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.
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.
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.
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.
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.
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.
点击量
待评议
点击量
下载量
评论
