TianQin, the signal-to-noise ratio of inspiral binary black holes can be computed analytically. This finding is expected to greatly simplify the estimation of detection capabilities for binary black holes. In this paper, we demonstrated the signal-to-noise ratio relationships from stellar-mass black holes to massive black holes. With the all-sky average condition, the signal-to-noise ratio for most binary black hole signals can be determined with a relative error of $\lesssim10\%$, with notable deviations only for chirp masses near $1000~M_\odot$. In contrast, the signal-to-noise ratio without the average includes an additional term, which we refer to as the response factor. Although this term is not easily calculated analytically, we provide a straightforward estimation method with an error margin of $1σ$ within 2\%. △ Less

Submitted 7 July, 2025; v1 submitted 25 October, 2024; originally announced October 2024.

Comments: 16 pages, 6 figures, comments welcome

Journal ref: Class. Quantum Grav. 42 155010 (2025)

Gravitational Wave Astronomy With TianQin

Authors: En-Kun Li, Shuai Liu, Alejandro Torres-Orjuela, Xian Chen, Kohei Inayoshi, Long Wang, Yi-Ming Hu, Pau Amaro-Seoane, Abbas Askar, Cosimo Bambi, Pedro R. Capelo, Hong-Yu Chen, Alvin J. K. Chua, Enrique Condés-Breña, Lixin Dai, Debtroy Das, Andrea Derdzinski, Hui-Min Fan, Michiko Fujii, Jie Gao, Mudit Garg, Hongwei Ge, Mirek Giersz, Shun-Jia Huang, Arkadiusz Hypki , et al. (28 additional authors not shown)

Abstract: The opening of the gravitational wave window has significantly enhanced our capacity to explore the universe's most extreme and dynamic sector. In the mHz frequency range, a diverse range of compact objects, from the most massive black holes at the farthest reaches of the Universe to the lightest white dwarfs in our cosmic backyard, generate a complex and dynamic symphony of gravitational wave sig… ▽ More The opening of the gravitational wave window has significantly enhanced our capacity to explore the universe's most extreme and dynamic sector. In the mHz frequency range, a diverse range of compact objects, from the most massive black holes at the farthest reaches of the Universe to the lightest white dwarfs in our cosmic backyard, generate a complex and dynamic symphony of gravitational wave signals. Once recorded by gravitational wave detectors, these unique fingerprints have the potential to decipher the birth and growth of cosmic structures over a wide range of scales, from stellar binaries and stellar clusters to galaxies and large-scale structures. The TianQin space-borne gravitational wave mission is scheduled for launch in the 2030s, with an operational lifespan of five years. It will facilitate pivotal insights into the history of our universe. This document presents a concise overview of the detectable sources of TianQin, outlining their characteristics, the challenges they present, and the expected impact of the TianQin observatory on our understanding of them. △ Less

Submitted 2 December, 2024; v1 submitted 29 September, 2024; originally announced September 2024.

Comments: TianQin Gravitational Wave Whitepaper, 72 pages, 30 figures

Mapping Anisotropies in the Stochastic Gravitational-Wave Background with TianQin

Authors: Zhi-Yuan Li, Zheng-Cheng Liang, En-Kun Li, Jian-dong Zhang, Yi-Ming Hu

Abstract: In the milli-Hertz frequency band, stochastic gravitational-wave background can be composed of both astronomical and cosmological sources, both can be anisotropic. Numerically depicting these anisotropies can be critical in revealing the underlying properties of their origins. For the first time, we perform a theoretical analysis of the constraining ability of TianQin on multiple moments of the st… ▽ More In the milli-Hertz frequency band, stochastic gravitational-wave background can be composed of both astronomical and cosmological sources, both can be anisotropic. Numerically depicting these anisotropies can be critical in revealing the underlying properties of their origins. For the first time, we perform a theoretical analysis of the constraining ability of TianQin on multiple moments of the stochastic background. First, we find that with a one-year operation, for a background with a signal-to-noise ratio of 16, TianQin can recover the multiple moments up to $l=4$. We also identified a unique feature of the stochastic background sky map, which is the mirror symmetry along the fixed orbital plane of TianQin. Thirdly, we explain the difference in anisotropy recovering ability between TianQin and LISA, by employing the criteria of the singularity of the covariance matrix (which is the condition number). Finally, we find that since the different data channel combinations correspond to different singularities, certain combinations might have an advantage in stochastic background map-making. We believe that the findings of this work can provide an important reference to future stochastic background analysis pipelines. It can also serve as a guideline for designing better gravitational-wave detectors aiming to decipher anisotropies in the stochastic background. △ Less

Submitted 17 September, 2024; originally announced September 2024.

Comments: 12 pages, 6 figures

Dealing with data gaps for TianQin with massive black hole binary signal

Authors: Lu Wang, Hong-Yu Chen, Xiangyu Lyu, En-Kun Li, Yi-Ming Hu

Abstract: Space-borne gravitational wave detectors like TianQin might encounter data gaps due to factors like micrometeoroid collisions or hardware failures. Such events will cause discontinuity in the data, presenting challenges to the data analysis for TianQin, especially for massive black hole binary mergers. Since the signal-to-noise ratio (SNR) accumulates in a non-linear way, a gap near the merger cou… ▽ More Space-borne gravitational wave detectors like TianQin might encounter data gaps due to factors like micrometeoroid collisions or hardware failures. Such events will cause discontinuity in the data, presenting challenges to the data analysis for TianQin, especially for massive black hole binary mergers. Since the signal-to-noise ratio (SNR) accumulates in a non-linear way, a gap near the merger could lead to a significant loss of SNR. It could introduce bias in the estimate of noise properties, and the results of the parameter estimation. In this work, using simulated TianQin data with injected a massive black hole binary merger, we study the window function method, and for the first time, the inpainting method to cope with the data gap, and an iterative estimate scheme is designed to properly estimate the noise spectrum. We find that both methods can properly estimate noise and signal parameters. The easy-to-implement window function method can already perform well, except that it will sacrifice some SNR due to the adoption of the window. The inpainting method is slower, but it can minimize the impact of the data gap. △ Less

Submitted 1 February, 2025; v1 submitted 23 May, 2024; originally announced May 2024.

Comments: 17 pages, 9 figures, comments welcome

An Opacity-Free Method of Testing the Cosmic Distance Duality Relation Using Strongly Lensed Gravitational Wave Signals

Authors: Shun-Jia Huang, En-Kun Li, Jian-dong Zhang, Xian Chen, Zucheng Gao, Xin-yi Lin, Yi-Ming Hu

Abstract: The cosmic distance duality relation (CDDR), expressed as DL(z) = (1 + z)2DA(z), plays an important role in modern cosmology. In this paper, we propose a new method of testing CDDR using strongly lensed gravitational wave (SLGW) signals. Under the geometric optics approximation, we calculate the gravitational lens effects of two lens models, the point mass and singular isothermal sphere. We use fu… ▽ More The cosmic distance duality relation (CDDR), expressed as DL(z) = (1 + z)2DA(z), plays an important role in modern cosmology. In this paper, we propose a new method of testing CDDR using strongly lensed gravitational wave (SLGW) signals. Under the geometric optics approximation, we calculate the gravitational lens effects of two lens models, the point mass and singular isothermal sphere. We use functions of η1(z) = 1 + η0z and η2(z) = 1 + η0z=(1 + z) to parameterize the deviation of CDDR. By reparameterizing the SLGW waveform with CDDR and the distance-redshift relation, we include the deviation parameters η0 of CDDR as waveform parameters. We evaluate the ability of this method by calculating the parameter estimation of simulated SLGW signals from massive binary black holes. We apply the Fisher information matrix and Markov Chain Monte Carlo methods to calculate parameter estimation. We find that with only one SLGW signal, the measurement precision of η0 can reach a considerable level of 0.5-1.3% for η1(z) and 1.1-2.6% for η2(z), depending on the lens model and parameters. △ Less

Submitted 27 February, 2024; originally announced February 2024.

Comments: 15 pages, 7 figures

Bayesian parameter estimation of massive black hole binaries with TianQin-LISA

Authors: Jie Gao, Yi-Ming Hu, En-Kun Li, Jian-dong Zhang, Jianwei Mei

Abstract: This paper analyses the impact of various parameter changes on the estimation of parameters for massive black hole binary (MBHB) systems using a Bayesian inference technique. Several designed MBHB systems were chosen for comparison with a fiducial system to explore the influence of parameters such as sky location, inclination angle, anti-spin, large mass ratio and light mass. And the two reported… ▽ More This paper analyses the impact of various parameter changes on the estimation of parameters for massive black hole binary (MBHB) systems using a Bayesian inference technique. Several designed MBHB systems were chosen for comparison with a fiducial system to explore the influence of parameters such as sky location, inclination angle, anti-spin, large mass ratio and light mass. And the two reported MBHB candidates named OJ287 and Tick-Tock are also considered. The study found that the network of TianQin and LISA can break certain degeneracies among different parameters, improving the estimation of parameters, particularly for extrinsic parameters. Meanwhile, the degeneracies between different intrinsic parameters are highly sensitive to the value of the parameters. Additionally, the small inclination angles and limited detection of the inspiral phase can introduce significant bias in the estimation of parameters. The presence of instrument noise will also introduce bias and worsen the precision. The paper concludes that the network of TianQin and LISA can significantly improve the estimation of extrinsic parameters by about one order of magnitude while yielding slight improvements in the intrinsic parameters. Moreover, parameter estimation can still be subject to biases even with a sufficiently high signal-to-noise ratio if the detected signal does not encompass all stages of the inspiral, merger, and ringdown. △ Less

Submitted 23 January, 2024; originally announced January 2024.

Comments: 17 pages, 10 figures

GWSpace: a multi-mission science data simulator for space-based gravitational wave detection

Authors: En-Kun Li, Han Wang, Hong-Yu Chen, Huimin Fan, Ya-Nan Li, Zhi-Yuan Li, Zheng-Cheng Liang, Xiang-Yu Lyu, Tian-Xiao Wang, Zheng Wu, Chang-Qing Ye, Xue-Ting Zhang, Yiming Hu, Jianwei Mei

Abstract: Space-based gravitational wave detectors such as TianQin, LISA, and TaiJi have the potential to outperform themselves through joint observation. To achieve this, it is desirable to practice joint data analysis in advance on simulated data that encodes the intrinsic correlation among the signals found in different detectors that operate simultaneously. In this paper, we introduce GWSpace, a package… ▽ More Space-based gravitational wave detectors such as TianQin, LISA, and TaiJi have the potential to outperform themselves through joint observation. To achieve this, it is desirable to practice joint data analysis in advance on simulated data that encodes the intrinsic correlation among the signals found in different detectors that operate simultaneously. In this paper, we introduce GWSpace, a package that can simulate the joint detection data from TianQin, LISA, and TaiJi. The software is not a groundbreaking work that starts from scratch. Rather, we use as many open-source resources as possible, tailoring them to the needs of simulating the multi-mission science data and putting everything into a ready-to-go and easy-to-use package. We shall describe the main components, the construction, and a few examples of application of the package. A common coordinate system, namely the Solar System Barycenter (SSB) coordinate system, is utilized to calculate spacecraft orbits for all three missions. The paper also provides a brief derivation of the detection process and outlines the general waveform of sources detectable by these detectors. △ Less

Submitted 28 August, 2025; v1 submitted 26 September, 2023; originally announced September 2023.

Comments: 34 pages, 13 figures. The codes are available at https://github.com/TianQinSYSU/GWSpace. Update to match published version

Journal ref: Class.Quant.Grav. 42 (2025) 16, 165005

Near Real-Time Gravitational Wave Data Analysis of the Massive Black Hole Binary with TianQin

Authors: Hong-Yu Chen, Xiang-Yu Lyu, En-Kun Li, Yi-Ming Hu

Abstract: Space-borne gravitational wave (GW) detectors can detect the merger of massive black holes. The early warning and localization of GW events before merging can be used to inform electromagnetic telescopes and conduct multimessenger observations. However, this requires real-time data transmission and analysis capabilities. The geocentric orbit of the space-borne GW detector TianQin makes it possible… ▽ More Space-borne gravitational wave (GW) detectors can detect the merger of massive black holes. The early warning and localization of GW events before merging can be used to inform electromagnetic telescopes and conduct multimessenger observations. However, this requires real-time data transmission and analysis capabilities. The geocentric orbit of the space-borne GW detector TianQin makes it possible to conduct real-time data transmission. In this study, we develop a search and localization pipeline for massive black hole binaries (MBHBs) with TianQin under both regular and real-time data transmission modes. We demonstrate that, with real-time data transmission, MBHBs can be accurately localized on the fly. With the approaching merger, each analysis can be finished in only 40 min. For an MBHB system at a distance of 1 Gpc, if we receive data every hour, then we can pinpoint its location to within less than 1 deg$^2$ on the final day before the merger. △ Less

Submitted 14 June, 2024; v1 submitted 13 September, 2023; originally announced September 2023.

Journal ref: Sci. China-Phys. Mech. Astron. 67, 279512 (2024)

Parameter Estimation of Stellar Mass Binary Black Holes under the Network of TianQin and LISA

Authors: Xiangyu Lyu, En-Kun Li, Yi-Ming Hu

Abstract: We present a Bayesian parameter estimation progress to infer the stellar mass binary black hole properties by TianQin, LISA, and TianQin+LISA.Two typical stellar mass black hole binary systems, GW150914 and GW190521 are chosen as the fiducial sources. In this work, we establish the ability of TianQin to infer the parameters of those systems and first apply the full frequency response in TianQin's… ▽ More We present a Bayesian parameter estimation progress to infer the stellar mass binary black hole properties by TianQin, LISA, and TianQin+LISA.Two typical stellar mass black hole binary systems, GW150914 and GW190521 are chosen as the fiducial sources. In this work, we establish the ability of TianQin to infer the parameters of those systems and first apply the full frequency response in TianQin's data analysis. We obtain the parameter estimation results and explain the correlation between them. We also find the TianQin+LISA could marginally increase the parameter estimation precision and narrow the $1σ$ area compared with TianQin and LISA individual observations. We finally demonstrate the importance of considering the effect of spin when the binaries have a nonzero component spin and great deviation will appear especially on mass, coalescence time and sky location. △ Less

Submitted 7 December, 2023; v1 submitted 23 July, 2023; originally announced July 2023.

Comments: 17 pages, 6 figures,

Journal ref: Phys. Rev. D 2023

Sensitivity to anisotropic stochastic gravitational-wave background with space-borne networks

Authors: Zheng-Cheng Liang, Zhi-Yuan Li, En-Kun Li, Jian-dong Zhang, Yi-Ming Hu

Abstract: Single gravitational-wave detectors face inherent limitations in detecting the anisotropy of the stochastic background. In this work, we explore the sensitivity to anisotropic backgrounds with a network of space-borne detectors. We find that the separation between detectors plays an important role in determining the sensitivity. For the first time, we observe as large as three orders of magnitude… ▽ More Single gravitational-wave detectors face inherent limitations in detecting the anisotropy of the stochastic background. In this work, we explore the sensitivity to anisotropic backgrounds with a network of space-borne detectors. We find that the separation between detectors plays an important role in determining the sensitivity. For the first time, we observe as large as three orders of magnitude enhancement in detection sensitivity for the multipoles with $l=5$ and 6, compared to coinciding detectors. Coordinating and optimizing the separation between two space-borne detectors can significantly enhance the network's sensitivity to the multipole components of the stochastic background. For the TianQin + LISA network, benefiting from detector separation, it is possible to achieve sensitivity levels of 2-3 orders of magnitude better than using TianQin or LISA detector alone. These findings pave the way to uncover the underlying physics of anisotropy through gravitational-wave detections. △ Less

Submitted 20 August, 2024; v1 submitted 4 July, 2023; originally announced July 2023.

Comments: 19 pages, 13 figures

Measuring the Hubble Constant Using Strongly Lensed Gravitational Wave Signals

Authors: Shun-Jia Huang, Yi-Ming Hu, Xian Chen, Jian-dong Zhang, En-Kun Li, Zucheng Gao, Xin-Yi Lin

Abstract: The measurement of the Hubble constant $H_0$ plays an important role in the study of cosmology. In this letter, we propose a new method to constrain the Hubble constant using the strongly lensed gravitational wave (GW) signals. By reparameterizing the waveform, we find that the lensed waveform is sensitive to the $H_0$. Assuming the scenario that no electromagnetic counterpart of the GW source can… ▽ More The measurement of the Hubble constant $H_0$ plays an important role in the study of cosmology. In this letter, we propose a new method to constrain the Hubble constant using the strongly lensed gravitational wave (GW) signals. By reparameterizing the waveform, we find that the lensed waveform is sensitive to the $H_0$. Assuming the scenario that no electromagnetic counterpart of the GW source can be identified, our method can still give meaningful constraints on the $H_0$ with the information of the lens redshift. We then apply Fisher information matrix and Markov Chain Monte Carlo to evaluate the potential of this method. For the space-based GW detector, TianQin, the $H_0$ can be constrained within a relative error of $\sim$ 0.3-2\%, using a single strongly lensed GW event. Precision varies according to different levels of electromagnetic information. △ Less

Submitted 8 August, 2023; v1 submitted 20 April, 2023; originally announced April 2023.

Comments: 8 pages, 4 figures

Journal ref: JCAP08(2023)003

Measurement of $^{19}$F($p$,$γ$)$^{20}$Ne reaction suggests CNO break-out in first stars

Authors: Liyong Zhang, Jianjun He, Richard J. deBoer, Michael Wiescher, Alexander Heger, Daid Kahl, Jun Su, Daniel Odell, Yinji Chen, Xinyue Li, Jianguo Wang, Long Zhang, Fuqiang Cao, Hao Zhang, Zhicheng Zhang, Xinzhi Jiang, Luohuan Wang, Ziming Li, Luyang Song, Hongwei Zhao, Liangting Sun, Qi Wu, Jiaqing Li, Baoqun Cui, Lihua Chen , et al. (11 additional authors not shown)

Abstract: The origin of calcium production in the first stars (Pop III stars), which formed out of the primordial matter of the Big Bang, and their fates, remain most fascinating mysteries in astrophysics. Advanced nuclear burning and supernovae were thought to be the dominant source of the Ca production seen in all stars. Here we report on a qualitatively different path to Ca production through break-out f… ▽ More The origin of calcium production in the first stars (Pop III stars), which formed out of the primordial matter of the Big Bang, and their fates, remain most fascinating mysteries in astrophysics. Advanced nuclear burning and supernovae were thought to be the dominant source of the Ca production seen in all stars. Here we report on a qualitatively different path to Ca production through break-out from the "warm" carbon-nitrogen-oxygen (CNO) cycle. We extend direct measurement of the $^{19}$F($p$, $γ$)$^{20}$Ne break-out reaction down to an unprecedentedly low energy point of 186 keV and discover a key resonance at 225 keV. In the domain of astrophysical interest, at around 0.1 giga kelvin, this thermonuclear $^{19}$F($p$,$γ$)$^{20}$Ne rate is up to a factor of 7.4 larger than the previous recommended rate. Our stellar models show a stronger break-out during stellar hydrogen burning than thought before, and may reveal the nature of Ca production in Pop III stars imprinted on the oldest known ultra-iron poor star, SMSS0313-6708. This result from the China Jinping Underground Laboratory, the deepest laboratory in the world, offering an environment with extremely low cosmic-ray induced background, has far-reaching implications on our understanding of how the first stars evolve and die. Our rate showcases the impact that faint Pop III star supernovae can have on the nucleosynthesis observed in the oldest known stars and first galaxies, key mission targets of the James Webb Space Telescope. △ Less

Submitted 20 February, 2023; originally announced February 2023.

Comments: 32 pages, 8 figures, 6 tables

Journal ref: Nature 610 (2022) p656

Data-driven and Almost Model-independent Reconstruction of Modified Gravity

Authors: Yuhao Mu, En-Kun Li, Lixin Xu

Abstract: In this paper, a modified factor $μ$, which characterizes modified gravity in the linear matter density perturbation theory, is reconstructed in a data-driven and almost model-independent way via Gaussian process by using currently available cosmic observations. Utilizing the Pantheon+ SNe Ia samples, the observed Hubble parameter $H(z)$ and the redshift space distortion $fσ_8(z)$ data points, one… ▽ More In this paper, a modified factor $μ$, which characterizes modified gravity in the linear matter density perturbation theory, is reconstructed in a data-driven and almost model-independent way via Gaussian process by using currently available cosmic observations. Utilizing the Pantheon+ SNe Ia samples, the observed Hubble parameter $H(z)$ and the redshift space distortion $fσ_8(z)$ data points, one finds out a time varying $μ$ at low redshifts. The reconstructed $μ$ implies that more complicated modified gravity beyond the simplest general relativity and the Dvali-Gabadadze-Porrati braneworld model is required. △ Less

Submitted 10 September, 2023; v1 submitted 20 February, 2023; originally announced February 2023.

Comments: 14 pages, 3 figures

Journal ref: JCAP06(2023)022

Impact of combinations of time-delay interferometry channels on stochastic gravitational wave background detection

Authors: Zheng-Cheng Liang, Zhi-Yuan Li, Jun Cheng, En-Kun Li, Jian-dong Zhang, Yi-Ming Hu

Abstract: The method of time delay interferometry (TDI) is proposed to cancel the laser noise in space-borne gravitational-wave detectors. Among all different TDI combinations, the most commonly used ones are the orthogonal channels A, E and T, where A and E are signal-sensitive and T is signal-insensitive. Meanwhile, for the detection of stochastic gravitational-wave background, one needs to introduce the… ▽ More The method of time delay interferometry (TDI) is proposed to cancel the laser noise in space-borne gravitational-wave detectors. Among all different TDI combinations, the most commonly used ones are the orthogonal channels A, E and T, where A and E are signal-sensitive and T is signal-insensitive. Meanwhile, for the detection of stochastic gravitational-wave background, one needs to introduce the overlap reduction function to characterize the correlation between channels. For the calculation of overlap reduction function, it is often convenient to work in the low-frequency approximation, and assuming the equal-arm Michelson channels. However, if one wishes to work on the overlap reduction function of $\rm A/E$ channels, then the low-frequency approximation fails. We derive the exact form of overlap reduction function for $\rm A/E$ channels. Based on the overlap reduction function, we calculate the sensitivity curves of TianQin, TianQin I+II and TianQin + LISA. We conclude that the detection sensitivity calculated with $\rm A/E$ channels is mostly consistent with that obtained from the equal-arm Michelson channels. △ Less

Submitted 22 May, 2023; v1 submitted 6 December, 2022; originally announced December 2022.

Comments: 18 pages,10 figures

Journal ref: Phys.Rev.D 107 (2023) 8, 083033

Measurement of the $^{159}$Tb(n, $γ$) cross section at the CSNS Back-n facility

Authors: S. Zhang, G. Li, W. Jiang, D. X. Wang, J. Ren, E. T. Li, M. Huang, J. Y. Tang, X. C. Ruan, H. W. Wang, Z. H. Li, Y. S. Chen, L. X. Liu, X. X. Li, Q. W. Fan, R. R. Fan, X. R. Hu, J. C. Wang, X. Li, 1D. D. Niu, N. Song, M. Gu

Abstract: The stellar (n, $γ$) cross section data for the mass numbers around A $\approx$ 160 are of key importance to nucleosynthesis in the main component of the slow neutron capture process, which occur in the thermally pulsing asymptotic giant branch (TP--AGB). The new measurement of (n, $γ$) cross sections for $^{159}$Tb was performed using the C$_6$D$_6$ detector system at the back streaming white neu… ▽ More The stellar (n, $γ$) cross section data for the mass numbers around A $\approx$ 160 are of key importance to nucleosynthesis in the main component of the slow neutron capture process, which occur in the thermally pulsing asymptotic giant branch (TP--AGB). The new measurement of (n, $γ$) cross sections for $^{159}$Tb was performed using the C$_6$D$_6$ detector system at the back streaming white neutron beam line (Back-n) of the China spallation neutron source (CSNS) with neutron energies ranging from 1 eV to 1 MeV. Experimental resonance capture kernels were reported up to 1.2 keV neutron energy with this capture measurement. Maxwellian-averaged cross sections (MACS) were derived from the measured $^{159}$Tb (n, $γ$) cross sections at $kT$ = 5 $\sim$ 100 keV and are in good agreement with the recommended data of KADoNiS-v0.3 and JEFF-3.3, while KADoNiS-v1.0 and ENDF-VIII.0 significantly overestimate the present MACS up to 40$\%$ and 20$\%$, respectively. A sensitive test of the s-process nucleosynthesis was also performed with the stellar evolution code MESA. Significant changes in abundances around A $\approx$ 160 were observed between the ENDF/B-VIII.0 and present measured rate of $^{159}$Tb(n, $γ$)$^{160}$Tb in the MESA simulation. △ Less

Submitted 4 December, 2022; originally announced December 2022.

Comments: 13 pages, 7 figures

Detecting the stochastic gravitational wave background with the TianQin detector

Authors: Jun Cheng, En-Kun Li, Yi-Ming Hu, Zheng-Cheng Liang, Jian-dong Zhang, Jianwei Mei

Abstract: The detection of stochastic gravitational wave background (SGWB) is among the leading scientific goals of the space-borne gravitational wave observatory, which would have significant impact on astrophysics and fundamental physics. In this work, we developed a data analysis software, \texttt{TQSGWB}, which can extract isotropic SGWB using the Bayes analysis method based on the TianQin detector. We… ▽ More The detection of stochastic gravitational wave background (SGWB) is among the leading scientific goals of the space-borne gravitational wave observatory, which would have significant impact on astrophysics and fundamental physics. In this work, we developed a data analysis software, \texttt{TQSGWB}, which can extract isotropic SGWB using the Bayes analysis method based on the TianQin detector. We find that for the noise cross spectrum, there are imaginary components and they play an important role in breaking the degeneracy of the position noise in the common laser link. When the imaginary corrections are considered, the credible regions of the position noise parameters are reduced by two orders of magnitude. We demonstrate that the parameters of various signals and instrumental noise could be estimated directly in the absence of a Galactic confusion foreground through Markov chain Monte Carlo sampling. With only a three-month observation, we find that TianQin could be able to confidently detect SGWBs with energy density as low as $Ω_{\rm PL} = 1.3 \times 10^{-12}$, $Ω_{\rm Flat} = 6.0 \times 10^{-12}$, and $Ω_{\rm SP} = 9.0 \times 10^{-12}$, for power-law, flat, and single-peak models respectively. △ Less

Submitted 4 December, 2022; v1 submitted 24 August, 2022; originally announced August 2022.

Comments: 28 pages, 8 figures

An implementation of Galactic white dwarf binary data analysis for MLDC-3.1

Authors: Yang Lu, En-Kun Li, Yi-Ming Hu, Jian-dong Zhang, Jianwei Mei

Abstract: The space-borne gravitational wave detectors will observe a large population of double white dwarf binaries in the Milky Way. However, the search for double white dwarfs in the gravitational wave data will be time-consuming due to the large number of templates involved and antenna response calculation. In this paper, we implement an iterative combinatorial algorithm to search for double white dwar… ▽ More The space-borne gravitational wave detectors will observe a large population of double white dwarf binaries in the Milky Way. However, the search for double white dwarfs in the gravitational wave data will be time-consuming due to the large number of templates involved and antenna response calculation. In this paper, we implement an iterative combinatorial algorithm to search for double white dwarfs in MLDC-3.1 data. To quickly determine the rough parameters of the target sources, the following algorithms are adopted in a coarse search process: (1) using the downsampling method to reduce the number of original data points; (2) using the undersampling method to speed up the generation of a single waveform template; (3) using the stochastic template bank method to quickly construct the waveform template bank while achieving high coverage of the parameter space; (4) Combining the FFT acceleration algorithm with the stochastic template bank to reduce the calculation time of a single template. A fine search process is applied to further determine the parameters of the signals based on the coarse search, for which we adopt the particle swarm optimization. Finally, we detected $\mathcal{O}(10^4)$ double white dwarf signals, validating the feasibility of our method. △ Less

Submitted 7 February, 2023; v1 submitted 4 May, 2022; originally announced May 2022.

Comments: 16 pages, 15 figures

Constraining the Hubble constant to a precision of about 1% using multi-band dark standard siren detections

Authors: Liang-Gui Zhu, Ling-Hua Xie, Yi-Ming Hu, Shuai Liu, En-Kun Li, Nicola R. Napolitano, Bai-Tian Tang, Jian-dong Zhang, Jianwei Mei

Abstract: Gravitational wave signal from the inspiral of stellar-mass binary black hole can be used as standard sirens to perform cosmological inference. This inspiral covers a wide range of frequency bands, from the millihertz band to the audio-band, allowing for detections by both space-borne and ground-based gravitational wave detectors. In this work, we conduct a comprehensive study on the ability to co… ▽ More Gravitational wave signal from the inspiral of stellar-mass binary black hole can be used as standard sirens to perform cosmological inference. This inspiral covers a wide range of frequency bands, from the millihertz band to the audio-band, allowing for detections by both space-borne and ground-based gravitational wave detectors. In this work, we conduct a comprehensive study on the ability to constrain the Hubble constant using the dark standard sirens, or gravitational wave events that lack electromagnetic counterparts. To acquire the redshift information, we weight the galaxies within the localization error box with photometric information from several bands and use them as a proxy for the binary black hole redshift. We discover that TianQin is expected to constrain the Hubble constant to a precision of roughly $30\%$ through detections of $10$ gravitational wave events; in the most optimistic case, the Hubble constant can be constrained to a precision of $< 10 \%$, assuming TianQin I+II. In the optimistic case, the multi-detector network of TianQin and LISA is capable of constraining the Hubble constant to within $5\%$ precision. It is worth highlighting that the multi-band network of TianQin and Einstein Telescope is capable of constraining the Hubble constant to a precision of about $1\%$. We conclude that inferring the Hubble constant without bias from photo-z galaxy catalog is achievable, and we also demonstrate self-consistency using the P$-$P plot. On the other hand, high-quality spectroscopic redshift information is crucial for improving the estimation precision of Hubble constant. △ Less

Submitted 30 January, 2022; v1 submitted 11 October, 2021; originally announced October 2021.

Comments: 29 pages, 14 figures, update to match published version

The Radioactive Nuclei $^{\textbf{26}}$Al and $^{\textbf{60}}$Fe in the Cosmos and in the Solar System

Authors: Roland Diehl, Maria Lugaro, Alexander Heger, Andre Sieverding, Xiaodong Tang, KuoAng Li, Ertao Li, Carolyn L. Doherty, Martin G. H. Krause, Anton Wallner, Nikos Prantzos, Hannah E. Brinkman, Jaqueline W. den Hartogh, Benjamin Wehmeyer, Andrés Yagüe López, Moritz M. M. Pleintinger, Projjval Banerjee, Wei Wang

Abstract: The cosmic evolution of the chemical elements from the Big Bang to the present time is driven by nuclear fusion reactions inside stars and stellar explosions. A cycle of matter recurrently re-processes metal-enriched stellar ejecta into the next generation of stars. The study of cosmic nucleosynthesis and of this matter cycle requires the understanding of the physics of nuclear reactions, of the c… ▽ More The cosmic evolution of the chemical elements from the Big Bang to the present time is driven by nuclear fusion reactions inside stars and stellar explosions. A cycle of matter recurrently re-processes metal-enriched stellar ejecta into the next generation of stars. The study of cosmic nucleosynthesis and of this matter cycle requires the understanding of the physics of nuclear reactions, of the conditions at which the nuclear reactions are activated inside the stars and stellar explosions, of the stellar ejection mechanisms through winds and explosions, and of the transport of the ejecta towards the next cycle, from hot plasma to cold, star-forming gas. Due to the long timescales of stellar evolution, and because of the infrequent occurrence of stellar explosions, observational studies are challenging. Due to their radioactive lifetime of million years, the 26Al and 60Fe isotopes are suitable to characterise simultaneously the processes of nuclear fusion reactions and of interstellar transport. We describe and discuss the nuclear reactions involved in the production and destruction of 26Al and 60Fe, the key characteristics of the stellar sites of their nucleosynthesis and their interstellar journey after ejection from the nucleosynthesis sites. We connect the theoretical astrophysical aspects to the variety of astronomical messengers, from stardust and cosmic-ray composition measurements, through observation of gamma rays produced by radioactivity, to material deposited in deep-sea ocean crusts and to the inferred composition of the first solids that have formed in the Solar System. We show that considering measurements of the isotopic ratio of 26Al to 60Fe eliminate some of the unknowns when interpreting astronomical results, and discuss the lessons learned from these two isotopes on cosmic chemical evolution. △ Less

Submitted 5 October, 2021; v1 submitted 17 September, 2021; originally announced September 2021.

Comments: 51 pages, 44 figures; review from an ISSI workshop series; accepted for publication in PASA

Journal ref: Publications of the Astronomical Society of Australia , Volume 38 , 2021 , e062

Testing the effect of $H_0$ on $fσ_8$ tension using a Gaussian Process method

Authors: En-Kun Li, Minghui Du, Zhi-Huan Zhou, Hongchao Zhang, Lixin Xu

Abstract: Using the $fσ_8(z)$ redshift space distortion (RSD) data, the $σ_8^0-Ω_m^0$ tension is studied utilizing a parameterization of growth rate $f(z) = Ω_m(z)^γ$. Here, $f(z)$ is derived from the expansion history $H(z)$ which is reconstructed from the observational Hubble data applying the Gaussian Process method. It is found that different priors of $H_0$ have great influences on the evolution curve… ▽ More Using the $fσ_8(z)$ redshift space distortion (RSD) data, the $σ_8^0-Ω_m^0$ tension is studied utilizing a parameterization of growth rate $f(z) = Ω_m(z)^γ$. Here, $f(z)$ is derived from the expansion history $H(z)$ which is reconstructed from the observational Hubble data applying the Gaussian Process method. It is found that different priors of $H_0$ have great influences on the evolution curve of $H(z)$ and the constraint of $σ_8^0-Ω_m^0$. When using a larger $H_0$ prior, the low redshifts $H(z)$ deviate significantly from that of the $Λ$CDM model, which indicates that a dark energy model different from the cosmological constant can help to relax the $H_0$ tension problem. The tension between our best-fit values of $σ_8^0-Ω_m^0$ and that of the \textit{Planck} 2018 $Λ$CDM (PLA) will disappear (less than $1σ$) when taking a prior for $H_0$ obtained from PLA. Moreover, the tension exceeds $2σ$ level when applying the prior $H_0 = 73.52 \pm 1.62$ km/s/Mpc resulted from the Hubble Space Telescope photometry. By comparing the $S_8 -Ω_m^0$ planes of our method with the results from KV450+DES-Y1, we find that using our method and applying the RSD data may be helpful to break the parameter degeneracies. △ Less

Submitted 28 February, 2021; v1 submitted 27 November, 2019; originally announced November 2019.

Comments: 13 pages, 10 figures, accepted for publication by MNRAS

Evaluating the classification of Fermi BCUs from the 4FGL Catalog Using Machine Learning

Authors: Shi-Ju Kang, Enze Li, Wujing Ou, Kerui Zhu, Jun-Hui Fan, Qingwen Wu, Yue Yin

Abstract: The recently published fourth Fermi Large Area Telescope source catalog (4FGL) reports 5065 gamma-ray sources in terms of direct observational gamma-ray properties. Among the sources, the largest population is the Active Galactic Nuclei (AGN), which consists of 3137 blazars, 42 radio galaxies, and 28 other AGNs. The blazar sample comprises 694 flat-spectrum radio quasars (FSRQs), 1131 BL Lac-type… ▽ More The recently published fourth Fermi Large Area Telescope source catalog (4FGL) reports 5065 gamma-ray sources in terms of direct observational gamma-ray properties. Among the sources, the largest population is the Active Galactic Nuclei (AGN), which consists of 3137 blazars, 42 radio galaxies, and 28 other AGNs. The blazar sample comprises 694 flat-spectrum radio quasars (FSRQs), 1131 BL Lac-type objects (BL Lacs), and 1312 blazar candidates of an unknown type (BCUs). The classification of blazars is difficult using optical spectroscopy given the limited knowledge with respect to their intrinsic properties, and the limited availability of astronomical observations. To overcome these challenges, machine learning algorithms are being investigated as alternative approaches. Using the 4FGL catalog, a sample of 3137 Fermi blazars with 23 parameters is systematically selected. Three established supervised machine learning algorithms (random forests (RFs), support vector machines (SVMs), artificial neural networks (ANNs)) are employed to general predictive models to classify the BCUs. We analyze the results for all of the different combinations of parameters. Interestingly, a previously reported trend the use of more parameters leading to higher accuracy is not found. Considering the least number of parameters used, combinations of eight, 12 or 10 parameters in the SVM, ANN, or RF generated models achieve the highest accuracy (Accuracy $\simeq$ 91.8\%, or $\simeq$ 92.9\%). Using the combined classification results from the optimal combinations of parameters, 724 BL Lac type candidates and 332 FSRQ type candidates are predicted; however, 256 remain without a clear prediction. △ Less

Submitted 6 November, 2019; originally announced November 2019.

Comments: Accepted for publication in ApJ. 14 pages, 2 figures, 6 tables

Aluminium-26 from massive binary stars I: non-rotating models

Authors: H. E. Brinkman, C. L. Doherty, O. R. Pols, E. T. Li, B. Côté, M. Lugaro

Abstract: Aluminium-26 is a short-lived radionuclide with a half-life of 0.72Myr, which is observed today in the Galaxy via gamma-ray spectroscopy and is inferred to have been present in the early Solar System via analysis of meteorites. Massive stars are considered the main contributors of Al26. Although most massive stars are found in binary systems, the effect, however, of binary interactions on the Al26… ▽ More Aluminium-26 is a short-lived radionuclide with a half-life of 0.72Myr, which is observed today in the Galaxy via gamma-ray spectroscopy and is inferred to have been present in the early Solar System via analysis of meteorites. Massive stars are considered the main contributors of Al26. Although most massive stars are found in binary systems, the effect, however, of binary interactions on the Al26 yields have not been investigated since Braun & Langer (1995). Here we aim to fill this gap. We have used the MESA stellar evolution code to compute massive (10Msun<=M<=80Msun), non-rotating, single and binary stars of solar metallicity (Z=0.014). We computed the wind yields for the single stars and for the binary systems where mass transfer plays a major role. Depending on the initial mass of the primary star and orbital period, the Al26 yield can either increase or decrease in a binary system. For binary systems with primary masses up to ~35-40Msun, the yield can increase significantly, especially at the lower mass-end, while above ~45Msun the yield becomes similar to the single star yield or even decreases. Our preliminary results show that compared to supernova explosions, the contribution of mass-loss in binary systems to the total Al26 abundance produced by a stellar population is minor. On the other hand, if massive star mass-loss is the origin of Al26 in the early Solar System, our results will have significant implications for the identification of the potential stellar, or stellar population, source. △ Less

Submitted 10 September, 2019; originally announced September 2019.

Comments: 25 pages, 11 figures, 3 tables, accepted for publishing in ApJ

Detecting the neutrino mass and mass hierarchy from global data

Authors: Wenxue Zhang, En-Kun li, Minghui Du, Yuhao Mu, Shouli Ning, Baorong Chang, Lixin Xu

Abstract: In this paper, we have constrained the neutrino mass and mass hierarchy in the $Λ$CDM cosmology with the neutrino mass hierarchy parameter $Δ$, which represents different mass orderings, by using the {\it Planck} 2015 + BAO + SN + $H_{0}$ data set, together with the neutrino oscillation and neutrinoless double beta decay data. We find that the mass of the lightest neutrinos and the total neutrino… ▽ More In this paper, we have constrained the neutrino mass and mass hierarchy in the $Λ$CDM cosmology with the neutrino mass hierarchy parameter $Δ$, which represents different mass orderings, by using the {\it Planck} 2015 + BAO + SN + $H_{0}$ data set, together with the neutrino oscillation and neutrinoless double beta decay data. We find that the mass of the lightest neutrinos and the total neutrino mass are no more than $0.035$eV and $0.133$ eV at $95\%$ confidence level, respectively. Comparing the result of our joint analysis with that obtained using cosmological data alone, we find that, by adding the neutrino oscillation and neutrinoless double beta decay data, the tendency for normal hierarchy has increased a lot. By means of importance sampling, three other priors are taken into account, i.e., the flat logarithmic prior on the absolute value of the neutrino hierarchy parameter $Δ$, the flat linear prior on the total neutrino mass $Σm_ν$, and the flat logarithmic prior on $Σm_ν$. We find that the preference for the normal hierarchy is in agreement whatever what kinds of priors we choose. Finally, we make a Bayesian model analysis about four priors and we find that flat-linear and the flat logarithmic priors on $Σm_ν$ are the most favored priors. △ Less

Submitted 21 April, 2019; originally announced April 2019.

Comments: 15 pages, 3 figures

General Cosmography Model with Spatial Curvature

Authors: En-Kun Li, Minghui Du, Lixin Xu

Abstract: The cosmographic approach is adopted to determine the spatial curvature (i.e., $Ω_K$) combining the latest released cosmic chronometers data (CC), the Pantheon sample of type Ia supernovae observations, and the baryon acoustic oscillation measurements. We use the expanded transverse comoving distance $D_M(z)$ as a basic function for deriving $H(z)$ and the other cosmic distances. In this scenario,… ▽ More The cosmographic approach is adopted to determine the spatial curvature (i.e., $Ω_K$) combining the latest released cosmic chronometers data (CC), the Pantheon sample of type Ia supernovae observations, and the baryon acoustic oscillation measurements. We use the expanded transverse comoving distance $D_M(z)$ as a basic function for deriving $H(z)$ and the other cosmic distances. In this scenario, $Ω_K$ can be constrained only by CC data. To overcome the convergence issues at high-redshift domains, two methods are applied: the Padé approximants and the Taylor series in terms of the new redshift $y=z/(1+z)$. Adopting the Bayesian evidence, we find that there is positive evidence for the Padé approximant up to order ($2,2$) and weak evidence for the Taylor series up to 3-rd order against $Λ\text{CDM}+Ω_K$ model. The constraint results show that a closed universe is preferred by the present observations under all the approximants used in this study. And the tension level of the Hubble constant $H_0$ is less than $2σ$ significance between different approximants and the local distance ladder determination. For each assumed approximant, $H_0$ is anti-correlated with $Ω_K$ and the sound horizon at the end of the radiation drag epoch, which indicates that the $H_0$ tension problem can be slightly relaxed by introducing $Ω_K$ or any new physics which can reduce the sound horizon in the early universe. △ Less

Submitted 24 November, 2019; v1 submitted 27 March, 2019; originally announced March 2019.

Comments: 13 pages, 4 figures, major revised, update data and conclusions

The nature of the Li enrichment in the most Li-rich giant star

Authors: Hong-Liang Yan, Jian-Rong Shi, Yu-Tao Zhou, Yong-Shou Chen, Er-Tao Li, Suyalatu Zhang, Shao-Lan Bi, Ya-Qian Wu, Zhi-Hong Li, Bing Guo, Wei-Ping Liu, Qi Gao, Jun-Bo Zhang, Ze-Ming Zhou, Hai-Ning Li, Gang Zhao

Abstract: About one percent of giants\upcite{Brown1989} are detected to have anomalously high lithium (Li) abundances in their atmospheres, conflicting directly with the prediction of the standard stellar evolution models\upcite{Iben1967}, and making the production and evolution of Li more intriguing, not only in the sense of the Big Bang nucleosynthesis\upcite{Cyburt2016,Spite1982} or the Galactic medium\u… ▽ More About one percent of giants\upcite{Brown1989} are detected to have anomalously high lithium (Li) abundances in their atmospheres, conflicting directly with the prediction of the standard stellar evolution models\upcite{Iben1967}, and making the production and evolution of Li more intriguing, not only in the sense of the Big Bang nucleosynthesis\upcite{Cyburt2016,Spite1982} or the Galactic medium\upcite{Tajitsu2015}, but also the evolution of stars. Decades of efforts have been put into explaining why such outliers exist\upcite{Sackmann1999, Denissenkov2004, Charbonnel2010}, yet the origins of Li-rich giants are still being debated. Here we report the discovery of the most Li-rich giant known to date, with a super-high Li abundance of 4.51. This rare phenomenon was snapshotted together with another short-term event that the star is experiencing its luminosity bump on the red giant branch. Such high Li abundance indicates that the star might be at the very beginning of its Li-rich phase, which provides a great opportunity to investigate the origin and evolution of Li in the Galaxy. A detailed nuclear simulation is presented with up-to-date reaction rates to recreate the Li enriching process in this star. Our results provide tight constraints on both observational and theoretical points of view, suggesting that low-mass giants can produce Li inside themselves to a super high level via $^{7}$Be transportation during the red giant phase. △ Less

Submitted 1 September, 2018; originally announced September 2018.

Comments: 17 pages, 6 figures

Probing the Neutrino Mass Hierarchy beyond $Λ$CDM Model

Authors: En-Kun Li, Hongchao Zhang, Minghui Du, Zhi-Huan Zhou, Lixin Xu

Abstract: Taking the neutrino oscillation data into consideration, a dimensionless parameter $Δ= (m_3-m_1)/(m_3+m_1)$ is adopted to parameterize the three neutrino mass eigenstates and the normal (positive $Δ$) or inverted (negative $Δ$) mass hierarchies in three typical cosmological models. Using the currently available cosmic observational data, several Markov Chain Monte Carlo chains are obtained with un… ▽ More Taking the neutrino oscillation data into consideration, a dimensionless parameter $Δ= (m_3-m_1)/(m_3+m_1)$ is adopted to parameterize the three neutrino mass eigenstates and the normal (positive $Δ$) or inverted (negative $Δ$) mass hierarchies in three typical cosmological models. Using the currently available cosmic observational data, several Markov Chain Monte Carlo chains are obtained with uniform priors on the free parameters at first. Applying importance sampling the results are compared with three new priors, i.e., logarithmic prior on $|Δ|$, linear and logarithmic priors on $Σm_ν$. It turns out that the three new priors increase the upper limits of neutrino mass, but do not change the tendency towards different model's preference for different hierarchies, i.e., the normal hierarchy tends to be favored by $Λ$CDM and $w$CDM, which, however, disappears in the $w_0 w_a$CDM model. In addition, the almost symmetrical contours in the $w-Δ$, $w_0-Δ$, $w_a-Δ$ planes indicate that the normal and inverted hierarchy have strong degeneracy. Finally, we perform a Bayesian model comparison analysis, finding that flat linear prior on $Δ$ and $w_0 w_a$CDM are the most preferred prior and model, respectively. △ Less

Submitted 29 August, 2018; v1 submitted 4 March, 2017; originally announced March 2017.

Comments: 14 pages, 8 figures, accept to publish in JCAP. Revised to match the final type

Modelling mass distribution of the Milky Way galaxy using Gaia billion-star map

Authors: Enbang Li

Abstract: The Milky Way galaxy is a typical spiral galaxy which consists of a black hole in its centre, a barred bulge and a disk which contains spiral arms. The complex structure of the Galaxy makes it extremely difficult and challenging to model its mass distribution, particularly for the Galactic disk which plays the most important role in the dynamics and evolution of the Galaxy. Conventionally an axisy… ▽ More The Milky Way galaxy is a typical spiral galaxy which consists of a black hole in its centre, a barred bulge and a disk which contains spiral arms. The complex structure of the Galaxy makes it extremely difficult and challenging to model its mass distribution, particularly for the Galactic disk which plays the most important role in the dynamics and evolution of the Galaxy. Conventionally an axisymmetric disk model with an exponential brightness distribution and a constant mass-to-light ratio is assumed for the Galactic disk. In order to generate a flat rotation curve, a dark halo has also to be included. Here, by using the recently released Gaia billion-star map, we propose a Galactic disk mass distribution model which is based on the star density distribution rather than the brightness and mass-to-light ratio. The model is characterized by two parameters, a bulge radius and a characteristic length. Using the mass distribution model and solving the Poisson equation of the Galaxy, we obtain a flat rotation curve which reproduces the key observed features with no need for a dark halo. △ Less

Submitted 14 December, 2016; originally announced December 2016.

Comments: 11 pages, 3 figures

Distinguish three time-dependent dark energy models using statefinder pairs with error bars and Bayesian evidence

Authors: Hongchao Zhang, Enkun Li, Lixin Xu

Abstract: In this work, two completely different approaches, statefinder with error bars and Bayesian evidence, are used to distinguish and judge three time-dependent dark energy models. The parameters constrain for the three dark energy models are given using the current cosmic observational data sets : $Planck$ 2015, SNIa, BAO and OHD. Using the statefinder pairs with error bars, we find that the error re… ▽ More In this work, two completely different approaches, statefinder with error bars and Bayesian evidence, are used to distinguish and judge three time-dependent dark energy models. The parameters constrain for the three dark energy models are given using the current cosmic observational data sets : $Planck$ 2015, SNIa, BAO and OHD. Using the statefinder pairs with error bars, we find that the error region of the dark energy model, whose equation of state parameter is given by $w(a) = w_0+w_3\frac{1-a}{a^2+(1-a)^2}$, is relativity compact than the other two models during the all the evolving history. Meanwhile, the Bayesian evidence also provide that this model is significantly better than the other two models and the other two models are inconclusive. Then, there are reasons for believing that this model is a preferential candidate in dark energy investigation rather than the other two. △ Less

Submitted 12 October, 2016; v1 submitted 1 May, 2016; originally announced May 2016.

Comments: 9 pages, 10 figures, 4 tables

Modified holographic Ricci dark energy coupled to interacting relativistic and non-relativistic dark matter in the nonflat universe

Authors: En-Kun Li, Yu Zhang, Jin-Ling Geng

Abstract: The modified holographic Ricci dark energy coupled to interacting relativistic and non-relativistic dark matter is considered in the nonflat Friedmann-Robertson-Walker universe. Through examining the deceleration parameter, one can find that the transition time of the Universe from decelerating to accelerating phase in the interacting holographic Ricci dark energy model is close to that in the… ▽ More The modified holographic Ricci dark energy coupled to interacting relativistic and non-relativistic dark matter is considered in the nonflat Friedmann-Robertson-Walker universe. Through examining the deceleration parameter, one can find that the transition time of the Universe from decelerating to accelerating phase in the interacting holographic Ricci dark energy model is close to that in the $Λ$ cold dark matter model. The evolution of modified holographic Ricci dark energy's state parameter and the evolution of dark matter and dark energy's densities shows that the dark energy holds the dominant position from the near past to the future. By studying the statefinder diagnostic and the evolution of the total pressure, one can find that this model could explain the Universe's transition from the radiation to accelerating expansion stage through the dust stage. According to the $Om$ diagnostic, it is easy to find that when the interaction is weak and the proportion of relativistic dark matter in total dark matter is small, this model is phantom-like. Through our studying, we find the interaction and the relativistic dark matter's proportion all have great influence on the evolution of the Universe. △ Less

Submitted 16 December, 2014; originally announced December 2014.

Comments: 14 pages, 8 figures

Journal ref: Phys. Rev. D 90, 083534 (2014)

Constraining nova observables: direct measurements of resonance strengths in 33S(p,γ)34Cl

Authors: J. Fallis, A. Parikh, P. F. Bertone, S. Bishop, L. Buchmann, A. A. Chen, G. Christian, J. A. Clark, J. M. D'Auria, B. Davids, C. M. Deibel, B. R. Fulton, U. Greife, B. Guo, U. Hager, C. Herlitzius, D. A. Hutcheon, J. José, A. M. Laird, E. T. Li, Z. H. Li, G. Lian, W. P. Liu, L. Martin, K. Nelson , et al. (10 additional authors not shown)

Abstract: The 33S(p,γ)34Cl reaction is important for constraining predictions of certain isotopic abundances in oxygen-neon novae. Models currently predict as much as 150 times the solar abundance of 33S in oxygen-neon nova ejecta. This overproduction factor may, however, vary by orders of magnitude due to uncertainties in the 33S(p,γ)34Cl reaction rate at nova peak temperatures. Depending on this rate, 33S… ▽ More The 33S(p,γ)34Cl reaction is important for constraining predictions of certain isotopic abundances in oxygen-neon novae. Models currently predict as much as 150 times the solar abundance of 33S in oxygen-neon nova ejecta. This overproduction factor may, however, vary by orders of magnitude due to uncertainties in the 33S(p,γ)34Cl reaction rate at nova peak temperatures. Depending on this rate, 33S could potentially be used as a diagnostic tool for classifying certain types of presolar grains. Better knowledge of the 33S(p,γ)34Cl rate would also aid in interpreting nova observations over the S-Ca mass region and contribute to the firm establishment of the maximum endpoint of nova nucleosynthesis. Additionally, the total S elemental abundance which is affected by this reaction has been proposed as a thermometer to study the peak temperatures of novae. Previously, the 33S(p,γ)34Cl reaction rate had only been studied directly down to resonance energies of 432 keV. However, for nova peak temperatures of 0.2-0.4 GK there are 7 known states in 34Cl both below the 432 keV resonance and within the Gamow window that could play a dominant role. Direct measurements of the resonance strengths of these states were performed using the DRAGON recoil separator at TRIUMF. Additionally two new states within this energy region are reported. Several hydrodynamic simulations have been performed, using all available experimental information for the 33S(p,γ)34Cl rate, to explore the impact of the remaining uncertainty in this rate on nucleosynthesis in nova explosions. These calculations give a range of ~ 20-150 for the expected 33S overproduction factor, and a range of ~ 100-450 for the 32S/33S ratio expected in ONe novae. △ Less

Submitted 13 September, 2013; originally announced September 2013.

Comments: 12 pages, 8 figures, Accepted for publication in Physical Review C

New determination of the 13C(a, n)16O reaction rate and its influence on the s-process nucleosynthesis in AGB stars

Authors: B. Guo, Z. H. Li, M. Lugaro, J. Buntain, D. Y. Pang, Y. J. Li, J. Su, S. Q. Yan, X. X. Bai, Y. S. Chen, Q. W. Fan, S. J. Jin, A. I. Karakas, E. T. Li, Z. C. Li, G. Lian, J. C. Liu, X. Liu, J. R. Shi, N. C. Shu, B. X. Wang, Y. B. Wang, S. Zeng, W. P. Liu

Abstract: We present a new measurement of the $α$-spectroscopic factor ($S_α$) and the asymptotic normalization coefficient (ANC) for the 6.356 MeV 1/2$^+$ subthreshold state of $^{17}$O through the $^{13}$C($^{11}$B, $^{7}$Li)$^{17}$O transfer reaction and we determine the $α$-width of this state. This is believed to have a strong effect on the rate of the $^{13}$C($α$, $n$)$^{16}$O reaction, the main neut… ▽ More We present a new measurement of the $α$-spectroscopic factor ($S_α$) and the asymptotic normalization coefficient (ANC) for the 6.356 MeV 1/2$^+$ subthreshold state of $^{17}$O through the $^{13}$C($^{11}$B, $^{7}$Li)$^{17}$O transfer reaction and we determine the $α$-width of this state. This is believed to have a strong effect on the rate of the $^{13}$C($α$, $n$)$^{16}$O reaction, the main neutron source for {\it slow} neutron captures (the $s$-process) in asymptotic giant branch (AGB) stars. Based on the new width we derive the astrophysical S-factor and the stellar rate of the $^{13}$C($α$, $n$)$^{16}$O reaction. At a temperature of 100 MK our rate is roughly two times larger than that by \citet{cau88} and two times smaller than that recommended by the NACRE compilation. We use the new rate and different rates available in the literature as input in simulations of AGB stars to study their influence on the abundances of selected $s$-process elements and isotopic ratios. There are no changes in the final results using the different rates for the $^{13}$C($α$, $n$)$^{16}$O reaction when the $^{13}$C burns completely in radiative conditions. When the $^{13}$C burns in convective conditions, as in stars of initial mass lower than $\sim$2 $M_\sun$ and in post-AGB stars, some changes are to be expected, e.g., of up to 25% for Pb in our models. These variations will have to be carefully analyzed when more accurate stellar mixing models and more precise observational constraints are available. △ Less

Submitted 3 August, 2012; originally announced August 2012.

Journal ref: Astrophys. J. 756, 193, 2012

Investigation of excited states in $^{18}$Ne via resonant elastic scattering of $^{17}$F+p and its astrophysical implication in the stellar reaction of $^{14}$O($α$,$p$)$^{17}$F

Authors: J. Hu, J. J. He, S. W. Xu, Z. Q. Chen, X. Y. Zhang, J. S. Wang, X. Q. Yu, L. Li, L. Y. Zhang, Y. Y. Yang, P. Ma, X. H. Zhang, Z. G. Hu, Z. Y. Guo, X. Xu, X. H. Yuan, W. Lu, Y. H. Yu, Y. D. Zang, S. W. Tang, R. P. Ye, J. D. Chen, S. L. Jin, C. M. Du, S. T. Wang , et al. (13 additional authors not shown)

Abstract: Properties of proton resonances in $^{18}$Ne have been investigated efficiently by utilizing a technique of proton resonant elastic scattering with a $^{17}$F radioactive ion (RI) beam and a thick proton target. A 4.22~MeV/nucleon $^{17}$F RI beam was produced via a projectile-fragmentation reaction, and subsequently separated by a Radioactive Ion Beam Line in Lanzhou ({\tt RIBLL}). Energy spectra… ▽ More Properties of proton resonances in $^{18}$Ne have been investigated efficiently by utilizing a technique of proton resonant elastic scattering with a $^{17}$F radioactive ion (RI) beam and a thick proton target. A 4.22~MeV/nucleon $^{17}$F RI beam was produced via a projectile-fragmentation reaction, and subsequently separated by a Radioactive Ion Beam Line in Lanzhou ({\tt RIBLL}). Energy spectra of the recoiled protons were measured by two sets of $Δ$E-E silicon telescope at center-of-mass scattering angles of $θ_{c.m.}$$\approx$175${^\circ}$$\pm$5${^\circ}$, $θ_{c.m.}$$\approx$152${^\circ}$$\pm$8${^\circ}$, respectively. Several proton resonances in $^{18}$Ne were observed, and their resonant parameters have been determined by an $R$-matrix analysis of the differential cross sections in combination with the previous results. The resonant parameters are related to the reaction-rate calculation of the stellar $^{14}$O($α$,$p$)$^{17}$F reaction, which was thought to be the breakout reaction from the hot CNO cycles into the $rp$-process in x-ray bursters. Here, $J^π$=(3$^-$, 2$^-$) are tentatively assigned to the 6.15-MeV state which was thought the key 1$^-$ state previously. In addition, a doublet structure at 7.05 MeV are tentatively identified, and its contribution to the resonant reaction rate of $^{14}$O($α$,$p$)$^{17}$F could be enhanced by at least factors of about 4$\sim$6 in comparison with the previous estimation involving only a singlet. The present calculated resonant rates are much larger than those previous values, and it may imply that this breakout reaction could play a crucial role under x-ray bursters conditions. △ Less

Submitted 7 September, 2010; originally announced September 2010.

Comments: 8 figures, 2 tables