RAS_WEB (Page 2,680)

Properties of Cataclysmic Variables in Globular Clusters. (arXiv:2008.12772v1 [astro-ph.HE]) <a href="http://arxiv.org/find/astro-ph/1/au:+Belloni_D/0/1/0/all/0/1">Diogo Belloni</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sandoval_L/0/1/0/all/0/1">Liliana E. Rivera Sandoval</a> The study of star clusters plays an important role in our understanding of the Universe since these systems are natural laboratories for testing theories of stellar dynamics and evolution. Particularly, globular clusters (GCs) are one of the most important objects for studying the formation and the physical nature of exotic systems which in turn provide basic information and tools that can help us to understand the formation and evolution processes of star clusters themselves, galaxies and, in general, the young Universe. Among the most interesting objects in GCsRead More →

The Milky Way’s rotation curve with superfluid dark matter. (arXiv:2003.07324v2 [astro-ph.GA] UPDATED) <a href="http://arxiv.org/find/astro-ph/1/au:+Hossenfelder_S/0/1/0/all/0/1">Sabine Hossenfelder</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mistele_T/0/1/0/all/0/1">Tobias Mistele</a> Recent studies have shown that dark matter with a superfluid phase in which phonons mediate a long-distance force gives rise to the phenomenologically well-established regularities of Modified Newtonian Dynamics (MOND). Superfluid dark matter, therefore, has emerged as a promising explanation for astrophysical observations by combining the benefits of both particle dark matter and MOND, or its relativistic completions, respectively. We here investigate whether superfluid dark matter can reproduce the observed Milky Way rotation curve for $ R < 25,rm{kpc}$ and are able to answer this question inRead More →

Black holes in Einstein-aether theory: Quasinormal modes and time-domain evolution. (arXiv:2002.03450v2 [gr-qc] UPDATED) <a href="http://arxiv.org/find/gr-qc/1/au:+Churilova_M/0/1/0/all/0/1">M.S. Churilova</a> We propose accurate calculations of quasinormal modes of black holes in the Einstein-aether theory, which were previously considered in the literature, partially, with insufficient accuracy. We also show that the arbitrarily long-lived modes, quasiresonances, are allowed in the Einstein-aether theory as well and demonstrate that the asymptotic tails, unlike quasinormal frequencies, are indistinguishable from those in the Einstein theory. We propose accurate calculations of quasinormal modes of black holes in the Einstein-aether theory, which were previously considered in the literature, partially, with insufficient accuracy. We also show that theRead More →

Self-Interacting Dark Matter and the Origin of Ultra-Diffuse Galaxies NGC1052-DF2 and -DF4. (arXiv:2002.02102v2 [astro-ph.GA] UPDATED) <a href="http://arxiv.org/find/astro-ph/1/au:+Yang_D/0/1/0/all/0/1">Daneng Yang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yu_H/0/1/0/all/0/1">Hai-Bo Yu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+An_H/0/1/0/all/0/1">Haipeng An</a> Observations of ultra-diffuse galaxies NGC 1052-DF2 and -DF4 show they may contain little dark matter, challenging our understanding of galaxy formation. Using controlled N-body simulations, we explore the possibility that their properties can be reproduced through tidal stripping from the elliptical galaxy NGC 1052, in both cold dark matter (CDM) and self-interacting dark matter (SIDM) scenarios. To explain the dark matter deficiency, we find that a CDM halo must have a very low concentration so that it can lose sufficient innerRead More →

Silhouettes of invisible black holes. (arXiv:1911.07695v3 [gr-qc] UPDATED) <a href="http://arxiv.org/find/gr-qc/1/au:+Dokuchaev_V/0/1/0/all/0/1">Vyacheslav I. Dokuchaev</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Nazarova_N/0/1/0/all/0/1">Natalia O. Nazarova</a> In general relativity, isolated black holes are invisible due to an infinitely large redshift of photons propagating from the event horizon to the remote observer. However, the dark shadow (silhouette) of a black hole can be visible on the background of matter radiation lensed by the gravitational field of black holes. The black hole shadow is the celestial sphere projection of the cross section of photon capture by the black hole. If the illuminating background is far behind the black hole (at a distance much greater than the eventRead More →

Glueball scattering cross section in lattice SU(2) Yang-Mills theory. (arXiv:1910.07756v2 [hep-lat] UPDATED) <a href="http://arxiv.org/find/hep-lat/1/au:+Yamanaka_N/0/1/0/all/0/1">Nodoka Yamanaka</a>, <a href="http://arxiv.org/find/hep-lat/1/au:+Iida_H/0/1/0/all/0/1">Hideaki Iida</a>, <a href="http://arxiv.org/find/hep-lat/1/au:+Nakamura_A/0/1/0/all/0/1">Atsushi Nakamura</a>, <a href="http://arxiv.org/find/hep-lat/1/au:+Wakayama_M/0/1/0/all/0/1">Masayuki Wakayama</a> We calculate the scattering cross section between two $0^{++}$ glueballs in $SU(2)$ Yang-Mills theory on lattice at $beta = 2.1, 2.2, 2.3, 2.4$, and 2.5 using the indirect (HAL QCD) method. We employ the cluster-decomposition error reduction technique and use all space-time symmetries to improve the signal. In the use of the HAL QCD method, the centrifugal force was subtracted to remove the systematic effect due to nonzero angular momenta of lattice discretization. From the extracted interglueball potential we determine theRead More →

Impulsive wave excitation by rapidly changing granules. (arXiv:2008.12779v1 [astro-ph.SR]) <a href="http://arxiv.org/find/astro-ph/1/au:+Kwak_H/0/1/0/all/0/1">Hannah Kwak</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chae_J/0/1/0/all/0/1">Jongchul Chae</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Madjarska_M/0/1/0/all/0/1">Maria S. Madjarska</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cho_K/0/1/0/all/0/1">Kyuhyoun Cho</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Song_D/0/1/0/all/0/1">Donguk Song</a> It is not yet fully understood how magnetohydrodynamic waves in the interior and atmosphere of the Sun are excited. Traditionally, turbulent convection in the interior is considered to be the source of wave excitation in the quiet Sun. Over the last few decades, acoustic events observed in the intergranular lanes in the photosphere have emerged as a strong candidate for a wave excitation source. Here we report our observations of wave excitation by a new type of event: rapidly changingRead More →

The frequency of extreme X-ray variability of radio-quiet quasars. (arXiv:2008.12778v1 [astro-ph.HE]) <a href="http://arxiv.org/find/astro-ph/1/au:+Timlin_J/0/1/0/all/0/1">John D. Timlin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brandt_W/0/1/0/all/0/1">W. Niel Brandt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhu_S/0/1/0/all/0/1">Shifu Zhu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Liu_H/0/1/0/all/0/1">Hezhen Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Luo_B/0/1/0/all/0/1">Bin Luo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ni_Q/0/1/0/all/0/1">Qingling Ni</a> We analyze 1598 serendipitous Chandra X-ray observations of 462 radio-quiet quasars to constrain the frequency of extreme amplitude X-ray variability that is intrinsic to the quasar corona and innermost accretion flow. The quasars in this investigation are all spectroscopically confirmed, optically bright ($m_i leq$ 20.2), and contain no identifiable broad absorption lines in their optical/ultraviolet spectra. This sample includes quasars spanning $z approx$ 0.1 – 4 and probes X-ray variability on timescales of upRead More →

Investigating the relation between chaos and the three body problem. (arXiv:2008.12756v1 [nlin.CD]) <a href="http://arxiv.org/find/nlin/1/au:+Venkatesh_T/0/1/0/all/0/1">T.S.Sachin Venkatesh</a>, <a href="http://arxiv.org/find/nlin/1/au:+Vikranth_V/0/1/0/all/0/1">Vishak Vikranth</a> We review the properties of fractals, the Mandelbrot set and how deterministic chaos ties to the picture. A detailed study on three body systems, one of the major applications of chaos theory was undertaken. Systems belonging to different families produced till date were studied and their properties were analysed. We then segregated them into three classes according to their properties. We suggest that such reviews be carried out in regular intervals of time as there are an infinite number of solutions for three body systems and someRead More →

Astronomical Site Monitoring System at Lijiang Observatory. (arXiv:2004.12128v3 [astro-ph.IM] UPDATED) <a href="http://arxiv.org/find/astro-ph/1/au:+Xin_Y/0/1/0/all/0/1">Yu-Xin Xin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bai_J/0/1/0/all/0/1">Jin-Ming Bai</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lun_B/0/1/0/all/0/1">Bao-Li Lun</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fan_Y/0/1/0/all/0/1">Yu-Feng Fan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_C/0/1/0/all/0/1">Chuan-Jun Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Liu_X/0/1/0/all/0/1">Xiao-Wei Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yu_X/0/1/0/all/0/1">Xiao-Guang Yu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ye_K/0/1/0/all/0/1">Kai Ye</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Song_T/0/1/0/all/0/1">Teng-Fei Song</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chang_L/0/1/0/all/0/1">Liang Chang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+He_S/0/1/0/all/0/1">Shou-Sheng He</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mao_J/0/1/0/all/0/1">Ji-Rong Mao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Xu_L/0/1/0/all/0/1">Liang Xu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Xiong_D/0/1/0/all/0/1">Ding-Rong Xiong</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_X/0/1/0/all/0/1">Xi-Liang Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_J/0/1/0/all/0/1">Jian-Guo Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ding_X/0/1/0/all/0/1">Xu Ding</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Feng_H/0/1/0/all/0/1">Hai-Cheng Feng</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Liu_X/0/1/0/all/0/1">Xiang-Kun Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Huang_Y/0/1/0/all/0/1">Yang Huang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chen_B/0/1/0/all/0/1">Bing-Qiu Chen</a> We installed two sets of Astronomical Site Monitoring System(ASMS) at Lijiang Observatory(GMG), for the running of the 2.4-meter Lijiang optical telescope(LJT) and the 1.6-meter Multi-channel Photometric Survey Telescope (Mephisto). The Mephistro isRead More →

GRB 200415A: magnetar giant flare or short gamma-ray burst?. (arXiv:2008.12752v1 [astro-ph.HE]) <a href="http://arxiv.org/find/astro-ph/1/au:+Minaev_P/0/1/0/all/0/1">Pavel Minaev</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pozanenko_A/0/1/0/all/0/1">Alexei Pozanenko</a> A detailed analysis of the GBM/Fermi experiment data is carried out to classify GRB 200415A. It is shown that, on the one hand, this event exhibits typical for type I (short) gamma-ray bursts (GRBs) properties, such as duration, variability, and the character of spectral evolution (lag). On the other hand, the localization of the event source on the celestial plane, obtained by the triangulation method (IPN), indicates the nearby ($ D_L $ = 3.5 Mpc) galaxy NGC 253 (Sculptor) as a possible host galaxy for this burst. ItRead More →

Center-to-Limb Variation of the Inverse Evershed Flow. (arXiv:2008.12748v1 [astro-ph.SR]) <a href="http://arxiv.org/find/astro-ph/1/au:+Beck_C/0/1/0/all/0/1">C. Beck</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Choudhary_D/0/1/0/all/0/1">D.P. Choudhary</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ranganathan_M/0/1/0/all/0/1">M. Ranganathan</a> We present the properties of the inverse Evershed flow (IEF) based on the center-to-limb variation of the plasma speed and loop geometry of chromospheric superpenumbral fibrils in eleven sunspots that were located at a wide range of heliocentric angles from 12 to 79 deg. The observations were acquired at the Dunn Solar Telescope in the spectral lines of Halpha at 656nm, CaII IR at 854 nm and HeI at 1083 nm. All sunspots display opposite line-of-sight (LOS) velocities on the limb and center side with a distinctRead More →

The growth factor parametrization versus numerical solutions in flat and non-flat dark energy models. (arXiv:2008.12741v1 [astro-ph.CO]) <a href="http://arxiv.org/find/astro-ph/1/au:+Velasquez_Toribio_A/0/1/0/all/0/1">A. M. Vel&#xe1;squez-Toribio</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fabris_J/0/1/0/all/0/1">J&#xfa;lio C. Fabris</a> In the present investigation we use observational data of $ f sigma_ {8} $ to determine observational constraints in the plane $(Omega_{m0},sigma_{8})$ using two different methods: the growth factor parametrization and the numerical solutions method for density contrast, $delta_{m}$. We verified the correspondence between both methods for three models of accelerated expansion: the $Lambda CDM$ model, the $ w_{0}w_{a} CDM$ model and the running cosmological constant $RCC$ model. In all case we consider also curvature as free parameter. The study ofRead More →