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  • Formation of millisecond pulsars with long orbital periods by accretion-induced collapse of white-dwarfs

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Accretion-induced collapse (AIC) of massive white-dwarfs (WDs) has been proposed as an important way for the formation of neutron star (NS) systems. An oxygen-neon (ONe) WD that accretes H-rich material from a red-giant (RG) star may experience the AIC process, eventually producing millisecond pulsars (MSPs), known as the RG donor channel. Previous studies indicate that this channel can only account for MSPs with orbital periods $>500\,\rm d$. It is worth noting that some more MSPs with wide orbits ($60-500\,\rm d$) have been detected by recent observations, but their origin is still highly uncertain. In the present work, by employing an adiabatic power-law assumptions for the mass-transfer process, we performed a large number of complete binary evolution calculations for the formation of MSPs through the RG donor channel in a systematic way. We found that this channel can contribute to the observed MSPs with orbital periods in the range of $50-1200\,{\rm d}$, and almost all the observed MSPs with wide orbits can be covered by this channel in the WD companion mass versus orbital period diagram. The present work indicates that the AIC process provides a viable way to form MSPs with wide orbits.

  • Helium enrichment during classical nova outbursts

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Nova outbursts play an important role in the chemical evolution of galaxies, especially they are the main source of synthetic $^{13}\rm C$, $^{15}\rm N$, $^{17}\rm O$ and some radioactive isotopes like $^{22}\rm Na$ and $^{26}\rm Al$. The enrichment of He in nova ejecta indicates that the accreted material may mix with the He-shell (He-mixing). The purpose of this work is to investigate how the He-mixing affects the nova outbursts in a systematic way. We evolved a series of accreting WD models, and found that the mass fraction of H and He in nova ejecta can be influenced by different He-mixing fractions significantly. We also found that both the nova cycle duration and ejected mass increase with the He-mixing fractions. Meanwhile, the nuclear energy production from $p$-$p$ chains decreases with the He-mixing fraction during the nova outbursts, whereas the CNO-cycle increases. The present work can reproduce the chemical abundances in the ejecta of some novae, such as GQ Mus, ASASSN-18fv, HR Del, T Aur and V443 Sct. This implies that the He-mixing process cannot be neglected when studying nova outbursts. This study also develops a He-mixing meter (i.e. $\rm He/H$) that can be used to estimate the He-mixing fraction in classical nova systems.

  • Formation of black widows through ultra-compact X-ray binaries with He star companions

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Black widows (BWs) are a type of eclipsing millisecond pulsars (MSPs) with companion masses $M_2$ $\lesssim 0.05\,\rm M_\odot$, which can be used to study the accretion history and the radiation of pulsars, as well as the origin of isolated MSPs. Recent observations indicate that there are two sub-types of BWs. One is the BWs with $M_2$ $\sim$ $0.01-0.05\,\rm M_\odot$, whereas another with $M_2$ $\lesssim 0.01\,\rm M_\odot$. However, the origin of the latter is still highly uncertain. In this paper, we investigated the formation of BWs with $M_2$ $\lesssim 0.01\,\rm M_\odot$ through ultra-compact X-ray binaries (UCXBs) with He star companions, in which a neutron star (NS) accretes material from a He star through Roche-lobe overflow. By considering different He star masses and evaporation efficiencies with the stellar evolution code Modules for Experiments in Stellar Astrophysics (MESA), we evolved a series of NS+He star systems that can undergo UCXB stage. We found that this channel can explain the formation of BWs with $M_2$ $\lesssim 0.01\,\rm M_\odot$ within the Hubble time, especially three widely studied BWs, i.e. PSRs J1719-1438, J2322-2650 and J1311-3430. We also found that X-ray irradiation feedback does not affect the evolutionary tracks of evaporation process. Our simulations indicate that the UCXB channel with He star companions are the potential progenitors of isolated MSPs, and that the origin of BWs with $M_2$ $\lesssim 0.01\,\rm M_\odot$ is different with another sub-type of BWs. In addition, the present work suggests that the BWs with $M_2$ $\lesssim 0.01\,\rm M_\odot$ may not be produced by redback systems.

  • Mixing fraction in classical novae

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Context. Classical novae are powered by thermonuclear runaways occurring on the surface of accreting white dwarfs (WDs). In the observations, the enrichments of heavy elements in nova ejecta have been detected, indicating a mixing process between the accreted matter and the matter from the outer layers of the underlying WDs prior to nova outbursts. However, the mixing fraction in classical novae is still uncertain. Aims. The purpose of this article is to investigate some elemental abundance ratios during nova outbursts that can be used to estimate the WD mixing fraction in classical novae. Methods. By considering different WD mixing fractions with the stellar evolution code Modules for Experiments in Stellar Astrophysics (MESA), we carried out a series of simulations of nova outbursts, in which the initial CO WD masses range from $0.7-1.0\,M_\odot$. Results. We identified four elemental abundance ratios (i.e. $\rm (H+He)/\sum CNO$, $\rm (H+He)/Ne$, $\rm \sum CNO/Mg,$ and $\rm \sum CNO/Si$) that satisfy the conditions for determining the WD mixing fraction, in which $\rm (H+He)/\sum CNO$ is the most suitable mixing meter. We also estimated the WD mixing fraction in some representative classical novae. Additionally, we found that a higher metallicity (i.e. higher WD mixing fraction) is preferentially accompanied by a longer $t_{\rm 2}$ (the time of decline by two magnitudes from peak luminosity) during nova outbursts. Our results can be used to constrain the mixing process in classical novae.

  • Indoor optical fiber eavesdropping approach and its avoidance

    分类: 光学 >> 量子光学 提交时间: 2023-02-19

    摘要: The optical fiber network has become a worldwide infrastructure. In addition to the basic functions in telecommunication, its sensing ability has attracted more and more attention. In this paper, we discuss the risk of household fiber being used for eavesdropping and demonstrate its performance in the lab. Using a 3-meter tail fiber in front of the household optical modem, voices of normal human speech can be eavesdropped by a laser interferometer and recovered 1.1 km away. The detection distance limit and system noise are analyzed quantitatively. We also give some practical ways to prevent eavesdropping through household fiber.

  • Prospects for Constraining interacting dark energy cosmology with gravitational-wave bright sirens detected by future SKA-era pulsar timing arrays

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Pulsar timing arrays (PTAs) have the potential to detect Nanohertz gravitational waves (GWs) that are usually generated by the individual inspiraling supermassive black hole binaries (SMBHBs) in the galactic centers. The GW signals as cosmological standard sirens can provide the absolute cosmic distances, thereby can be used to constrain the cosmological parameters. In this paper, we analyze the ability of future SKA-era PTAs to detect the existing SMBHBs candidates assuming the root mean square of timing noise $\sigma_t=20\ {\rm ns}$, and use the simulated PTA data to constrain the interacting dark energy (IDE) models with energy transfer rate $Q = \beta H\rho_c$. We find that, the future SKA-era PTAs will play an important role in constraining the IDE cosmology. Using only the mock PTA data consisting of 100 pulsars, we obtain $\sigma(H_0)=0.239\ {\rm km} \ {\rm s}^{-1} {\rm Mpc}^{-1}$ and $\sigma(\Omega_m)=0.0103$ in the I$\Lambda$CDM model, which are much better than the results from the Planck TT, TE, EE+lowE. However, the PTA data cannot provide a tight constraint on the coupling parameter $\beta$ compared with Planck, but the data combination of Planck+PTA can provide a rather tight constraint, i.e., $\sigma(\beta)=0.00232$, since the PTA data could break the parameter degeneracies inherent in CMB. In the I$w$CDM model, we obtain $\sigma(\beta)=0.00137$ and $\sigma(w)=0.0492$ from the Planck+PTA data combination. In addition, we also find that with the increase of the number of pulsars in PTA, the constraint results from the Planck+PTA will be further improved to some extent. We show that the observations of Nanohertz GWs with future SKA-era PTAs will provide a powerful tool for exploring the nature of dark energy and measuring the coupling between dark energy and dark matter.

  • Searching for cosmic string induced stochastic gravitational wave background with the Parkes Pulsar Timing Array

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We search for stochastic gravitational wave background emitted from cosmic strings using the Parkes Pulsar Timing Array data over 15 years. While we find that the common power-law excess revealed by several pulsar timing array experiments might be accounted for by the gravitational wave background from cosmic strings, the lack of the characteristic Hellings-Downs correlation cannot establish its physical origin yet. The constraints on the cosmic string model parameters are thus derived with conservative assumption that the common power-law excess is due to unknown background. Two representative cosmic string models with different loop distribution functions are considered. We obtain constraints on the dimensionless string tension parameter $G\mu<10^{-11}\sim10^{-10}$, which is more stringent by two orders of magnitude than that obtained by the high-frequency LIGO-Virgo experiment for one model, and less stringent for the other. The results provide the chance to test the Grand unified theories, with the spontaneous symmetry breaking scale of $U(1)$ being two-to-three orders of magnitude below $10^{16}$ GeV. The pulsar timing array experiments are thus quite complementary to the LIGO-Virgo experiment in probing the cosmic strings and the underlying beyond standard model physics in the early Universe.

  • Ghost Panorama

    分类: 光学 >> 量子光学 提交时间: 2023-02-19

    摘要: Computational ghost imaging or single-pixel imaging enables the image formation of an unknown scene using a lens-free photodetector. In this Letter, we present a computational panoramic ghost imaging system that can achieve the full-color panorama using a single-pixel photodetector, where a convex mirror performs the optical transformation of the engineered Hadamard-based circular illumination pattern from unidirectionally to omnidirectionally. To our best knowledge, it is the first time to propose the concept of ghost panorama and realize preliminary experimentations. It is foreseeable that ghost panorama will have more advantages in imaging and detection in many extreme conditions (e.g., scattering/turbulence, cryogenic temperatures, and unconventional spectra), as well as broad application prospects in the positioning of fast-moving targets and situation awareness for autonomous vehicles.

  • Prospects for Constraining interacting dark energy cosmology with gravitational-wave bright sirens detected by future SKA-era pulsar timing arrays

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Pulsar timing arrays (PTAs) have the potential to detect Nanohertz gravitational waves (GWs) that are usually generated by the individual inspiraling supermassive black hole binaries (SMBHBs) in the galactic centers. The GW signals as cosmological standard sirens can provide the absolute cosmic distances, thereby can be used to constrain the cosmological parameters. In this paper, we analyze the ability of future SKA-era PTAs to detect the existing SMBHBs candidates assuming the root mean square of timing noise $\sigma_t=20\ {\rm ns}$, and use the simulated PTA data to constrain the interacting dark energy (IDE) models with energy transfer rate $Q = \beta H\rho_c$. We find that, the future SKA-era PTAs will play an important role in constraining the IDE cosmology. Using only the mock PTA data consisting of 100 pulsars, we obtain $\sigma(H_0)=0.239\ {\rm km} \ {\rm s}^{-1} {\rm Mpc}^{-1}$ and $\sigma(\Omega_m)=0.0103$ in the I$\Lambda$CDM model, which are much better than the results from the Planck TT, TE, EE+lowE. However, the PTA data cannot provide a tight constraint on the coupling parameter $\beta$ compared with Planck, but the data combination of Planck+PTA can provide a rather tight constraint, i.e., $\sigma(\beta)=0.00232$, since the PTA data could break the parameter degeneracies inherent in CMB. In the I$w$CDM model, we obtain $\sigma(\beta)=0.00137$ and $\sigma(w)=0.0492$ from the Planck+PTA data combination. In addition, we also find that with the increase of the number of pulsars in PTA, the constraint results from the Planck+PTA will be further improved to some extent. We show that the observations of Nanohertz GWs with future SKA-era PTAs will provide a powerful tool for exploring the nature of dark energy and measuring the coupling between dark energy and dark matter.

  • Evolution of the post merger remnants from the coalescence of oxygen-neon and carbon-oxygen white dwarf pairs

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Although multidimensional simulations have investigated the processes of double WD mergers, post-merger evolution only focused on the carbon-oxygen (CO) WD or helium (He) WD merger remnants. In this work, we investigate for the first time the evolution of the remnants stemmed from the merger of oxygen-neon (ONe) WDs with CO WDs. Our simulation results indicate that the merger remnants can evolve to hydrogen- and helium-deficient giants with maximum radius of about 300Rsun. Our models show evidence that merger remnants more massive than 1.95Msun can ignite Ne before significant mass-loss ensues, and they thus would become electron-capture supernovae (ECSNe). However, remnants with initial masses less than 1.90Msun will experience further core contraction and longer evolutionary time before reaching at the conditions for Ne-burning. Therefore their fates are more dependent on mass-loss rates due to stellar winds, and thus more uncertain. Relatively high mass-loss rates would cause such remnants to end their lives as ONe WDs. Our evolutionary models can naturally explain the observational properties of the double WD merger remnant IRAS 00500+6713 (J005311). As previously suggested in the literature, we propose and justify that J005311 may be the remnant from the coalescence of an ONe WD and an CO WD. We deduce that the final outcome of J005311 would be a massive ONe WD rather than a supernova explosion. Our investigations may be able to provide possible constraints on the wind mass-loss properties of the giants which have CO-dominant envelopes.

  • The fractions of post-binary-interaction stars and evolved blue straggler stars on the red giant branch of globular clusters

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: The red giant branch (RGB) of globular clusters (GCs) is home to some exotic stars, which may provide clues on the formation of multiple stellar populations in GCs. It is well known that binary interactions are responsible for many exotic stars. Thus, it is important to understand what fraction of stars on the RGB of GCs is the result of binary interactions. In this paper, we performed a binary population synthesis study to track the number of post-binary-interaction (post-BI) stars that appear on the RGB, with particular emphasis on the evolved blue straggler stars (E-BSSs). Assuming an initial binary fraction of nearly 50%, we find that about half of the objects on the RGB (called giants) underwent the binary interactions, and that E-BSSs account for around 10% of the giants in our standard simulation. We also compare the properties of post-BI giants that evolved from different channels. We find that the initial orbital period and mass ratio distributions significantly affect the fraction of post-BI giants. Our results imply that the non-standard stars from binary interactions provide a non-negligible contribution to the RGB stars in GCs, which should be considered in future investigations of the origin of multiple stellar populations.

  • Evolution of the post merger remnants from the coalescence of oxygen-neon and carbon-oxygen white dwarf pairs

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Although multidimensional simulations have investigated the processes of double WD mergers, post-merger evolution only focused on the carbon-oxygen (CO) WD or helium (He) WD merger remnants. In this work, we investigate for the first time the evolution of the remnants stemmed from the merger of oxygen-neon (ONe) WDs with CO WDs. Our simulation results indicate that the merger remnants can evolve to hydrogen- and helium-deficient giants with maximum radius of about 300Rsun. Our models show evidence that merger remnants more massive than 1.95Msun can ignite Ne before significant mass-loss ensues, and they thus would become electron-capture supernovae (ECSNe). However, remnants with initial masses less than 1.90Msun will experience further core contraction and longer evolutionary time before reaching at the conditions for Ne-burning. Therefore their fates are more dependent on mass-loss rates due to stellar winds, and thus more uncertain. Relatively high mass-loss rates would cause such remnants to end their lives as ONe WDs. Our evolutionary models can naturally explain the observational properties of the double WD merger remnant IRAS 00500+6713 (J005311). As previously suggested in the literature, we propose and justify that J005311 may be the remnant from the coalescence of an ONe WD and an CO WD. We deduce that the final outcome of J005311 would be a massive ONe WD rather than a supernova explosion. Our investigations may be able to provide possible constraints on the wind mass-loss properties of the giants which have CO-dominant envelopes.

  • The effective field theory approach to strong coupling problem in $f(T)$ and $f(T,B)$ gravity

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We investigate the scalar perturbations and the possible strong coupling issues of $f(T)$ and $f(T,B)$ gravity around a cosmological background, applying the effective field theory (EFT) approach in a systematic way. We revisit the generalized EFT framework of modified teleparallel gravity, and we apply it by considering both linear and second-order perturbations for both theories. In the case of $f(T)$ gravity we find that no new scalar mode is present in both linear and second order perturbations, which suggests a strong coupling problem. However, based on the ratio of cubic to quadratic Lagrangians, we provide a simple estimation of the strong coupling scale, a result which shows that the strong coupling problem can be avoided at least for some modes. Additionally, in the case of $f(T,B)$ gravity we find that in general the extra scalar mode vanishes at quadratic order, but it becomes dynamical at higher orders, which implies that a strong coupling issue may appear, however estimating the strong coupling scale could provide a way to avoid it. Furthermore, we show that there are special subclasses of $f(T,B)$ gravity, including $f(R)$ case, which possess an extra propagating mode at linear perturbation level and thus are immediately free from strong coupling. In conclusion, perturbation behaviors that at first appear problematic may not inevitably lead to a strong coupling problem, as long as the relevant scale is comparable with the cutoff scale $M$ of the applicability of the theory.

  • Wafer-level substrate-free low-stress silicon nitride platform for THz metadevices and monolithically integrated narrowband metamaterial absorbers

    分类: 光学 >> 量子光学 提交时间: 2023-02-19

    摘要: The implementation of terahertz (THz) wafer-level metadevices is critical to advance the science for applications including (I) integrated focal plane array which can image for biology and (II) integrated narrowband absorbers for high spectral resolution THz spectroscopy. Substantial progress has been made in the development of THz metamaterials; however, a wafer-level low-stress THz metadevices platform remains a challenge. This paper experimentally demonstrates a substrate-free THz metadevices platform adopting engineered Si-rich and low-stress silicon nitride (SiNx) thin films, achieving an extensive THz transparency up to f = 2.5 THz. A new analytical model is first reported from the Lorentz model that can accurately predict spectral responses of metal insulator metal (MIM) metamaterial absorbers. The model is experimentally validated in the THz range and exploited for the first demonstration of a THz absorber, which exhibits performance approaching the predicted results. Our results show that the wafer-level SiNx platform will accelerate the development of large-scale, sophisticated substrate-free THz metadevices. The Lorentz model and its quadratic model will be a very practical method for designing THz metadevices.

  • The effective field theory approach to strong coupling problem in $f(T)$ and $f(T,B)$ gravity

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We investigate the scalar perturbations and the possible strong coupling issues of $f(T)$ and $f(T,B)$ gravity around a cosmological background, applying the effective field theory (EFT) approach in a systematic way. We revisit the generalized EFT framework of modified teleparallel gravity, and we apply it by considering both linear and second-order perturbations for both theories. In the case of $f(T)$ gravity we find that no new scalar mode is present in both linear and second order perturbations, which suggests a strong coupling problem. However, based on the ratio of cubic to quadratic Lagrangians, we provide a simple estimation of the strong coupling scale, a result which shows that the strong coupling problem can be avoided at least for some modes. Additionally, in the case of $f(T,B)$ gravity we find that in general the extra scalar mode vanishes at quadratic order, but it becomes dynamical at higher orders, which implies that a strong coupling issue may appear, however estimating the strong coupling scale could provide a way to avoid it. Furthermore, we show that there are special subclasses of $f(T,B)$ gravity, including $f(R)$ case, which possess an extra propagating mode at linear perturbation level and thus are immediately free from strong coupling. In conclusion, perturbation behaviors that at first appear problematic may not inevitably lead to a strong coupling problem, as long as the relevant scale is comparable with the cutoff scale $M$ of the applicability of the theory.

  • Ultra-compact X-ray binaries with He star companions

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Ultra-compact X-ray binaries (UCXBs) are low-mass X-ray binaries with hydrogen-deficient mass-donors and ultra-short orbital periods. They have been suggested to be the potential Laser Interferometer Space Antenna (LISA) sources in the low-frequency region. Several channels for the formation of UCXBs have been proposed so far. In this article, we carried out a systematic study on the He star donor channel, in which a neutron star (NS) accretes matter from a He main-sequence star through Roche-lobe overflow, where the mass-transfer is driven by gravitational wave radiation. Firstly, we followed the long-term evolution of the NS+He main-sequence star binaries by employing the stellar evolution code Modules for Experiments in Stellar Astrophysics, and thereby obtained the initial parameter spaces for the production of UCXBs. We then used these results to perform a detailed binary population synthesis approach to obtain the Galactic rates of UCXBs through this channel. We estimate the Galactic rates of UCXBs appearing as LISA sources to be $\sim3.1-11.9\, \rm Myr^{-1}$ through this channel, and the number of such UCXB-LISA sources in the Galaxy can reach about $1-26$ calibrated by observations. The present work indicates that the He star donor channel may contribute significantly to the Galactic UCXB formation rate. We found that the evolutionary tracks of UCXBs through this channel can account for the location of the five transient sources with relatively long orbital periods quite well. We also found that such UCXBs can be identified by their locations in the mass-transfer rate versus the orbital period diagram.

  • Cosmological model-independent measurement of cosmic curvature using distance sum rule with the help of gravitational waves

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Although the cosmic curvature has been tightly constrained in the standard cosmological model using observations of cosmic microwave background anisotropies, it is still of great importance to independently measure this key parameter using only late-universe observations in a cosmological model-independent way. The distance sum rule in strong gravitational lensing (SGL) provides such a way, provided that the three distances in the sum rule can be calibrated by other observations. In this paper, we propose that gravitational waves (GWs) can be used to provide the distance calibration in the SGL method, which can avoid the dependence on distance ladder and cover a wider redshift range. Using the simulated GW standard siren observation by the Einstein Telescope as an example, we show that this scheme is feasible and advantageous. We find that $\Delta\Omega_k\simeq 0.17$ with the current SGL data, which is slightly more precise than the case of using SN to calibrate. Furthermore, we consider the forthcoming LSST survey that is expected to observe many SGL systems, and we find that about $10^4$ SGL data could provide the precise measurement of $\Delta\Omega_k\simeq 10^{-2}$ with the help of GWs. In addition, our results confirm that this method of constraining $\Omega_k$ is strongly dependent on lens models. However, obtaining a more accurate phenomenological model for lens galaxies is highly predictable as future massive surveys observe more and more SGL samples, which will significantly improve the constraint of cosmic curvature.

  • Type Ia supernovae in NS+He star systems and the isolated mildly recycled pulsars

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Type Ia supernovae (SNe Ia) are successful cosmological distance indicators and important element factories in the chemical evolution of galaxies. They are generally thought to originate from thermonuclear explosions of carbon-oxygen white dwarfs in close binaries. However, the observed diversity among SNe Ia implies that they have different progenitor models. In this article, we performed the long-term evolution of NS+He star binaries with different initial He star masses ($M_{\rm He}^{\rm i}$) and orbital periods ($P_{\rm orb}^{\rm i}$) for the first time, in which the He star companions can explode as SNe Ia eventually. Our simulations indicate that after the He stars develop highly degenerate oxygen-neon (ONe) cores with masses near the Chandrasekhar limit, explosive oxygen burning can be triggered due to the ignition of central residual carbon. According to these calculations, we obtained an initial parameter space for the production of SNe Ia in the $\rm log\,$$P^{\rm i}_{\rm orb}-M^{\rm i}_{\rm He}$ plane. Meanwhile, we found that isolated mildly recycled pulsars can be formed after He stars explode as SNe Ia in NS+He star binaries, in which the isolated pulsars have minimum spin periods ($P_{\rm spin}^{\rm min}$) of $\sim 30-110\rm\,ms$ and final orbital velocities of $\sim \rm 60-360\,km\,s^{-1}$, corresponding to initial orbital periods of $0.07-10\rm\,d$. Our work suggests that the NS+He star channel may contribute to the formation of isolated mildly recycled pulsars with velocity $\rm \lesssim 360\,km\,s^{-1}$ in observations, and such isolated pulsars should locate in the region of pulsars with massive WD companions in the $P_{\rm spin}-\dot P_{\rm spin}$ diagram.

  • Cosmological model-independent measurement of cosmic curvature using distance sum rule with the help of gravitational waves

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Although the cosmic curvature has been tightly constrained in the standard cosmological model using observations of cosmic microwave background anisotropies, it is still of great importance to independently measure this key parameter using only late-universe observations in a cosmological model-independent way. The distance sum rule in strong gravitational lensing (SGL) provides such a way, provided that the three distances in the sum rule can be calibrated by other observations. In this paper, we propose that gravitational waves (GWs) can be used to provide the distance calibration in the SGL method, which can avoid the dependence on distance ladder and cover a wider redshift range. Using the simulated GW standard siren observation by the Einstein Telescope as an example, we show that this scheme is feasible and advantageous. We find that $\Delta\Omega_k\simeq 0.17$ with the current SGL data, which is slightly more precise than the case of using SN to calibrate. Furthermore, we consider the forthcoming LSST survey that is expected to observe many SGL systems, and we find that about $10^4$ SGL data could provide the precise measurement of $\Delta\Omega_k\simeq 10^{-2}$ with the help of GWs. In addition, our results confirm that this method of constraining $\Omega_k$ is strongly dependent on lens models. However, obtaining a more accurate phenomenological model for lens galaxies is highly predictable as future massive surveys observe more and more SGL samples, which will significantly improve the constraint of cosmic curvature.

  • Type Ia supernovae in NS+He star systems and the isolated mildly recycled pulsars

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Type Ia supernovae (SNe Ia) are successful cosmological distance indicators and important element factories in the chemical evolution of galaxies. They are generally thought to originate from thermonuclear explosions of carbon-oxygen white dwarfs in close binaries. However, the observed diversity among SNe Ia implies that they have different progenitor models. In this article, we performed the long-term evolution of NS+He star binaries with different initial He star masses ($M_{\rm He}^{\rm i}$) and orbital periods ($P_{\rm orb}^{\rm i}$) for the first time, in which the He star companions can explode as SNe Ia eventually. Our simulations indicate that after the He stars develop highly degenerate oxygen-neon (ONe) cores with masses near the Chandrasekhar limit, explosive oxygen burning can be triggered due to the ignition of central residual carbon. According to these calculations, we obtained an initial parameter space for the production of SNe Ia in the $\rm log\,$$P^{\rm i}_{\rm orb}-M^{\rm i}_{\rm He}$ plane. Meanwhile, we found that isolated mildly recycled pulsars can be formed after He stars explode as SNe Ia in NS+He star binaries, in which the isolated pulsars have minimum spin periods ($P_{\rm spin}^{\rm min}$) of $\sim 30-110\rm\,ms$ and final orbital velocities of $\sim \rm 60-360\,km\,s^{-1}$, corresponding to initial orbital periods of $0.07-10\rm\,d$. Our work suggests that the NS+He star channel may contribute to the formation of isolated mildly recycled pulsars with velocity $\rm \lesssim 360\,km\,s^{-1}$ in observations, and such isolated pulsars should locate in the region of pulsars with massive WD companions in the $P_{\rm spin}-\dot P_{\rm spin}$ diagram.