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arXiv 2019年

作者： Jiao, Qian Zhao, Yinghe Lu, Nanyao Gao, Yu Salak, Dragan Zhu, Ming Zhang, Zhiyu Jiang, Xuejian Tan, Qinghua Nanjing210008 China Yunnan Observatories & Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650011 China Center for Astronomical Mega-Science CAS 20A Datun Road Chaoyang District Beijing100012 China Camino El Observatorio 1515 Las Condes Santiago Chile National Astronomical Observatories & Key Lab of Radio Astronomy CAS Beijing100012 China School of Science and Technology Kwansei Gakuin University 2-1 Gakuen SandaHyogo669-1337 Japan Institute for Astronomy University of Edinburgh Royal Observatory Blackford Hill EdinburghEH9 3HJ United Kingdom ESO Karl Schwarzschild Strasse 2 Garching MunichD-85748 Germany

We present maps of atomic carbon [C i] (3P1 → 3P0) and [C i] (3P2 → 3P1) emission (hereafter [C i] (1−0) and [C i] (2−1), respectively) at a linear resolution ∼ 1 kpc scale for a sample of one Hii, six LINER, three Seyfert and five starburst galaxies observed with the Herschel Space Observatory. We compare spatial distributions of two [C i] lines with that of CO J = 1 → 0 (hereafter CO (1−0)) emission, and find that both [C i] lines distribute similarly to CO (1−0) emission in most galaxies. We present luminosity ratio maps of L0[CI](1−0)/L0CO(1−0), L0[CI](2−1)/L0CO(1−0), L0[CI](2−1)/L0[CI](1−0) (hereafter R[CI]) and 70-to-160 µm far-infrared color of f70/f160. L0[CI](2−1)/L0CO(1−0), R[CI] and f70/f160 are centrally peaked in starbursts;whereas remain relatively constant in LINERs, indicating that star-forming activity can enhance carbon emission, especially for [C i] (2−1). We explore the correlations between the luminosities of CO (1−0) and [C i] lines, and find that L0CO(1−0) correlates tightly and almost linearly with both L0[CI](1−0) and L0[CI](2−1), suggesting that [C i] lines, similar as CO (1−0), can trace total molecular gas in Hii, LINER, Seyfert and starburst galaxies on kpc scales. We investigate the dependence of L0[CI](1−0)/L0CO(1−0), L0[CI](2−1)/L0CO(1−0) and [C i] excitation temperature of Tex on dust temperature of Tdust, and find non-correlation, a weak and modest correlation, respectively. The ratio of L0[CI](1−0)/L0CO(1−0) stays smooth distribution in most galaxies, indicating that the conversion factor of [C i] (1−0) luminosity to H2 mass (X[CI](1−0)) changes with CO (1−0) conversion factor (αCO) proportionally. Under optically thin and local thermodynamical equilibrium (LTE) assumptions, we derive a galaxy-wide average carbon excitation temperature of Tex ∼ 19.7 ± 0.5 K and an average neutral carbon abundance of X[CI]/X[H2] ∼ 2.5 ± 1.0 × 10−5 in our resolved sample, which is comparable to the usually adopted value of 3 × 10−5, but ∼ 3 times low

关键词： Galaxies

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White dwarf deflagrations for Type Iax supernovae: Polarisation signatures from the explosion and companion interaction

arXiv

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arXiv 2020年

作者： Bulla, M. Liu, Z.-W. Röpke, F.K. Sim, S.A. Fink, M. Kromer, M. Pakmor, R. Seitenzahl, I.R. Nordita KTH Royal Institute of Technology Stockholm University Roslagstullsbacken 23 StockholmSE-106 91 Sweden Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650216 China Center for Astronomical Mega-Science CAS Beijing100012 China Zentrum für Astronomie der Universität Heidelberg Institut für Theoretische Astrophysik Philosophenweg 12 Heidelberg69120 Germany Heidelberger Institut für Theoretische Studien Schloss-Wolfsbrunnenweg 35 Heidelberg69118 Germany Astrophysics Research Centre School of Mathematics and Physics Queen's University BelfastBT7 1NN United Kingdom Institut für Theoretische Physik und Astrophysik Universität Würzburg Emil-Fischer-Straße 31 WürzburgD-97074 Germany Max-Planck-Institut für Astrophysik Karl-Schwarzschild-Str. 1 GarchingD-85748 Germany School of Science University of New South Wales Australian Defence Force Academy Northcott Drive CanberraACT2600 Australia

Growing evidence suggests that Type Iax supernovae might be the result of thermonuclear deflagrations of Chandrasekhar-mass white dwarfs in binary systems. We carry out Monte Carlo radiative transfer simulations and predict spectropolarimetric features originating from the supernova explosion and subsequent ejecta interaction with the companion star. Specifically, we calculate viewing-angle dependent flux and polarisation spectra for a 3D model simulating the deflagration of a Chandrasekhar-mass white dwarf and, for a second model, simulating the ejecta interaction with a main-sequence star. We find that the intrinsic signal is weakly polarised and only mildly viewing-angle dependent, owing to the overall spherical symmetry of the explosion and the depolarising contribution of iron-group elements dominating the ejecta composition. The interaction with the companion star carves out a cavity in the ejecta and produces a detectable, but modest signal that is significant only at relatively blue wavelengths (. 5000 Å). In particular, increasingly fainter and redder spectra are predicted for observer orientations further from the cavity, while a modest polarisation signal P ∼ 0.2 per cent is found at blue wavelengths for orientations 30◦ and 45◦ away from the cavity. We find a reasonable agreement between the interaction model viewed from these orientations and spectropolarimetric data of SN 2005hk and interpret the maximum-light polarisation signal seen at blue wavelengths for this event as a possible signature of the ejecta-companion interaction. We encourage further polarimetric observations of SNe Iax to test whether our results can be extended and generalised to the whole SN Iax class. Copyright © 2020, The Authors. All rights reserved.

关键词： Radiative transfer

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Subdwarf B stars as possible surviving companions in Type Ia supernova remnants

arXiv

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arXiv 2018年

作者： Meng, Xiangcun Li, Jiao 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 20A Datun Road Chaoyang District Beijing100012 China University of Chinese Academy of Sciences Beijing100049 China

Although type Ia supernovae (SNe Ia) are so important in many astrophysical fields, a debate on their progenitor model is still endless. Searching the surviving companion in a supernova remnant (SNR) may distinguish different progenitor models, since a companion still exists in the remnant for the single-degenerate (SD) model, but does not for the double degenerate (DD) model. However, some recent surveys do not discover the surviving companions in the remnant of SN 1006 and Kepler’s supernova, which seems to disfavor the SD model. Such a result could be derived from an incorrect survey target. Here, based on the common-envelope wind SD model for SNe Ia, in which the initial binary system consists of a white dwarf (WD) and a main-sequence (MS) star, we found that the companion at the moment of supernova explosion may be a MS, red-giant (RG) or subdwarf B (sdB) star if a spin-down timescale of less than 107 yr is assumed. We show the properties of the companions at the moment of supernova explosion, which are key clues to search the surviving companions in SNRs. Here, we suggest that the sdB star may be the surviving companion in some SNRs, even if the progenitor systems are the WD + MS systems. The SNe Ia with the sdB companions may contribute to all SNe Ia as much as 22%. Copyright © 2018, The Authors. All rights reserved.

关键词： White dwarfs

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Search for γ-ray emission from dark matter particle interactions from Andromeda and Triangulum Galaxies with the Fermi Large Area Telescope

arXiv

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arXiv 2019年

作者： Mauro, Mattia Di Hou, Xian Eckner, Christopher Zaharijas, Gabrijela Charles, Eric NASA Goddard Space Flight Center GreenbeltMD20771 United States Catholic University of America Department of Physics WashingtonDC20064 United States 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 Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Center for Astrophysics and Cosmology University of Nova Gorica Vipavska 13 Nova GoricaSI-5000 Slovenia SLAC National Accelerator Laboratory Stanford University StanfordCA94305 United States

The Andromeda (M31) and Triangulum (M33) galaxies are the closest Local Group galaxies to the Milky Way, being only 785 and 870 kpc away. These two galaxies provide an independent view of high-energy processes that are often obscured in our own Galaxy, including possible signals of dark matter (DM) particle interactions. The Fermi Large Area Telescope (Fermi-LAT) preliminary eight year list of sources includes both M31, which is detected as extended with a size of about 0.4◦, and M33, which is detected as a point-like source. The spatial morphology of M31 γ-ray emission could trace a population of unresolved sources and energetic particles originating in sources not related to massive star formation. Alternatively, the γ-ray emission could also be an indication of annihilation or decay of DM particles. We investigate these two possibilities using almost 10 years of data from the Fermi LAT. An interpretation that involves only a DM γ-ray emission is in tension with the current limits from other searches, such as those targeting Milky Way dwarf spheroidal galaxies. When we include a template of astrophysical emission, tuned on γ-ray data or from observations of these galaxies in other wavelengths, we do not find any significant evidence for a DM contribution and we set limits for the annihilation cross section that probe the thermal cross section for DM masses up to a few tens of GeV in the b¯b and τ+τ− channels. For models where the DM substructures have masses above 10−6 solar masses our limits probe the DM interpretation of the Fermi LAT Galactic center excess. We provide also the lower limit for the DM decay time assuming the same spatial models of the DM distribution in M31 and M33. Copyright © 2019, The Authors. All rights reserved.

关键词： Galaxies

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Formation of hot subdwarf B stars with neutron star components

arXiv

引用

arXiv 2018年

作者： Wu, You Chen, Xuefei Li, Zhenwei Han, Zhanwen Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China University of the Chinese Academy of Science Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China

Context. Binary population synthesis predicts the existence of subdwarf B stars (sdBs) with neutron star (NS) or black hole (BH) companions. Several works have been dedicated to finding such systems, but none has been confirmed yet. Theoretically, the formation of sdBs with white dwarf (WD) and main sequence (MS) companions has been well investigated, while those with NS or BH companions remain to be explored further. Aims. We systematically investigate the formation of sdB+NS binaries from binary evolution and aim to obtain some clues for a search for such systems. Methods. We started from a series of MS+NS systems and determined the parameter spaces for producing sdB+NS binaries from the stable Roche-lobe overflow (RLOF) channel and from the common envelope (CE) ejection channel. The parameters for sdB+NS binaries were obtained from detailed binary evolution calculation with the code called modules for experiments in stellar astrophysics (MESA), and the CE parameters were given by the standard energy budget for CE evolution. The MS star had an initial mass ranging from 0.8 to 5 M. Various NS accretion efficiencies and NS masses were examined to investigate the effects they have. We show the characteristics of the produced sdB+NS systems, such as the mass of components, orbital period, the semi-amplitude of the radial velocity (K), and the spin of the NS component. Results. sdB+NS binaries can be produced either from stable RLOF or from CE ejection. In the stable RLOF channel, sdBs can be formed when the donor starts mass transfer close to the tip of the giant branch if the donor has an initial mass ≤ 2.0M. For more massive donors, sdBs can be formed when the donor starts mass transfer during the Hertzsprung gap or near the end of the MS. The orbital period of sdB+NS binaries produced in this way ranges from several days to more than 1000 days and moves toward the short-period (∼ hr) side with increasing initial MS mass. The highest K is about 150km s−1 for an MS s

关键词： Neutrons

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Black hole and neutron star binary mergers in triple systems: Merger fraction and spin-orbit misalignment

arXiv

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arXiv 2018年

作者： Liu, Bin Lai, Dong Shanghai Astronomical Observatory Chinese Academy of Sciences 80 Nandan Road Shanghai200030 China Cornell Center for Astrophysics and Planetary Science Cornell University IthacaNY14853 United States Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China Tsung-Dao Lee Institute Shanghai200240 China

Black hole (BH) mergers driven by gravitational perturbations of external companions constitute an important class of formation channels for merging BH binaries detected by LIGO. We have studied the orbital and spin evolution of binary BHs in triple systems, where the tertiary companion excites large eccentricity in the inner binary through Lidov-Kozai oscillations, causing the binary to merge via gravitational radiation. Using the single-averaged and double-averaged secular dynamics of triples (where the equations of motion are averaged over the inner orbit and both orbits, respectively), we perform a large set of numerical integrations to determine the merger window (the range of companion inclinations that allows the inner binary to merge within ∼10 Gyrs) and the merger fraction as a function of various system parameters (e.g., the binary masses m1;m2 and initial semi-major axis a0, the mass, semi-major axis and eccentricity eout of the outer companion). For typical BH binaries (m1;2 20Mo - 30Mo and a0 10 AU), the merger fraction increases rapidly with eout because of the octupole perturbation, ranging from ∼ 1% at eout = 0 to 10 - 20% at eout = 0:9. We derive the analytical expressions and approximate scaling relations for the merger window and merger fraction for systems with negligible octupole effect, and apply them to neutron star binary mergers in triples. We also follow the spin evolution of the BHs during the companion-induced orbital decay, where de-Sitter spin precession competes with Lidov-Kozai orbital precession/nutation. Starting from aligned spin axes (relative to the orbital angular momentum axis), a wide range of final spin-orbit misalignment angle θf sl can be generated when the binary enters the LIGO sensitivity band. For systems where the octupole effect is small (such as those with m1 m2 or eout ∼ 0), the distribution of θf sl peaks around 90_. As the octuple effect increases, a more isotropic distribution of final spin axis is produced. Over

关键词： Merging

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Star-formation rates of two GRB host galaxies at z ∼ 2 and a [C ii] deficit observed with ALMA

arXiv

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arXiv 2019年

作者： Hashimoto, Tetsuya Hatsukade, Bunyo Goto, Tomotsugu Kim, Seong Jin Ohta, Kouji Nagao, Tohru Kong, Albert K.H. Nakanishi, Kouichiro Mao, Jirong Institute of Astronomy National Tsing Hua University 101 Section 2. Kuang-Fu Road Hsinchu30013 Taiwan Institute of Astronomy Graduate School of Science University of Tokyo 2-21-1 Osawa Mitaka Tokyo181-0015 Japan Department of Astronomy Kyoto University Kitashirakawa-Oiwake-cho Sakyo-ku Kyoto Kyoto606-8502 Japan Research Center for Space and Cosmic Evolution Ehime University MatsuyamaEhime790-8577 Japan National Astronomical Observatory of Japan 2-21-1 Osawa Mitaka Tokyo181-8588 Japan 2-21-1 Osawa Mitaka Tokyo181-8588 Japan Yunnan Observatories Chinese Academy of Sciences Kunming Yunnan Province650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China

Event rate of long Gamma-Ray Bursts (GRBs) is expected to be an useful tracer of the cosmic star-formation history. For this purpose, it is necessary to understand what kind of star formations/galaxies are traced by GRBs. Here we report rest-frame far-infrared (FIR) continuum detections of GRB 070521 and 080207 host galaxies at z ∼ 2 with ALMA band 8 and 9. The FIR photometries provide the reliable star-formation rates (SFRs), because FIR emission is free from dust extinction and possible radio contamination from long-lived afterglows of GRBs. The spectral energy distribution fittings indicate 49.85+−722.86.33 and 123.4+−2521..1978 M yr−1 for the 070521 and 080207 hosts, respectively. The derived SFRs place them on the "main sequence" of normal star-forming galaxies at z ∼ 2. The derived SFRs are significantly lower than that of radio observations. It is inferred that the observed radio fluxes in a previous study are contaminated by the afterglows. ALMA marginally detected [C ii] 158 µm emission line from the GRB 080207 host galaxy with S/N ∼ 4. This is the first detection of [C ii] 158 µm of a GRB host at z > 2, and the second detection among known GRBs. The luminosity ratio of [C ii] 158µm to FIR is 7.5×10−4, which is one of the smallest values among galaxies at z ∼ 1 − 2 with the same FIR luminosity. The "[C ii] deficit" could be a new physical property to characterise GRB hosts at z ∼ 1 − 2. Possible parameters controlling the deficit include the metallicity, initial mass function, and gas density. Copyright © 2019, The Authors. All rights reserved.

关键词： Stars

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Disruption of a planet spiralling into its host star

arXiv

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arXiv 2018年

作者： Jia, Shi Spruit, H.C. Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Max-Planck-Institut für Astrophysik Karl-Schwarzschild-Str. 1 GarchingD-85748 Germany Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China University of Chinese Academy of Sciences Beijing100049 China

The processes leading deformation and destruction of planets spiraling into the convective envelope of their host stars are described. The planet is compressed by the ram pressure, and deformed into a attened shape for which a quantitative model is developed. Compression increases the planet's density contrast with the envelope and its gravitational binding energy. This increases the survivability especially of gas planets. An estimate is given for the depth of disruption by ram pressure, and for the subsequent fragmentation of the remnants. We show how the debris of rocky or iron planets, instead of mixing through the convection zone, sinks below the base of the convection zone. The time scale of the entire sequence of events is of the order of a few orbital times of the planet. If spiral-in of (partly) icy, rocky or iron planets has happened to the pre-main sequence Sun, it could account for the higher opacity below the base of the convection zone as inferred from helioseismology. Copyright © 2018, The Authors. All rights reserved.

关键词： Planets

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Formation of Extremely Low-Mass WDs in Double Degenerates

arXiv

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arXiv 2018年

作者： Li, Zhenwei Chen, Xuefei Chen, Hai-Liang Han, Zhanwen Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Science University of the Chinese Academy of Science Yuquan Road 19 Shijingshan Block Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Science 20A Datun Road Chaoyang District Beijing100012 China

Extremely low-mass white dwarfs (ELM WDs) are helium WDs with a mass less than ∼0.3 Mo. Most ELM WDs are found in double degenerates (DDs) in the ELM Survey led by Brown and Kilic. These systems are supposed to be significant gravitational-wave sources in the mHz frequency. In this paper, we firstly analyzed the observational characteristics of ELM WDs and found that there are two distinct groups in the ELM WD mass and orbital period plane, indicating two different formation scenarios of such objects, i.e. a stable Roche lobe overflow channel (RL channel) and common envelope ejection channel (CE channel). We then systematically investigated the formation of ELM WDs in DDs by a combination of detailed binary evolution calculation and binary population synthesis. Our study shows that the majority of ELM WDs with mass less than 0.22 Mo are formed from the RL channel. The most common progenitor mass in this way is in the range of 1.15 − 1.45 Mo and the resulting ELM WDs have a peak around 0.18 Mo when selection effects are taken into account, consistent with observations. The ELM WDs with a mass larger than 0.22 Mo are more likely to be from the CE channel and have a peak of ELM WD mass around 0.25 Mo which needs to be confirmed by future observations. By assuming a constant star formation rate of 2 Moyr−1 for a Milky Way-like galaxy, the birth rate and local density are 5 × 10−4 yr−1 and 1500 kpc−3, respectively, for DDs with an ELM WD mass less than 0.25 Mo. Copyright © 2018, The Authors. All rights reserved.

关键词： White dwarfs

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ROTATING BLACK HOLE SHADOW IN PERFECT FLUID DARK MATTER

arXiv

引用

arXiv 2018年

作者： Hou, Xian Xu, Zhaoyi Wang, Jiancheng 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 Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China

We study analytically the shadow cast by the rotating black hole in the perfect fluid dark matter. The apparent shape of the shadow depends upon the black hole spin a and the perfect fluid dark matter intensity parameter k (k > 0). In general, the shadow is a perfect circle in the non-rotating case (a = 0) and a deformed one in the rotating case (a 6= 0). The deformation gets more and more significant with the increasing a, similar to the Schwarzschild and Kerr black holes. In addition, there exists a reflection point k0. When k 0, the size of the shadow decreases with the increasing k and the distortion increases with the increasing k. When k > k0, the size of the shadow increases with the increasing k and the distortion decreases with the increasing k. Furthermore, the energy emission rate of the black hole in the perfect fluid dark matter increases with the increasing k and the peak of the emission shifts to higher frequencies. Finally, we propose that to observe the effect of the black hole spin a and the perfect fluid dark matter intensity k on the shadow of the black hole Sgr A∗ at the center of the Milky Way, highly improved techniques would be necessary for the development of future astronomical instruments. Copyright © 2018, The Authors. All rights reserved.

关键词： Galaxies

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