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arXiv 2024年

作者： Xiong, Jianping Li, Zhenwei Li, Jiao Zhang, Xiaobin Chen, Xiaodian Ji, Kaifan Han, Zhanwen Chen, Xuefei Yunnan Observatories Chinese Academy of Sciences 396 YangFangWang Guandu District 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 CAS Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China School of Astronomy and Space Science University of the Chinese Academy of Sciences Beijing101408 China Department of Astronomy China West Normal University Nanchong China

EL CVn-type systems represent a rare evolutionary stage in binary star evolution, providing ideal laboratories for investigating stable mass transfer processes and the formation of extremely low-mass white dwarfs (ELM WDs). The Transiting Exoplanet Survey Satellite (TESS) has delivered an extensive collection of high-precision time-domain photometric data, which is invaluable for studying EL CVn binaries. In this study, we identified 29 EL CVn systems from the TESS eclipsing binary catalogs (sectors 1–65), 11 of which are newly discovered. These systems consist of smaller, hotter pre-He white dwarfs and A/F main-sequence stars. The orbital periods of these binaries range from 0.64 to 2.5 days. Utilizing TESS light curves, Gaia distances, and multi-band photometric data (e.g., GALEX, 2MASS, WISE, SkyMapper), we modeled the light curves and spectral energy distributions to derive system parameters, including effective temperatures, masses, and radii. These systems were then compared with the white dwarf mass-period relation and the evolutionary tracks of ELM WDs. The comparison reveals that these binaries are consistent with the expected mass-period relation for white dwarfs and align well with the evolutionary tracks on the Teff -log g diagram for ELM WDs. This result suggests that these EL CVn systems likely formed through stable mass transfer processes. We provide a catalog of complete parameters for 29 EL CVn systems identified from the TESS survey. This catalog will serve as an essential resource for studying binary mass transfer, white dwarf formation, and pulsation phenomena in EL CVn-type systems. Copyright © 2024, The Authors. All rights reserved.

关键词： White dwarfs

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Photometric investigation on the W-subtype contact binary V1197 Her

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Research in Astronomy and Astrophysics 2020年第1期20卷 77-82页

作者： Xiao Zhou Boonrucksar Soonthomthum Yunnan Observatories Chinese Academy of SciencesKunming 650216China National Astronomical Research Institute of Thailand 260 Moo 4T.DonkaewA.MaerimChiangmai50180Thailand Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing 100101China

Multi-color light curves of V1197 Her were obtained with the 2.4 meter optical telescope at the Thai National Observatory and the Wilson-Devinney(W-D)program was used to model the observational light *** photometric solutions reveal that V1197 Her is a W-subtype shallow contact binary system with a mass ratio of q=2.61 and a fill-out factor of f=15.7%.The temperature difference between the primary star and secondary star is only 140 K in spite of the low degree of contact,which means that V1197 Her is not only in geometrical contact configuration but is also already under thermal contact *** orbital inclination of V1197 Her is as high as i=82.7?,and the primary star is completely eclipsed at the primary *** totally eclipsing characteristic implies that the determined physical parameters are highly *** masses,radii and luminosities of the primary star(star 1)and secondary star(star2)are estimated to be M1=0.30(1)M⊙,M2=0.77(2)M⊙,R1=0.54(1)R⊙,R2=0.83(1)R⊙,L1=0.18(1)L⊙and L2=0.38(1)L⊙.The evolutionary statuses of the two component stars are drawn in the Hertzsprung-Russell diagram,showing that the less massive but hotter primary star is more evolved than the secondary *** period of V1197 Her is decreasing continuously at a rate of d P/dt=-2.58×10^-7 day·year^-1,which can be explained by mass transfer from the more massive star to the less massive one at a rate of dM2/dt=-1.61×10^-7 M⊙year^-*** light curves of V1197 Her are reported to show the O’Connell ***,a cool spot is added to the more massive star to model the asymmetry in the light curves.

关键词： techniques:photometric binaries:eclipsing stars:fundamental parameters

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Nine New Cataclysmic Variable Stars with Negative Superhumps

arXiv

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arXiv 2023年

作者： Sun, Qi-Bin Qian, Sheng-Bang Zhu, Li-Ying Liao, Wen-Ping Zhao, Er-Gang Li, Fu-Xing Shi, Xiang-Dong Li, Min-Yu Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Department of Astronomy Key Laboratory of Astroparticle Physics of Yunnan Province Yunnan University Kunming650091 China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Yuquan Road Shijingshan District Beijing China

Negative superhumps (NSHs) are signals a few percent shorter than the orbital period of a binary star and are considered to originate from the reverse precession of the tilted disk. Based on TESS photometry, we find nine new cataclysmic variable stars (CVs) with NSHs. Three (ASAS J1420, TZ Per, and V392 Hya) of these stars similar to AH Her still have NSHs during dwarf nova outbursts, and the NSH amplitude varies with the outburst. The variation in the radius of the accretion disk partially explains this phenomenon. However, it does not explain the rebound of the NSH amplitude after the peak of the outburst and the fact that the NSH amplitude of the quiescence is sometimes not the largest, and it is necessary to combine the disk instability model (DIM) and add other ingredients. Therefore, we suggest that the variation of NSH amplitude with outburst can be an essential basis for studying the origin of NSHs and improving the DIM. The six (ASASSN-V J1137, ASASSN-V J0611, 2MASS J0715, LAMOST J0925, ASASSN-17qj, and ZTF18acakuxo) remaining stars have been poorly studied, and for the first time we determine their orbital periods, NSHs and Superorbital signal (SOR) periods. The NSH periods and amplitudes of ASASSN-V J1137 and ASASSN-17qj vary with the SOR, and based on the comparison of the observations with the theory, we suggest that a single change in tilted disk angle does not explain the observations of the SOR and that other ingredients need to be considered as well. Copyright © 2023, The Authors. All rights reserved.

关键词： Stars

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Searching for the highest energy of pulsation and critical luminosity of Swift J0243.6+6124 observed by Insight-HXMT

arXiv

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arXiv 2024年

作者： Zhao, Qing-Xia Hou, Xian Ge, Ming-Yu Zhang, Shuang-Nan Xiao, Yun-Xiang Tuo, You-Li Yang, Zi-Xu Kong, Ling-Da Qu, Jin-Lu Zhang, Shu Wang, Jian-Cheng Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing100049 China University of Chinese Academy of Sciences Chinese Academy of Sciences Beijing100049 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China Institut für Astronomie und Astrophysik Sand 1 TübingenD-72076 Germany School of Physics and Optoelectronic Engineering Shandong University of Technology Zibo255000 China

Owing to the broad energy coverage of Insight-HXMT in the hard X-ray band, we detected the highest energy of pulsation exceeding 200 keV around the 2017-2018 outburst peak of the first Galactic pulsating ultraluminous X-ray source (PULX) Swift J0243.6+6124, which is the highest energy detected from PULXs to date. We also obtained the highest energy of pulsation of every exposure during the outburst in 2017-2018, and found the highest energy is roughly positively correlated with luminosity. Using our newly developed method, we identified the critical luminosity being 4 × 1038 erg s-1 when the main peaks of the low and high energy pulse profiles became aligned, which separates the fan-beam dominated and pencil-beam dominated accretion regimes. Above the critical luminosity, the phase of the main peak shifted gradually from 0.5 to 0.8 until the outburst peak in all energy bands is reached, which is in agreement with the phase shift found previously at low energies. Our result is consistent with what is derived from spectral analysis. Copyright © 2024, The Authors. All rights reserved.

关键词： Luminance

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Radial velocity variability fractions of different types of hot subdwarf stars

arXiv

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arXiv 2024年

作者： He, Ruijie Meng, Xiangcun Lei, Zhenxin Yan, Huahui Lan, Shunyi Yunnan Observatories Chinese Academy of Sciences Kunming650011 China University of the Chinese Academy of Sciences Beijing100049 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 Key Laboratory of Stars and Interstellar Medium Xiangtan University Xiangtan411105 China Physics Department Xiangtan University Xiangtan411105 China Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment School of Space Science and Physics Shandong University at Weihai Weihai264209 China

Context. It is generally thought that hot subdwarfs are helium-core- or helium-shell-burning objects with extremely thin hydrogen envelopes and that binary interactions are always needed in their formation. Different types of hot subdwarfs may have different origins, which will cause them to present different radial velocity (RV) variability properties. Aims. We plan to study the RV-variability fractions of different types of hot subdwarfs, as well as their distributions in the Teff – log g diagram. This provides insights into the formation of hot subdwarfs. Methods. The cross-correlation function method was adopted to measure RV variations in 434 hot subdwarfs based on spectra obtained with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Light curves from the Transiting Exoplanet Survey were also used to search for short-period binary hot subdwarfs. Results. Only 6 ± 4% of our single-lined He-rich hot subdwarfs that only show spectroscopic features of hot subdwarfs are found to be RV variable, which is lower than the fraction of single-lined He-poor sdB stars (31 ± 3%). Single-lined sdB stars with effective temperatures (Teff) ∼ 25,000 – 33,000 K show an RV-variability fraction of 34 ± 5%, while lower RV-variability fractions are observed for single-lined sdB stars cooler than about 25,000 K (11 ± 4%), single-lined sdB/OB stars with Teff ∼ 33,000 – 40,000 K and surface gravities ∼ 5.7 – 6.0 (13 ± 3%), as well as single-lined sdO/B stars with Teff ∼ 45,000 – 70,000 K (10 ± 7%). Single-lined hot subdwarfs with Teff ∼ 35,000 – 45,000 K located above the extreme horizontal branch (EHB) show a similar RV-variability fraction of 34 ± 9% as single-lined sdB stars at about 25,000 – 33,000 K. The largest RV-variability fraction of 51 ± 8% is found in single-lined hot subdwarfs below the canonical EHB. The detected RV-variability fraction of our composite hot subdwarfs with an infrared excess in their spectral energy distributions is 9 ± 3%, which is

关键词： Exoplanets

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Stellar cycle and evolution of polar spots in an M+WD binary

arXiv

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arXiv 2024年

作者： Zhao, Xinlin Wang, Song Li, Xue Xiang, Yue Xu, Fukun Gu, Shenghong Liu, Jifeng Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China Yunnan Observatories Chinese Academy of Sciences Kunming650216 China School of Astronomy and Space Sciences University of Chinese Academy of Sciences Beijing100049 China Institute for Frontiers in Astronomy and Astrophysics Beijing Normal University Beijing102206 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China WHU-NAOC Joint Center for Astronomy Wuhan University Hubei Wuhan430072 China

Stellar activity cycles reveal continuous relaxation and induction of magnetic fields. The activity cycle is typically traced through the observation of cyclic variations in total brightness or Ca H&K emission flux of stars, as well as cyclic variations of orbital periods of binary systems. In this work, we report the identification of a semi-detached binary system (TIC 16320250) consisting of a white dwarf (0.67 M☉) and an active M dwarf (0.56 M☉). The long-term multi-band optical light curves spanning twenty years revealed three repeated patterns, suggestive of a possible activity cycle of about ten years of the M dwarf. Light curve fitting indicates the repeated variation is caused by the evolution, particularly the motion, of polar spots. The significant Ca H&K, Hα, ultra-violet, and X-ray emissions imply that the M dwarf is one of the most magnetically active stars. We propose that in the era of large time-domain photometric sky surveys (e.g., ASAS-SN, ZTF, LSST, Sitian), long-term light curve modeling can be a valuable tool for tracing and revealing stellar activity cycle, especially for stars in binary systems. Copyright © 2024, The Authors. All rights reserved.

关键词： White dwarfs

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TV Mon - post mass transfer Algol type binary with δ Scuti pulsations in primary component.

arXiv

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arXiv 2024年

作者： Kovalev, Mikhail Li, Zhenwei Xiong, Jianping Matekov, Azizbek Bo, Zhang Chen, Xuefei Han, Zhanwen Yunnan Observatories China Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China University of Chinese Academy of Sciences Yuquan Road 19 Sijingshang Block Beijing100049 China Ulugh Beg Astronomical Institute Uzbekistan Academy of Sciences 33 Astronomicheskaya str. Tashkent100052 Uzbekistan Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China

We present a study of the detached eclipsing binary TV Mon using spectra from the LAMOST medium-resolution survey and ASAS-SN, CoRoT photometry. We apply multiple-epochs spectral fitting to derive RV and spectral parameters. The analysis of eclipses in CoRoT data show the relative sizes of the stellar components and almost edge-on circular orbit. Combining the spectral and photometrical solutions we estimate masses and radii of the components: MA,B = 2.063 ± 0.033(stat.) ± 0.095(syst.), 0.218 ± 0.004(stat.) ± 0.018(syst.) M☉, RA,B = 2.394 ± 0.014, 2.860 ± 0.016 R☉. SED analysis and Gaia parallax allow us to get estimation of temperatures Teff A,B = 7624+−194174, 5184+−130123 K and distance d = 907 ± 11 pc. We identify three δ Scuti type pulsation frequencies in the primary component, while we also suspect TV Mon having a spot activity in the secondary component. This system experienced intensive mass transfer and mass ratio reversal in the past, but currently shows no signs of mass transfer in the spectra. The low mass component will lose its outer envelope and shrink to the helium white dwarf, the mass and orbital period of which are in good agreement with evolutionary models predictions. Copyright © 2024, The Authors. All rights reserved.

关键词： White dwarfs

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Probing the shape of the brown dwarf desert around main-sequence A-F-G-type stars using post-common-envelope WD−BD binaries

arXiv

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arXiv 2024年

作者： Chen, Zhangliang Chen, Yizhi Chen, Chen Ge, Hongwei Ma, Bo School of Physics and Astronomy Sun Yat-sen University Zhuhai519082 China CSST Science Center for the Guangdong-HongKong-Macau Great Bay Area Sun Yat-sen University Zhuhai519082 China Yunnan Observatories Chinese Academy of Sciences 396 YangFangWang Guandu District 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

Context. Brown dwarfs (BDs) with masses in the range 40−60 MJup are rare around solar-type main-sequence (MS) stars, which gives rise to the brown dwarf desert (BDD). One caveat associated with previous studies of BDD is the relatively limited sample size of MS−BD binaries with accurately determined BD masses. Aims. We aim to produce a large sample of BD companions with precisely determined masses around MS A-F-G-type stars using observations of post-common-envelope white dwarf (WD)−BD binaries. Methods. We employed the rapid binary evolution code COMPAS to deduce the properties of MS−BD binary progenitors from post-common-envelope WD−BD binaries. With this method, we increase the sample of directly observed MS−BD binaries, enriching the data available for analyzing the BDD around MS A-F-G-type stars. Results. Our study opens a new window for studying the shape of the BDD around A-F-G-type MS stars in the short-period regime. We find tentative evidence, albeit with a small sample size, that the "driest" part of the BDD around A-F-G-type stars may extend into an orbital period of several hundred days. More post-common-envelope WD−BD binaries detected in the future will advance our understanding of the BDD around A-F-G-type stars. © 2024, CC BY.

关键词： White dwarfs

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Physical properties of γ Doradus pulsating stars and their relationship with long-period δ Scuti variables

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Research in Astronomy and Astrophysics 2019年第1期19卷 1-20页

作者： Sheng-Bang Qian Lin-Jia Li Jia-Jia He Jia Zhang Li-Ying Zhu Zhong-Tao Han Yunnan Observatories Chinese Academy of Sciences Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Center for Astronomical Mega-Science Chinese Academy of Sciences University of Chinese Academy of Sciences

We present LAMOST data on 168 γ Doradus(γ Dor) pulsating stars including stellar atmospheric parameters of 137 variables and spectral types for all of the samples. The distributions of period(P), temperature(T), gravitational acceleration(log(g)) and metallicity [Fe/H] are shown. It is found that most γ Dor variables are main-sequence stars with early F spectral types and temperatures from 6880 K to7280 K. They are slightly more metal poor than the Sun with a metallicity range from-0.4 to 0. On the H-R and log g-T diagrams, both the γ Dor and δ Scuti(δ Sct) stars occupy in the same region and some are beyond the borders predicted by current stellar pulsation theories. It is discovered that the physical properties of γ Dor stars are similar to those of long-period δ Sct(P > 0.3 d) stars. The stellar atmospheric parameters are all correlated with the pulsation period for short-period δ Sct variables(P < 0.3 d), but there are no such relations for γ Dor or long-period δ Sct stars. These results reveal that γ Dor and long-period δ Sct are the same group of pulsating stars and they are different from short-period δ Sct variables. Meanwhile, 33γ Dor stars are identified as candidates of binary or multiple systems.

关键词： stars:fundamental parameters stars:oscillations stars:binaries:spectroscopic stars:variables:other

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More than two hundred and fifty thousand spectroscopic binary or variable star candidates discovered by LAMOST

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Research in Astronomy and Astrophysics 2019年第5期19卷 15-26页

作者： Sheng-Bang Qian Xiang-Dong Shi Li-Ying Zhu Lin-Jia Li Jia Zhang Er-Gang Zhao Zhong-Tao Han Xiao Zhou Xiao-Hui Fang Wen-Ping Liao Yunnan Observatories Chinese Academy of Sciences Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Center for Astronomical Mega-Science Chinese Academy of Sciences University of Chinese Academy of Sciences

About 786.4 thousand stars were observed by LAMOST twice or more during the first stage of its spectroscopic survey. The radial velocity differences for about 256 thousand targets are larger than10 km s^(-1) and they are possible spectroscopic binary or variable candidates(SBVCs). It is shown that most SBVCs are slightly metal poorer than the Sun. There are two peaks in the temperature distribution of SBVCs around 5760 K and 4870 K, while there are three peaks in the distribution of the gravitational acceleration at 2.461, 4.171 and 4.621 cm s^(-2). The locations of SBVCs on the [Fe/H]-T, [Fe/H]-log g, log g-T and H-R diagrams are investigated. It is found that the detected SBVCs could be classified into four groups. The first group has higher log g～4.621 and lower T ～ 4870 K which are mainly cool red dwarf binaries. The second group of SBVCs has logg around 4.171 cm s^(-2) that includes binaries and pulsating stars such as δSet and γ Dor variables. The gravitational accelerations of the third group of SBVCs are higher and some of them are below the zero-age main sequence. They may be contact binaries in which the primary components are losing energy to the secondaries in the common envelopes and are at a special stellar evolutionary *** last group is composed of giants or supergiants with log g around 2.461 cm s^(-2) that may be evolved pulsating stars. One target(C134624.29+333921.2) is confirmed as an eclipsing binary with a period of 0.65 days. A preliminary analysis suggests that it is a detached binary with a mass ratio of 0.46. The primary fills its critical Roche lobe by about 89%, indicating that mass transfer will occur between the two components.

关键词： stars fundamental parameters-stars binaries spectroscopic-stars:oscillations-stars:binaries eclipsing-stars variables other

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