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Fundamental Parameters of a Binary System Consisting of a Red Dwarf and a Compact Star

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arXiv 2024年

作者： Ding, Xu Ji, KaiFan Song, ZhiMing Liu, NianPing Xiong, JianPing Cheng, Qiyuan Wang, ChuanJun Wang, JinLiang Wang, DeQing He, ShouSheng P.O. Box 110 Kunming650216 China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences P. O. Box 110 Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China University of the Chinese Academy of Sciences Yuquan Road 19# Shijingshan Block Beijing100049 China School of Information Yunnan University of Finance and Economics Kunming China Yunnan Key Laboratory of Service Computing Kunming China

TIC 157365951 has been classified as a δ Scuti type by the International Variable Star Index (VSX). Through the spectra from Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and its light curve, we further discovered that it is a binary system. This binary system comprises a red dwarf star and a compact star. Through the spectral energy distribution (SED) fitting, we determined the mass of the red dwarf star as M1 = 0.31 ± 0.01M☉ and its radius as R1 = 0.414 ± 0.004R☉. By fitting the double-peaked Hα emission, we derived the mass ratio of q = 1.76 ± 0.04, indicating a compact star mass of M2 = 0.54 ±0.01M☉. Using Phoebe to model the light curve and radial velocity curve for the detached binary system, we obtained a red dwarf star mass of M1 = 0.29 ± 0.02M☉, a radius of R1 = 0.39 ± 0.04R☉, and a Roche-lobe filling factor of f = 0.995 ± 0.129, which is close to the f = 1 expected for a semi-detached system. The Phoebe model gives a compact star mass M2 = 0.53 ± 0.05M☉. Constraining the system to be semidetached gives M1 = 0.34 ± 0.02M☉, R1 = 0.41 ± 0.01R☉, and M2 = 0.62 ± 0.03M☉. The consistency of the models is encouraging. The value of the Roche-lobe filling factor suggests that there might be ongoing mass transfer. The compact star mass is as massive as a typical white dwarf. © 2024, CC BY.

关键词： White dwarfs

An initial analysis of a strongly-lensed QSOs candidate identified by LAMOST

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arXiv 2023年

作者： Chen, Yanhui H. Tang, M.Y. Shu, H. Tu, H. Institute of Astrophysics Chuxiong Normal University Chuxiong675000 China School of Physics and Electronical Science Chuxiong Normal University Chuxiong675000 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences P.O. Box 110 Kunming650011 China Department of Astronomy Yunnan University Key Laboratory of Astroparticle Physics of Yunnan Province Kunming650091 China Physics Department Shanghai Key Lab for Astrophysics Shanghai Normal University Shanghai200234 China

From 2011 to 2021, LAMOST has released a total of 76,167 quasar data. We try to search for gravitationally lensed QSOs by limiting coordinate differences and redshift differences of these QSOs. The name, brightness, spectrum, photometry and other information of each QSO will be visually checked carefully. Special attention should be paid to check whether there are groups of galaxies, gravitationally lensed arcs, Einstein crosses, or Einstein rings near the QSOs. Through careful selection, we select LAMOST J160603.01+290050.8 (A) and LAMOST J160602.81+290048.7 (B) as a candidate and perform an initial analysis. The component A and B are 3.36 arc seconds apart and they display blue during photometric observations. The redshift values of component A and B are 0.2% different, their Gaia g values are 1.3% different, and their ugriz values are 1.0% or less different. For the spectra covering from 3,690 Å to 9,100 Å, the emission lines of C II, Mg, H γ, O III, and H β are present for both component A and B and the ratio of flux(B) to flux(A) from LAMOST is basically a constant, around 2.2. However, no galaxies have been found between component A and B. Inada et al. identified them as binary quasars. But we accidentally find a galaxy group near the component A and B. If the center of dark matter in the galaxy group is at the center between component A and B, the component A and B are probably gravitationally lensed QSOs. We estimate that the Einstein mass is 1.46 × 1011 M and the total mass of the lens is 1.34 × 1013 M. The deflection angle is 1.97 arc seconds at positions A and B and the velocity dispersion is 261 km s−1. Theoretically, this candidate could be a pair of fold images of a strong lensing system by a galaxy group, and we will investigate the possibility when the redshifts of nearby galaxies are available. Copyright © 2023, The Authors. All rights reserved.

关键词： Galaxies

The formation of blue large-amplitude pulsators from white-dwarf main-sequence star mergers

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arXiv 2023年

作者： Zhang, Xianfei Jeffery, C. Simon Su, Jie Bi, Shaolan Institute for Frontier in Astronomy and Astrophysics Beijing Normal University Beijing102206 China Department of Astronomy Beijing Normal University Beijing100875 China Armagh Observatory and Planetarium College Hill ArmaghBT61 9DG United Kingdom Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China

Blue large-amplitude pulsators (BLAPs) are hot low-mass stars which show large-amplitude light variations likely due to radial oscillations driven by iron-group opacities. Period changes provide evidence of both secular contraction and expansion amongst the class. Various formation histories have been proposed, but none are completely satisfactory. Zhang et al. (2017) proposed that the merger of a helium core white dwarf with a low-mass main-sequence star (HeWD+MS) can lead to the formation of some classes of hot subdwarf. We have analyzed these HeWD+MS merger models in more detail. Between helium-shell ignition and full helium-core burning, the models pass through the volume of luminosity – gravity– temperature space occupied by BLAPs. Periods of expansion and contraction associated with helium-shell flashes can account for the observed rates of period change. We argue that the HeWD+MS merger model provides at least one BLAP formation channel. © 2023, CC BY.

关键词： Helium

The growth history of local M 33-mass bulgeless spiral galaxies

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arXiv 2023年

作者： Kang, Xiaoyu Kudritzki, Rolf-Peter Zhang, Fenghui Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China LMU München Universitätssternwarte Scheinerstr. 1 München81679 Germany Institute for Astronomy University of Hawaii 2680 Woodlawn Drive HonoluluHI96822 United States

NGC 7793, NGC 300, M33 and NGC 2403 are four nearby undisturbed and bulgeless low-mass spiral galaxies with similar morphology and stellar mass. They are ideal laboratories to study disc formation scenarios and stellar mass growth histories. We construct a simple chemical evolution model by assuming that discs grow gradually with continuous metal-free gas infall and metal-enriched gas outflow. By means of the classical χ2 methodology, applied to the model predictions, the best combination of free parameters capable of reproducing the corresponding present-day observations is determined, i.e. the radial dependence of the infall timescale τ = 0.1r/Rd + 3.4 Gyr (Rd is the disc scale-length) and the gas outflow efficiency bout = 0.2. The model results are in excellent agreement with the general predictions of the inside-out growth scenario for the evolution of spiral galaxies. About 80% of the stellar mass of NGC 7793 is assembled within the last 8 Gyr and 40% within the last 4 Gyr. By comparing the best-fitting model results of the three other galaxies we obtain similar results, 72% (NGC 300), 66% (NGC 2403) and 79% (M33) stellar mass were assembled within the past ∼ 8 Gyr (i.e. z = 1). These four disc galaxies simultaneously increase their sizes and stellar masses as time goes by and they grow in size at ∼ 0.30 times the rate at which they grow in mass. The scale-lengths of these four discs are now 20% – 25% larger than at z = 1. Our best-fitting model predicted the stellar mass-metallicity relation and the metallicity gradients, constrained by the observed metallicities from HII-regions emission line analysis, agree well with the observations measured from individual massive red and blue supergiant stars and population synthesis of SDSS galaxies. Copyright © 2023, The Authors. All rights reserved.

关键词： Galaxies

Exploring the convective core of the high-amplitude δ Scuti star TIC 120857354 with asteroseismology

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arXiv 2024年

作者： Chen, Xinghao Zhang, Xiaobin Li, Yan Yunnan Observatories Chinese Academy of Sciences P.O. Box 110 Kunming650216 China Key Laboratory for Structure and Evolution of Celestial Objects Chinese Academy of Sciences P.O. Box 110 Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing100012 China University of Chinese Academy of Sciences Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China

Based on 2-minute cadence TESS data, 20 confident independent frequencies were identified for the star TIC 120857354. The Kolmogorov-Smirnov test reveals a rotational splitting of 2.40 μHz and a uniform frequency spacing of 74.6 μHz. Subsequently, five sets of rotational splittings were discerned, including a quintuplet and four pairs of doublets, aligning with the characteristics of p-mode rotational splitting. Based on the sets of rotational splittings and the uniform frequency spacing, we finally identified 4 radial modes, 6 dipole modes, and 10 quadrupole modes. Furthermore, we found that the frequency separations within the = 2 sequences show a decreasing trend towards lower-order modes, analogous to the = 0 sequences. A grid of theoretical models were computed to match the identified frequencies, revealing that TIC 120857354 is a main-sequence star with M = 1.54 ± 0.04 M☉, Z = 0.015 ± 0.003, Teff = 7441 ± 370 K, log g = 4.27 ± 0.01, R = 1.52 ± 0.01 R☉, L = 6.33 ± 1.53 L☉, age = 0.53 ± 0.07 Gyr, and Xc/X0 = 0.84 ± 0.05. In-depth analyses suggest that = 2 may be p-dominated mixed modes with pronounced g-mode characteristics, enabling us to probe deeper into interiors of the star and determine the relative size of the convective core to be Rc/R = 0.092 ± 0.002. Copyright © 2024, The Authors. All rights reserved.

关键词： Stars

MHD simulations of inward shocks in Cassiopeia A

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Research in Astronomy and Astrophysics 2020年第4期20卷 39-43页

作者： Chu-Yuan Yang Bi-Wen Bao Si-Ming Liu Yunnan Observatories Chinese Academy of SciencesKunming 650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing 100101China Department of Astronomy Key Laboratory of Astroparticle Physics of Yunnan ProvinceYunnan UniversityKunming 650091China Key Laboratory of Dark Matter and Space Astronomy Purple Mountain ObservatoryChinese Academy of SciencesNanjing 210033China

Cassiopeia A,the brightest radio supernova remnant(SNR)in the sky,has several unique characteristics in comparison to its *** its radio brightness and prominent soft-concave radio spectrum,itsγ-ray spectrum appears to have a low-energy cutoff near 2 GeV,and it is the only SNR with prominent hard X-ray *** the unusual radio properties may be attributed to strong emission from reverse shocks,the hard X-ray emission has been associated with high-speed inward shocks induced by high density ***,the low-energyγ-ray spectral cutoff could be attributed to slow penetration of lower energy particles accelerated near the inward shocks into high-density emission *** this paper,we carry out magneto-hydrodynamic(MHD)simulations of shocks in Cassiopeia A and demonstrate that its inward shock structure can indeed be reproduced via shock interactions with clumps of gases with a density of 20 cm-3.

关键词： acceleration of particles supernovae:individual(Cassiopeia A) ISM:supernova remnants X-rays:ISM

Investigation into the reflection properties of the neutron star low-mass X-ray binary 4U 1636−53

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arXiv 2023年

作者： Lyu, Ming Zhang, Guobao Wang, H.G. García, Federico Department of Physics Xiangtan University Hunan Xiangtan411105 China Key Laboratory of Stars and Interstellar Medium Xiangtan University Hunan Xiangtan411105 China Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650216 China Department of Astronomy School of Physics and Materials Science Guangzhou University Guangzhou510006 China Instituto Argentino de Radioastronomía CCT La Plata CONICET CICPBA UNLP C.C.5 Villa Elisa Buenos Aires1894 Argentina

We present the spectroscopy of the neutron star low-mass X-ray binary 4U 1636-53 using six simultaneous XMM-Newton and Rossi X-ray Timing Explorer observations. We applied different self-consistent reflection models to explore the features when the disk is illuminated by either the corona or the neutron star surface. We found that the spectra could be well fitted by these two types of models, with the derived emissivity index below a typical value of 3. The relative low emissivity can be explained if the neutron star and the corona, working together as an extended illuminator, simultaneously illuminate and ionize the disk. Additionally, the derived ionization parameter in the lamppost geometry is larger than the theoretical prediction. This inconsistency likely suggests that the corona does not emit isotropically in a realistic context. Furthermore, we also found that there is a possible trend between the height of the corona and the normalization of the disk emission. This could be understood either as a variation in the reflected radiation pressure or in the context of a jet base. Finally, we found that the disk is less ionized if it is illuminated by the neutron star, indicating that the illuminating source has significant influence on the physical properties of the disk. Copyright © 2023, The Authors. All rights reserved.

关键词： Stars

Precision Determination of Scintillation Screen Parameters from Annual Modulation Measurement of Pulsar Scintillation Arc Curvature with the FAST Telescope

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arXiv 2025年

作者： Huang, Yuanshang Shi, Xun Yao, Jumei Zhu, Weiwei Xu, Yonghua Yunnan University Kunming650500 China Xinjiang Astronomical Observatory Chinese Academy of Sciences 150 Science 1-Street Xinjiang Urumqi830011 China Key Laboratory of radio Astronomy Chinese Academy of Sciences Xinjiang Urumqi830011 China Xinjiang Key Laboratory of radio Astrophysics 150 Science1-Street Xinjiang Urumqi830011 China National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China Institute for Frontiers in Astronomy and Astrophysics Beijing Normal University Beijing102206 China Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China

Pulsar scintillation observations have revealed ubiquitous discrete scintillation screens in the interstellar medium. A major obstacle in identifying the nature of these screens is the uncertainty in their distances, which prevents precise correlation with known structures in the Milky Way. We used the Five-hundred-meter Aperture Spherical radio Telescope (FAST) to observe PSR B1237+25, PSR 1842+14, and PSR 2021+51. We detected 10 scintillation arcs in PSR B1237+25, 1 in PSR 1842+14, and at least 6 in PSR 2021+51. By modeling the annual modulation of these scintillation arcs, we constrained the distances of the scintillation screens, as well as the anisotropic scattering directions and the projected velocities in those directions. The scintillation screens are distributed throughout the entire paths between Earth and the pulsars. Among these, the distance to the main scintillation screen toward PSR B1237+25 is 267+32−28 pc, the scintillation screen toward PSR B1842+14 is at a distance of 240+210−120 pc, and the main scintillation screen toward PSR B2021+51 is located at 887+167−132 pc. Several screens in our sample appear at distances coinciding with the Local Bubble boundary, particularly the brightest scintillation arc toward PSR B1237+25. We provide a substantial sample of scintillation screen measurements, revealing the rich plasma density fluctuation structures present in the Milky Way. Copyright © 2025, The Authors. All rights reserved.

关键词： Pulsars

Transient phenomena from gas-erupting neutron stars

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arXiv 2021年

作者： Li, Huiquan Wang, Jiancheng Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China

Starquakes probably occur in rapidly spinning or ultra high field neutron stars. In this article, we argue that highly compressed gas containing electron-positron pairs could evaporate and erupt from inside the neutron star when a crack forms and then heals during a starquake. Under the influence of the existing oscillation modes of the star, the crack may have sufficiently large size and long lifetime. An appropriate amount of gas can erupt into the magnetosphere with relativistic and nearly uniform velocity, producing various transient and bursting phenomena. © 2021, CC0.

关键词： Stars