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A flexible method for estimating luminosity functions via Kernel Density Estimation

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arXiv 2020年

作者： Yuan, Zunli Jarvis, Matt J. 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 Astrophysics University of Oxford Denys Wilkinson Building Keble Road OxfordOX1 3RH United Kingdom Physics and Astronomy Department University of the Western Cape Bellville7535 South Africa

We propose a flexible method for estimating luminosity functions (LFs) based on kernel density estimation (KDE), the most popular nonparametric density estimation approach developed in modern statistics, to overcome issues surrounding binning of LFs. One challenge in applying KDE to LFs is how to treat the boundary bias problem, since astronomical surveys usually obtain truncated samples predominantly due to the flux-density limits of surveys. We use two solutions, the transformation KDE method (t), and the transformation-reflection KDE method (tr) to reduce the boundary bias. We develop a new likelihood cross-validation criterion for selecting optimal bandwidths, based on which, the posterior probability distribution of bandwidth and transformation parameters for t and tr are derived within a Markov chain Monte Carlo (MCMC) sampling procedure. The simulation result shows that t and tr perform better than the traditional binned method, especially in the sparse data regime around the flux-limit of a survey or at the bright-end of the LF. To further improve the performance of our KDE methods, we develop the transformation-reflection adaptive KDE approach (tra). Monte Carlo simulations suggest that it has a good stability and reliability in performance, and is around an order of magnitude more accurate than using the binned method. By applying our adaptive KDE method to a quasar sample, we find that it achieves estimates comparable to the rigorous determination in a previous work, while making far fewer assumptions about the LF. The KDE method we develop has the advantages of both parametric and non-parametric methods. Copyright © 2020, The Authors. All rights reserved.

关键词： Surveys

SCATTER: A New Common Envelope Formalism

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arXiv 2022年

作者： Di Stefano, Rosanne Kruckow, Matthias U. Gao, Yan Neunteufel, Patrick G. Kobayashi, Chiaki Harvard-Smithsonian Center for Astrophysics 60 Garden St CambridgeMA02138 United States Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China Département d’Astronomie Université de Genève Chemin Pegasi 51 VersoixCH-1290 Switzerland Université de Genève GenevaCH-1211 Switzerland University of Chinese Academy of Sciences China Institute of Gravitational Wave Astronomy School of Physics and Astronomy University of Birmingham BirminghamB15 2TT United Kingdom Max Planck Institut für Astrophysik Karl-Schwarzschild-Straße 1 Garching bei München85748 Germany Centre for Astrophysics Research Department of Physics Astronomy and Mathematics University of Hertfordshire HatfieldAL10 9AB United Kingdom

One of the most mysterious astrophysical states is the common envelope (CE) phase of binary evolution, in which two stars are enshrouded by the envelope shed by one of them. Interactions between the stars and the envelope shrinks the orbit. The CE can lead to mergers or to a subsequent phase of interactions. Mergers may involve any combination of two compact objects and/or stars. Some involving white dwarfs, may produce Type Ia supernovae, while merging neutron stars may yield gamma-ray bursts, and merging compact objects of all kinds produce gravitational radiation. Since CEs can arise from a variety of different initial conditions, and due to the complexity of the processes involved, it is difficult to predict their end states. When many systems are being considered, as in population synthesis calculations, conservation principles are generally employed. Here we use angular momentum in a new way to derive a simple expression for the final orbital separation. This method provides advantages for the study of binaries and is particularly well-suited to higher order multiples, now considered to be important in the genesis of potential mergers. Here we focus on CEs in binaries, and the follow-up paper extends our formalism to multiple star systems within which a CE occurs. © 2022, CC0.

关键词： Merging

Searching for quasi-periodic modulations in γ-ray active galactic nuclei

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arXiv 2020年

作者： Zhang, Peng-Fei Yan, Da-Hai Zhou, Jia-Neng Wang, Jian-Cheng Zhang, Li Department of Astronomy School of Physics and Astronomy Key Laboratory of Astroparticle Physics of Yunnan Province Yunnan University Kunming650091 China Key Laboratory of Dark Matter and Space Astronomy Purple Mountain Observatory Chinese Academy of Sciences Nanjing210008 China Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Observatory Chinese Academy of Sciences Kunming650011 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Shanghai Astronomical Observatory Chinese Academy of Sciences 80 Nandan Road Shanghai200030 China

We perform a systematic search of quasi-periodic variabilities in γ-ray active galactic nuclei (AGNs) in the third Fermi Large Area Telescope source catalog (3FGL). We employe two techniques, Lomb-Scargle Periodogram (LSP) and Weighted Wavelet Z-transform (WWZ), to obtain power spectra of γ-ray light curves covering from 2008 August to 2016 December. The results show that besides several objects that have been reported in previous works, an additional source, the FSRQ PKS 0601-70 has a possible quasi-periodic variability of 450 days in its γ-ray light curves with the significance of > 3σ. The physical implications of our findings are discussed. Copyright © 2020, The Authors. All rights reserved.

关键词： Z transforms

First photometric study of ultrashort-period contact binary 1SWASP J140533.33＋114639.1

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Research in Astronomy and Astrophysics 2018年第3期18卷 57-62页

作者： Bin Zhang Sheng-Bang Qian Ri Michel Boonrucksar Soonthornthum Li-Ying Zhu Yunnan Observatories Chinese Academy of Sciences Kunming 650216 China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming 650216 China University of Chinese Academy of Sciences Beijing 100049 China Instituto de Astronomia UNAM Ensenada Mexico National Astronomical Research Institute of Thailand Chiang Mai 50200 Thailand

In this paper,CCD photometric light curves for the short-period eclipsing binary 1 SWASP J140533.33＋114639.1（hereafter J1405） in the BV R bands are presented and analyzed using the 2013 version of the Wilson-Devinney（W-D） code. It is discovered that J1405 is a W-subtype shallow contact binary with a contact degree of f = 7.9±0.5% and a mass ratio of q = 1.55±0.02. In order to explain the asymmetric light curves of the system,a cool starspot on the more massive component is employed. This shallow contact eclipsing binary may have been formed from a short-period detached system through orbital shrinkage due to angular momentum loss. Based on the（O-C） method,the variation of orbital period is studied using all the available times of minimum light. The（O-C） diagram reveals that the period is increasing continuously at a rate of d P/dt = ＋2.09×10^-7 d yr^-1,which can be explained by mass transfer from the less massive component to the more massive one.

关键词： stars binaries close - stars binaries eclipsing - stars individual （1SWASPJ140533.33＋114639.1）

KIC 10736223: An Algol-type eclipsing binary just undergone the rapid mass-transfer stage

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arXiv 2020年

作者： Chen, Xinghao Zhang, Xiaobin Li, Yan Chen, Hailiang Luo, Changqing Su, Jie Chen, Xuefei Han, Zhanwen 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 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

This paper reports the discovery of an Algol system KIC 10736223 that just past the rapid mass transfer stage. From the light curve and radial-velocity modelling we find KIC 10736223 to be a detached Algol system with the less-massive secondary nearly filling its Roche lobe. Based on the short-cadence Kepler data, we analyzed intrinsic oscillations of the pulsator and identified six secured independent δ Scuti-type pulsation modes (f1, f3, f9, f19, f42, and f48). We compute two grids of theoretical models to reproduce the δ Scuti freqiencies, and find fitting results of mass-accreting models meet well with those of single-star evolutionary models. The fundamental parameters of the primary star yielded with asteroseismology are M = 1.57+0.05/-0.09 M☉, Z = 0.009 ± 0.001, R = 1.484+0.016/-0.028 R☉, log g = 4.291+0.004/-0.009, Teff = 7748+230/-378 K, L = 7.136+1.014/-1.519 L☉. The asteroseismic parameters match well with the dynamical parameters derived from the binary model. Moreover, our asteroseismic results show that the pulsator is an almost unevolved star with an age between 9.46-11.65 Myr for single-star evolutionary models and 2.67-3.14 Myr for mass-accreting models. Thereofore, KIC 10736223 may be an Algol system that has just undergone the rapid mass-transfer process. Copyright © 2020, The Authors. All rights reserved.

关键词： Mass transfer

The accretion geometry of the asynchronous polar V1432 aql

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arXiv 2020年

作者： Qishan, Wang Shengbang, Qian Liying, Zhu 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 University of Chinese Academy of Sciences Yuquan Road 19# Sijingshang Block Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Science 20A Datun Road Chaoyang Distric Beijing100012 China

As the only eclipsing asynchronous polar (AP), V1432 Aql provides an excellent laboratory to study the interaction between the accreted matter and the magnetic field. However, due to its complex emission, a more physical understanding of its accretion geometry is still outstanding. Here, we report an X-ray spectral study using contemporaneous observations from NuSTAR and Swift. We detect significant Compton reflection and confirm earlier reports of a high soft X-ray temperature ∼ 52 keV. We suggest that the multi-temperature emission is due to a distribution of the specific accretion rate over the accretion region, which leads to a continuous temperature distribution over the heated area and explains the high temperature of the soft X-rays. We interpret these characteristics as the results of the inefficient accretion in APs. Thus the accretion stream can punch deeply into the magnetosphere and feed the white dwarf (WD) over a much narrower accretion region near its equator. Additionally, the broad-band X-rays provide details of the accretion;the low total accretion rate of ∼ 1×10−10 M yr−1 contradicts the speculation that V1432 Aql was a recent nova, while the high specific accretion rate of ∼ 5.6 g cm−2 s−1 explains the significant reflection from the surface of the WD. Copyright © 2020, The Authors. All rights reserved.

关键词： White dwarfs

The possible equation of state of dark matter in low surface brightness galaxies

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arXiv 2020年

作者： Gong, Xiaobo Tang, Meirong Xu, Zhaoyi Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang KunmingGuandu District650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China University of Chinese Academy of Sciences Beijing100049 China Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing100049 China

The observed rotation curves of low surface brightness (LSB) galaxies play an essential role in studying dark matter, and indicate that there exists a central constant density dark matter core. However, the cosmological N-body simulations of cold dark matter predict an inner cusped halo with a power-law mass density distribution, and can’t reproduce a central constant-density core. This phenomenon is called cusp-core problem. When dark matter is quiescent and satisfies the condition for hydrostatic equilibrium, using the equation of state can get the density profile in the static and spherically symmetric space-time. To solve the cusp-core problem, we assume that the equation of state is independent of the scaling transformation. Its lower order approximation for this type of equation of state can naturally lead to a special case, i.e. p = ζρ+2ǫVrot2 ρ, where p and ρ are the pressure and density, Vrot is the rotation velocity of galaxy, ζ and ǫ are positive constants. It can obtain a density profile that is similar to the pseudo-isothermal halo model when ǫ is around 0.15. To get a more widely used model, let the equation of state include the polytropic model, i.e. p = ρζs0 ρ1+s +2ǫVrot2 ρ, we can get other kinds of density profiles, such as the profile that is nearly same with the Burkert profile, where s and ρ0 are positive constants. Copyright © 2020, The Authors. All rights reserved.

关键词： Galaxies

Shell helium-burning hot subdwarf B stars as candidates for blue large-amplitude pulsators

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arXiv 2022年

作者： Xiong, H. Casagrande, L. Chen, X. Vos, J. Zhang, X. Justham, S. Li, J. Wu, T. Li, Y. Han, Z. Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China Research School of Astronomy and Astrophysics The Australian National University CanberraACT2611 Australia Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Astronomical Institute of the Czech Academy of Sciences OndřejovCZ-25165 Czech Republic Department of Astronomy Beijing Normal University Beijing100875 China School of Astronomy & Space Science University of the Chinese Academy of Sciences Beijing100012 China The Key Laboratory of Optical Astronomy National Astronomical Observatories The Chinese Academy of Sciences Datun Road Beijing100012 China University of Chinese of Academy of Science Yuquan Road 19 Shijingshan Block Beijing100049 China Anton Pannekoek Institute for Astronomy University of Amsterdam Science Park 904 Amsterdam1098XH Netherlands Max Planck Institute for Astrophysics Karl-Schwarzschild-Str. 1 Garching85748 Germany Institute of Theoretical Physics Shanxi University Taiyuan030006 China Key Laboratory of Space Astronomy and Technology National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China

Blue large-amplitude pulsators (BLAPs) are a newly discovered type of variable star. Their typical pulsation periods are on the order of a few tens of minutes, with relatively large amplitudes of 0.2-0.4 mag in optical bands, and their rates of period changes are on the order of 10-7yr-1(both positive and negative). They are extremely rare objects and attempts to explain their origins and internal structures have attracted a great deal of attention. Previous studies have proposed that BLAPs may be pre-white dwarfs, with masses around 0.3Mo, or core-helium-burning stars in the range of ∼ 0.7-1.1Mo. In this work, we use a number of MESA models to compute and explore whether BLAPs could be explained as shell helium-burning subdwarfs type B (SHeB sdBs). The models that best match existing observational constraints have helium core masses in the range of ∼ 0.45-0.5Mo. Our model predicts that the positive rate of period change may evolve to negative. The formation channels for SHeB sdBs involve binary evolution and although the vast majority of BLAPs do not appear to be binaries (with the exception of HD 133729), the observational constraints are still very poor. Motivated by these findings, we explored the Roche lobe overflow channel. Of the 304 binary evolution models we computed, about half of them are able to produce SHeB sdBs in long-period binaries that evade detection from the limited observations that are currently available. Copyright © 2022, The Authors. All rights reserved.

关键词： White dwarfs

Black hole magnetospheres in the born-infeld theory

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arXiv 2019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

We study the force-free electrodynamics on rotating black holes in the Born-Infeld (BI) effective theory. The stream equation describing a steady and axisymmetric magnetosphere is derived. From its near-horizon behavior, we obtain the modified Znajek regularity condition, with which we find that the horizon resistivity in the BI theory is generally not a constant. As expected, the outer boundary condition far away from the hole remains unchanged. In terms of the conditions at both boundaries, we derive the perturbative solution of split monopole in the slow rotation limit. It is interesting to realise that the correction to the solution relies not only on the parameter in the BI theory, but also on the radius (or the mass) of the hole. We also show that the quantum effects can undermine the energy extraction process of the magnetosphere in the non-linear theory and the extraction rate gets the maximum in the Maxwell theory. Copyright © 2019, The Authors. All rights reserved.

关键词： Magnetosphere