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Artículos de revistas sobre el tema "Stellar perturbation theory"

Autor: Grafiati
Publicado: 22 de febrero de 2023

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1

Magorrian, John. "Stellar dynamics in the periodic cube." Monthly Notices of the Royal Astronomical Society 507, no. 4 (2021): 4840–51. http://dx.doi.org/10.1093/mnras/stab2457.

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ABSTRACT We use the problem of dynamical friction within the periodic cube to illustrate the application of perturbation theory in stellar dynamics, testing its predictions against measurements from N-body simulations. Our development is based on the explicitly time-dependent Volterra integral equation for the cube’s linear response, which avoids the subtleties encountered in analyses based on complex frequency. We obtain an expression for the self-consistent response of the cube to steady stirring by an external perturber. From this, we show how to obtain the familiar Chandrasekhar dynamical
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2

Kolláth, Z., and J. Nuspl. "Resonance Between Pulsation Modes Due to Tidal Perturbation." Symposium - International Astronomical Union 151 (1992): 289–92. http://dx.doi.org/10.1017/s0074180900122314.

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The effect of tidal perturbation to stellar pulsation is a relatively underdeveloped problem in the theory of variable stars. We derive amplitude equations describing the resonances between pulsational modes and orbital motion taking into consideration the rotation of stars as well. In the case of δ Scuti stars the two-mode-tidal resonance was found to be the most powerful effect. If the difference between frequencies of excited and damped mode is close to the orbital frequency, parametric excitation of the damped mode may occur, while the other mode loses energy. We discuss this effect for a
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3

Georgakarakos, Nikolaos, and Siegfried Eggl. "Eccentricity estimates in hierarchical triple systems." Proceedings of the International Astronomical Union 9, S310 (2014): 88–89. http://dx.doi.org/10.1017/s1743921314007923.

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AbstractPerturbation theory in the three body problem has greatly advanced our ability to understand and model a variety of systems ranging from artificial satellites to stars and from extrasolar planets to asteroid-Jupiter interactions. In a series of papers, we developed an analytical technique for estimating the orbital eccentricity of the inner binary in hierarchical triple systems. The method combined the secular theory with calculations of short period terms. The derivation of the short term component was based on an expansion of the rate of change of the Runge-Lenz vector by using first
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4

Famaey, B., G. Monari, A. Siebert, J. B. Fouvry, and J. Binney. "Distribution functions for Galactic disc stellar populations in the presence of non-axisymmetric perturbations." Proceedings of the International Astronomical Union 13, S334 (2017): 195–98. http://dx.doi.org/10.1017/s174392131700672x.

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AbstractThe present-day response of a Galactic disc stellar population to a non-axisymmetric perturbation of the potential, in the form of a bar or spiral arms, can be treated, away from the main resonances, through perturbation theory within the action-angle coordinates of the unperturbed axisymmetric system. The first order moments of such a perturbed distribution function (DF) in the presence of spiral arms give rise to non-zero radial and vertical mean stellar velocities, called breathing modes. Such an Eulerian linearized treatment however diverges at resonances. The Lagrangian approach t
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5

Spurzem, R. "On Gravothermal Instability of Anisotropic Self-Gravitating Gas Spheres: Singular Equilibrium Solution." International Astronomical Union Colloquium 132 (1993): 241–53. http://dx.doi.org/10.1017/s0252921100066136.

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AbstractA reinvestigation of the linear perturbation theory is presented, which examines the hydrostatic readjustment of an isolated self-gravitating gas sphere to a redistribution of energy. The here presented model describes a stellar system by the common equations of gas in hydrostatic equilibrium but with the effect of the anisotropic velocity distribution on the pressure gradient. We take as equilibrium models the singular isothermal solution with and without anisotropy. The total variation of the Boltzmann entropy resulting from a perturbation of the system caused by a redistribution of
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6

Polyachenko, E. V., P. Berczik, A. Just, and I. G. Shukhman. "Simulation of the loss-cone instability in spherical systems – I. Dominating harmonic potential." Monthly Notices of the Royal Astronomical Society 492, no. 1 (2019): 645–50. http://dx.doi.org/10.1093/mnras/stz3544.

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ABSTRACT A new so-called ‘gravitational loss-cone instability’ in stellar systems has recently been investigated theoretically in the framework of linear perturbation theory and proved to be potentially important in understanding the physical processes in centres of galaxies, star clusters, and the Oort Cloud. Using N-body simulations of a toy model, we confirm previous findings for the dominating harmonic potential and go beyond the linear theory. Unlike the well-known instabilities, the new one shows no notable change in the spherical geometry of the cluster, but it significantly accelerates
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7

Malmqvist, Per-Åke. "The RASSCF, RASSI, and CASPT2 Methods Used on Small Molecules of Astrophysical Interest." International Astronomical Union Colloquium 146 (1994): 338–52. http://dx.doi.org/10.1017/s0252921100021448.

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To a quantum chemist with no particular background in astrophysics or astronomy, a brief glance at journals and textbooks in these fields shows at least three areas where computational quantum chemistry has had a valuable impact: Interstellar cloud chemistry; stellar atmosphere modelling; and chemistry in extreme conditions, such as at the surface of a neutron star. The first two uses are particularly suitable, since standard methods are directly applicable.For such problems, good calculations of potential energy as well as expectation values and matrix elements of dipole and other operators a
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8

Yavetz, Tomer D., Kathryn V. Johnston, Sarah Pearson, Adrian M. Price-Whelan, and Martin D. Weinberg. "Separatrix divergence of stellar streams in galactic potentials." Monthly Notices of the Royal Astronomical Society 501, no. 2 (2020): 1791–802. http://dx.doi.org/10.1093/mnras/staa3687.

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ABSTRACT Flattened axisymmetric galactic potentials are known to host minor orbit families surrounding orbits with commensurable frequencies. The behaviour of orbits that belong to these orbit families is fundamentally different than that of typical orbits with non-commensurable frequencies. We investigate the evolution of stellar streams on orbits near the boundaries between orbit families (separatrices) in a flattened axisymmetric potential. We demonstrate that the separatrix divides these streams into two groups of stars that belong to two different orbit families, and that as a result, the
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9

GEROYANNIS, V. S., and A. G. KATELOUZOS. "NUMERICAL TREATMENT OF HARTLE'S PERTURBATION METHOD FOR DIFFERENTIALLY ROTATING NEUTRON STARS SIMULATED BY GENERAL-RELATIVISTIC POLYTROPIC MODELS." International Journal of Modern Physics C 19, no. 12 (2008): 1863–908. http://dx.doi.org/10.1142/s0129183108013370.

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We compute general-relativistic polytropic models of differentially rotating neutron stars. A brief description of our numerical treatment is given as follows. First, the relativistic Oppenheimer–Volkoff equations of hydrostatic equilibrium are solved for nonrotating models obeying the well-known polytropic equation of state. Then, uniform rotation assumed for such models is treated in the framework of Hartle's perturbation method; thus, corrections to mass and radius, owing to spherical and quadrupole deformations, are calculated. Next, a perturbative approach to the stellar structure up to t
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10

Soufi, F., M. J. Goupil, W. A. Dziembowski, and R. Sienkiewicz. "Consequences of Rapid Rotation on Mode Identification." International Astronomical Union Colloquium 155 (1995): 321–22. http://dx.doi.org/10.1017/s0252921100037301.

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The present work deals with the effect of rotation on the adiabatic oscillation frequencies of stellar models. Here, rotation, as described in a perturbation theory, is said to be rapid in the sense that second order perturbation effects have to be taken into account. Rotation has two second order effects on the oscillation frequencies: departure from equidistance within a given multiplet split by rotation and an overall shift of the multiplet itself. The first effect has been investigated for realistic models of δ Scuti stars in uniform rotation (Dziembowski & Goode, 1992), whereas H. Sai
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11

Hamers, Adrian S., and Johan Samsing. "Analytic computation of the secular effects of encounters on a binary: features arising from second-order perturbation theory." Monthly Notices of the Royal Astronomical Society 487, no. 4 (2019): 5630–48. http://dx.doi.org/10.1093/mnras/stz1646.

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AbstractBinary–single interactions play a crucial role in the evolution of dense stellar systems such as globular clusters. In addition, they are believed to drive black hole (BH) binary mergers in these systems. A subset of binary–single interactions are secular encounters, for which the third body approaches the binary on a relatively wide orbit, and such that it is justified to average the equations of motion over the binary’s orbital phase. Previous works used first-order (FO) perturbation theory to compute the effects of such secular encounters on the binary. However, this approach can br
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12

Yang, Tianyi, Michael J. Hudson, and Niayesh Afshordi. "How dark are filaments in the cosmic web?" Monthly Notices of the Royal Astronomical Society 498, no. 3 (2020): 3158–70. http://dx.doi.org/10.1093/mnras/staa2547.

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ABSTRACT The cold dark matter model predicts that dark matter haloes are connected by filaments. Direct measurements of the masses and structure of these filaments are difficult, but recently several studies have detected these dark-matter-dominated filaments using weak lensing. Here we study the efficiency of galaxy formation within the filaments by measuring their total mass-to-light ratios and stellar mass fractions. Specifically, we stack pairs of luminous red galaxies (LRGs) with a typical separation on the sky of 8 h−1 Mpc. We stack background galaxy shapes around pairs to obtain mass ma
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13

Vavrukh, M., D. Dzikovskyi, and S. Smerechynskyi. "White dwarfs with rapid rotation." Mathematical Modeling and Computing 9, no. 2 (2022): 278–302. http://dx.doi.org/10.23939/mmc2022.02.278.

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A new analytical approach for calculation of white dwarfs characteristics that accounts for two important competing factors — axial rotation and Coulomb interparticle interactions, is proposed. The feature of our approach is simultaneous usage of differential and integral forms of equilibrium equation. In dimensionless form the differential equilibrium equation is strongly nonlinear inhomogeneous equation of the second order in partial derivatives with two dimensionless parameters — the relativistic parameter in stellar center $x_0$ and dimensionless angular velocity $\Omega$. In inner stellar
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14

Ahmedov, Bobomurat J., Roustam M. Zalaletdinov, Zafar Ya Turakulov, Salakhutdin N. Nuritdinov, and Karomat T. Mirtadjieva. "Relativistic astrophysics and cosmology in Uzbekistan." Proceedings of the International Astronomical Union 2, SPS5 (2006): 159–66. http://dx.doi.org/10.1017/s174392130700693x.

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AbstractThe theoretical results obtained in Uzbekistan in the field of relativistic astrophysics and cosmology are presented. In particular electrostatic plasma modes along the open field lines of a rotating neutron star and Goldreich-Julian charge density in general relativity are analyzed for the rotating and oscillating magnetized neutron stars. The impact that stellar oscillations of different type (radial, toroidal and spheroidal ones) have on electric and magnetic fields external to a relativistic magnetized star has been investigated. A study of the dynamical evolution and the number of
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15

Hamers, Adrian S., and Johan Samsing. "Analytic computation of the secular effects of encounters on a binary: third-order perturbation, octupole, and post-Newtonian terms; steady-state distribution." Monthly Notices of the Royal Astronomical Society 488, no. 4 (2019): 5192–209. http://dx.doi.org/10.1093/mnras/stz2029.

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ABSTRACTDense stellar systems such as globular clusters are believed to harbour merging binary black holes (BHs). The evolution of such binaries is driven by interactions with other stars, most notably, binary-single interactions. Traditionally, so-called ‘strong’ interactions are believed to be the driving force in this evolution. However, we recently showed that more distant, i.e. ‘weak’ or ‘secular’ encounters, can have important implications for the properties of merging BH binaries in globular clusters. This motivates more detailed understanding of the effects of secular encounters on a b
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16

Damiani, C., R. H. Cameron, A. C. Birch, and L. Gizon. "Rossby modes in slowly rotating stars: depth dependence in distorted polytropes with uniform rotation." Astronomy & Astrophysics 637 (May 2020): A65. http://dx.doi.org/10.1051/0004-6361/201936251.

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Context. Large-scale Rossby waves have recently been discovered based on measurements of horizontal surface and near-surface solar flows. Aims. We are interested in understanding why it is only equatorial modes that are observed and in modelling the radial structure of the observed modes. To this aim, we have characterised the radial eigenfunctions of r modes for slowly rotating polytropes in uniform rotation. Methods. We followed Provost et al. (1981, A&A, 94, 126) and considered a linear perturbation theory to describe quasi-toroidal stellar adiabatic oscillations in the inviscid case. W
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17

Li, Ya-Ping, Yi-Xian Chen, Douglas N. C. Lin, and Zhuoxiao Wang. "Spin Evolution of Stellar-mass Black Holes Embedded in AGN Disks: Orbital Eccentricity Produces Retrograde Circumstellar Flows." Astrophysical Journal Letters 928, no. 1 (2022): L1. http://dx.doi.org/10.3847/2041-8213/ac5b61.

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Abstract The spin evolution of stellar-mass black holes (sBHs) embedded in AGN accretion disks is an important process relevant to the production of gravitational waves from binary BH (BBH) merger events through the AGN channel. Because embedded sBHs are surrounded by circumstellar disks (CSDs), the rotation of CSD gas flows determines the direction of the angular momentum it accretes. In this Letter, we use global 2D hydrodynamic simulations to show that while a disk-embedded sBH on a circular orbit transforms the initial retrograde Keplerian shear of the background accretion disk into a prog
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18

Azmat, Hina, M. Zubair, and Ifra Noureen. "Dynamics of shearing viscous fluids in f(R,T) gravity." International Journal of Modern Physics D 27, no. 01 (2017): 1750181. http://dx.doi.org/10.1142/s0218271817501814.

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In this paper, we have analyzed the dynamical stability of shearing viscous anisotropic fluid with cylindrical symmetry in [Formula: see text] theory. We have chosen two viable [Formula: see text] models for dynamical analysis, and explored their nature and role for stable stellar configuration. Modified field equations and corresponding dynamical equations have been constructed, perturbation approach is adopted to deal with complexity of these equations. With the help of perturbed dynamical equations, the evolution equation has been established to analyze the role of shear viscosity and press
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19

Regály, Zsolt, Viktória Fröhlich, and József Vinkó. "Lost in Space: Companions’ Fatal Dance around Massive Dying Stars." Astrophysical Journal 941, no. 2 (2022): 121. http://dx.doi.org/10.3847/1538-4357/aca1ba.

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Abstract Discoveries of planet and stellar remnant hosting pulsars challenge our understanding, as the violent supernova explosion that forms the pulsar presumably destabilizes the system. Type II supernova explosions lead to the formation of eccentric bound systems, free-floating planets, neutron stars, pulsars, and white dwarfs. Analytical and numerical studies of high mass-loss rate systems based on perturbation theory so far have focused mainly on planet-star systems. In this paper, we extend our understanding of the fate of planet-star and binary systems by assuming a homologous envelope
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20

Casals, Marc. "A self-force approach to the two-body problem: The Green function method." International Journal of Modern Physics D 25, no. 09 (2016): 1641015. http://dx.doi.org/10.1142/s0218271816410157.

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The inspiral of a stellar-mass astrophysical object into a massive black hole may be modeled within perturbation theory of General Relativity via the so-called self-force. In this paper, we present a novel method for the calculation of the self-force which is based on the Green function (GF) of the wave equation satisfied by the field created by the smaller object. We review the results in [M. Casals, S. Dolan, A. C. Ottewill and B. Wardell, Phys. Rev. D 88 (2013) 044022; B. Wardell, C. R. Galley, A. Zenginoğlu, M. Casals, S. R. Dolan and A. C. Ottewill, Phys. Rev. D 89 (2014) 084021] on the G
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21

Macedo, Caio F. B., Luís C. B. Crispino, Vitor Cardoso, Hirotada Okawa, and Paolo Pani. "Evidence for event horizons: Long-lived modes in ultracompact objects." International Journal of Modern Physics D 24, no. 09 (2015): 1542023. http://dx.doi.org/10.1142/s0218271815420237.

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Gravitational compact astrophysical objects are excellent laboratories to test the strong field regime of theories of gravity. Among these compact objects, lies the ultracompact class: stellar structures that possess a light ring (circular null geodesic). Such ultracompact stars were presented in literature in the earlier solutions of general relativity, and some are claimed to be good candidates to the supermassive objects present at the center of galaxies. In this paper, we present evidences for the claim that compact objects with a light ring should be black holes, based on the existence of
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22

Chiba, Rimpei, Jennifer K. S. Friske, and Ralph Schönrich. "Resonance sweeping by a decelerating Galactic bar." Monthly Notices of the Royal Astronomical Society 500, no. 4 (2020): 4710–29. http://dx.doi.org/10.1093/mnras/staa3585.

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ABSTRACT We provide the first quantitative evidence for the deceleration of the Galactic bar from local stellar kinematics in agreement with dynamical friction by a typical dark matter halo. The kinematic response of the stellar disc to a decelerating bar is studied using secular perturbation theory and test particle simulations. We show that the velocity distribution at any point in the disc affected by a naturally slowing bar is qualitatively different from that perturbed by a steadily rotating bar with the same current pattern speed Ωp and amplitude. When the bar slows down, its resonances
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23

Ma, Xiao-Yu, Weikai Zong, Jian-Ning Fu, et al. "K2 Photometry on Oscillation Mode Variability: The New Pulsating Hot B Subdwarf Star EPIC 220422705." Astrophysical Journal 933, no. 2 (2022): 211. http://dx.doi.org/10.3847/1538-4357/ac75b8.

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Abstract We present an analysis of oscillation mode variability in the hot B subdwarf star EPIC 220422705, a new pulsator discovered from ∼78 days of K2 photometry. The high-quality light curves provide a detection of 66 significant independent frequencies, from which we identified nine incomplete potential triplets and three quintuplets. Those g- and p-multiplets give rotation periods of ∼36 and 29 days in the core and at the surface, respectively, potentially suggesting a slightly differential rotation. We derived a period spacing of 268.5 s and 159.4 s for the sequence of dipole and quadrup
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24

Gourgoulhon, E., A. Le Tiec, F. H. Vincent, and N. Warburton. "Gravitational waves from bodies orbiting the Galactic center black hole and their detectability by LISA." Astronomy & Astrophysics 627 (July 2019): A92. http://dx.doi.org/10.1051/0004-6361/201935406.

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Aims. We present the first fully relativistic study of gravitational radiation from bodies in circular equatorial orbits around the massive black hole at the Galactic center, Sgr A* and we assess the detectability of various kinds of objects by the gravitational wave detector LISA. Methods. Our computations are based on the theory of perturbations of the Kerr spacetime and take into account the Roche limit induced by tidal forces in the Kerr metric. The signal-to-noise ratio in the LISA detector, as well as the time spent in LISA band, are evaluated. We have implemented all the computational t
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25

Voisin, Guillaume, René P. Breton, and Charlotte Summers. "A spider timing model: accounting for quadrupole deformations and relativity in close pulsar binaries." Monthly Notices of the Royal Astronomical Society 492, no. 2 (2019): 1550–65. http://dx.doi.org/10.1093/mnras/stz3430.

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ABSTRACT Spider millisecond pulsars are, along with some eclipsing post-common envelope systems and cataclysmic variables, part of an expanding category of compact binaries with low-mass companions for which puzzling timing anomalies have been observed. The most prominent type of irregularities seen in them are orbital period variations, a phenomenon which has been proposed to originate from changes in the gravitational quadrupole moment of the companion star. A physically sound modelling of the timing of these systems is key to understanding their structure and evolution. In this paper we arg
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26

Roxburgh, I. W., and S. V. Vorontsov. "Asymptotic Theory of Low-Degree Stellar Acoustic Oscillations." International Astronomical Union Colloquium 137 (1993): 535–37. http://dx.doi.org/10.1017/s0252921100018364.

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AbstractWe extend the second-order asymptotic description developed by Tassoul (1980, 1990) to the forth order, taking into account both gravity perturbations and realistic (non-polytropic) structure of the stellar envelope. We examine the accuracy of the asymptotic description by the direct computations for a solar model.
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27

Ledinauskas, E., and K. Zubovas. "Reignited star formation in dwarf galaxies that were quenched during reionization." Astronomy & Astrophysics 615 (July 2018): A64. http://dx.doi.org/10.1051/0004-6361/201832824.

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Context. Irregular dwarf galaxies of the Local Group have very varied properties and star formation histories. Some of them formed the majority of their stars very late compared to others. Extreme examples of this are Leo A and Aquarius, which reached the peak of star formation at z < 1 (more than 6 Gyr after the Big Bang). This fact seemingly challenges the ΛCDM cosmological framework because the dark matter halos of these galaxies on average should assemble the majority of their masses before z ~ 2 (<3 Gyr after the Big Bang). Aims. We investigate whether the delayed star formation his
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28

Driessen, F. A., J. O. Sundqvist, and N. D. Kee. "Theoretical wind clumping predictions of OB supergiants from line-driven instability simulations across the bi-stability jump." Astronomy & Astrophysics 631 (November 2019): A172. http://dx.doi.org/10.1051/0004-6361/201936331.

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Context. The behaviour of mass loss across the so-called bi-stability jump, where iron recombines from Fe IV to Fe III, is a key uncertainty in models of massive stars. Specifically, while an increase in mass loss is theoretically predicted, this has not yet been observationally confirmed. However, radiation-driven winds of hot massive stars are known to exhibit clumpy structures triggered by the line-deshadowing instability (LDI). This wind clumping severely affects empirical mass-loss rates inferred from ρ2-dependent spectral diagnostics. Thus, if clumping properties differ significantly for
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29

Gurzadyan, V. G. "A Physicist’s View of Stellar Dynamics: Dynamical Instability of Stellar Systems." Highlights of Astronomy 13 (2005): 354–57. http://dx.doi.org/10.1017/s1539299600015951.

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AbstractI argue that the widely adopted framework of stellar dynamics survived since 1940s, is not fitting the current knowledge on non-linear systems. Borrowed from plasma physics when several fundamental features of perturbed non-linear systems were unknown, that framework ignores the difference in the role of perturbations in two different classes of systems, in plasma with Debye screening and gravitating systems with no screening. Now, when the revolutionary role of chaotic effects is revealed even in planetary dynamics i.e. for nearly integrable systems, one would expect that for stellar
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30

Hjorth, Maria, Simon Albrecht, Teruyuki Hirano, et al. "A backward-spinning star with two coplanar planets." Proceedings of the National Academy of Sciences 118, no. 8 (2021): e2017418118. http://dx.doi.org/10.1073/pnas.2017418118.

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It is widely assumed that a star and its protoplanetary disk are initially aligned, with the stellar equator parallel to the disk plane. When observations reveal a misalignment between stellar rotation and the orbital motion of a planet, the usual interpretation is that the initial alignment was upset by gravitational perturbations that took place after planet formation. Most of the previously known misalignments involve isolated hot Jupiters, for which planet–planet scattering or secular effects from a wider-orbiting planet are the leading explanations. In theory, star/disk misalignments can
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31

Kolláth, Z. "On the Observed Complexity of Chaotic Stellar Pulsation." International Astronomical Union Colloquium 134 (1993): 141–43. http://dx.doi.org/10.1017/s0252921100014044.

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The existence of some variable stars producing very complicated light curves is well known. Theoretical calculations suggest that the irregular behaviour of the pulsation models in the RV Tauri and W Virginis regime is low dimensional is the result of period-doubling or tangent bifurcations (see e.g. Buchler and Kovács 1987, Kovács and Buchler 1988, Tanaka and Takeuti 1988).The light variation of the RV Tauri star R Scuti covering 150 years was analyzed by Kolláth (1990). A striking similarity was found between the reconstructed attractor of the Rössler model and that of the light variation of
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32

Collins, Benjamin F., and Re'em Sari. "A UNIFIED THEORY FOR THE EFFECTS OF STELLAR PERTURBATIONS AND GALACTIC TIDES ON OORT CLOUD COMETS." Astronomical Journal 140, no. 5 (2010): 1306–12. http://dx.doi.org/10.1088/0004-6256/140/5/1306.

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33

Pétri, J. "Spheroidal magnetic stars rotating in vacuum." Astronomy & Astrophysics 657 (January 2022): A73. http://dx.doi.org/10.1051/0004-6361/202141911.

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Context. Gravity shapes stars to become almost spherical because of the isotropic nature of gravitational attraction in Newton’s theory. However, several mechanisms break this isotropy, such as their rotation generating a centrifugal force, magnetic pressure, or anisotropic equations of state. The stellar surface therefore slightly or significantly deviates from a sphere depending on the strength of these anisotropic perturbations. Aims. In this paper, we compute analytical and numerical solutions of the electromagnetic field produced by a rotating spheroidal star of oblate or prolate nature.
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34

Schou, J. "Modeling and use of stellar oscillation visibilities." Astronomy & Astrophysics 617 (September 2018): A111. http://dx.doi.org/10.1051/0004-6361/201730569.

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Context. Recently our ability to study stars using asteroseismic techniques has increased dramatically, largely through the use of space based photometric observations. Work has also been performed using ground based spectroscopic observations and more is expected in the near future from the SONG network. Unfortunately, the intensity observations have an inferior signal-to-noise ratio and details of the observations do not agree with theory, while the data analysis used in the spectroscopic method has often been based on overly simple models of the spectra. Aims. The aim is to improve the reli
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35

Meng, Xi, and Oleg Y. Gnedin. "Origin of giant stellar clumps in high-redshift galaxies." Monthly Notices of the Royal Astronomical Society 494, no. 1 (2020): 1263–75. http://dx.doi.org/10.1093/mnras/staa776.

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ABSTRACT We examine the nature of kpc-scale clumps seen in high-redshift galaxies using a suite of cosmological simulations of galaxy formation. We identify rest-frame UV clumps in mock HST images smoothed to 500 pc resolution, and compare them with the intrinsic 3D clumps of young stars identified in the simulations with 100 pc resolution. According to this comparison for the progenitors of Milky Way-sized galaxies probed by our simulations, we expect that the stellar masses of the observed clumps are overestimated by as much as an order of magnitude, and that the sizes of these clumps are al
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36

Fernández, Julio A. "The formation and dynamical survival of the comet cloud." International Astronomical Union Colloquium 83 (1985): 45–70. http://dx.doi.org/10.1017/s0252921100083792.

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AbstractThe theory of a huge reservoir of comets (the “comet cloud”) extending to almost interstellar distances is analyzed, paying special attention to its dynamical stability, formation process and orbital properties of the incoming cloud comets. The perturbing influence of passing stars and giant molecular clouds is considered. Giant molecular clouds may be an important perturbing element of the comet cloud, although they do not seem to change drastically former studies including only stellar perturbations. The more tightly bound inner portions of the comet cloud, say within 104 AU, would h
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37

Meng, Zeyang, Ji-Wei Xie, and Ji-Lin Zhou. "Planetary Survival and Ejection in Transient Multiple Star Systems." Proceedings of the International Astronomical Union 8, S293 (2012): 174–76. http://dx.doi.org/10.1017/s1743921313012775.

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AbstractMany planets have been detected in close binary stars with separation only ~20 AU. These discoveries challenge the current theory of planet formation because binary stars with such an close separation are thought to have strong perturbations and thus inhibit planet formation around them. To address this issue, another scenario had been suggested: the binary separation was wider enough for binary formation in early stages, but it shrank to the present one after a transient triple star phase (stellar scattering phase). Here, we investigate how could planet survive or be ejected under thi
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38

Hamilton, Chris, and Roman R. Rafikov. "Secular dynamics of binaries in stellar clusters – III. Doubly averaged dynamics in the presence of general-relativistic precession." Monthly Notices of the Royal Astronomical Society 505, no. 3 (2021): 4151–77. http://dx.doi.org/10.1093/mnras/stab1284.

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ABSTRACT Secular evolution of binaries driven by an external (tidal) potential is a classic astrophysical problem. Tidal perturbations can arise due to an external point mass, as in the Lidov–Kozai (LK) theory of hierarchical triples, or due to an extended stellar system (e.g. galaxy or globular cluster) in which the binary resides. For many applications, general-relativistic (GR) apsidal precession is important, and has been accounted for in some LK calculations. Here, we generalize and extend these studies by exploring in detail the effect of GR precession on (quadrupole-level) tidal evoluti
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39

FORBES, LAWRENCE K. "RAYLEIGH–TAYLOR INSTABILITIES IN AXI-SYMMETRIC OUTFLOW FROM A POINT SOURCE." ANZIAM Journal 53, no. 2 (2011): 87–121. http://dx.doi.org/10.1017/s1446181112000090.

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AbstractThis paper studies outflow of a light fluid from a point source, starting from an initially spherical bubble. This region of light fluid is embedded in a heavy fluid, from which it is separated by a thin interface. A gravitational force directed radially inward toward the mass source is permitted. Because the light inner fluid is pushing the heavy outer fluid, the interface between them may be unstable to small perturbations, in the Rayleigh–Taylor sense. An inviscid model of this two-layer flow is presented, and a linearized solution is developed for early times. It is argued that the
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40

Altiparmak, Sinan, Christian Ecker, and Luciano Rezzolla. "On the Sound Speed in Neutron Stars." Astrophysical Journal Letters 939, no. 2 (2022): L34. http://dx.doi.org/10.3847/2041-8213/ac9b2a.

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Abstract Determining the sound speed c s in compact stars is an important open question with numerous implications on the behavior of matter at large densities and hence on gravitational-wave emission from neutron stars. To this scope, we construct more than 107 equations of state (EOSs) with continuous sound speed and build more than 108 nonrotating stellar models consistent not only with nuclear theory and perturbative QCD, but also with astronomical observations. In this way, we find that EOSs with subconformal sound speeds, i.e., with c s 2 < 1 / 3 within the stars, are possible in prin
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41

Mathis, S., L. Bugnet, V. Prat, K. Augustson, S. Mathur, and R. A. Garcia. "Probing the internal magnetism of stars using asymptotic magneto-asteroseismology." Astronomy & Astrophysics 647 (March 2021): A122. http://dx.doi.org/10.1051/0004-6361/202039180.

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Context. Our knowledge of the dynamics of stars has undergone a revolution through the simultaneous large amount of high-quality photometric observations collected by space-based asteroseismology and ground-based high-precision spectropolarimetry. They allowed us to probe the internal rotation of stars and their surface magnetism in the whole Hertzsprung-Russell diagram. However, new methods should still be developed to probe the deep magnetic fields in these stars. Aims. Our goal is to provide seismic diagnoses that allow us to probe the internal magnetism of stars. Methods. We focused on asy
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42

Manchester, R. N. "Pulsars and gravity." International Journal of Modern Physics D 24, no. 06 (2015): 1530018. http://dx.doi.org/10.1142/s0218271815300189.

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Pulsars are wonderful gravitational probes. Their tiny size and stellar mass give their rotation periods a stability comparable to that of atomic frequency standards. This is especially true of the rapidly rotating "millisecond pulsars" (MSPs). Many of these rapidly rotating pulsars are in orbit with another star, allowing pulsar timing to probe relativistic perturbations to the orbital motion. Pulsars have provided the most stringent tests of theories of relativistic gravitation, especially in the strong-field regime, and have shown that Einstein's general theory of relativity is an accurate
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43

Van Hamme, W., R. E. Wilson, and R. M. Branly. "Multiple Probes of the AS Cam Dynamical Problem." International Astronomical Union Colloquium 187 (2002): 155–60. http://dx.doi.org/10.1017/s0252921100001342.

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AbstractAS Camelopardalis is notorious for its apparent disregard for the theory of apsidal motion. The orbit of this 3.43-day double-lined eclipsing binary (B8V + B9.5V) rotates approximately 15° per century, which is only 0.3 to 0.4 as fast as predicted (classical + relativistic). Our dynamical program explores, as have others, the suggestion that a third star perturbs the orbit of the eclipsing pair and slows its apsidal motion, dω/dt. On the observational side, we unify the process of extracting apsidal motion and light-time effect parameters from eclipse minima by directly including a thi
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44

Irwin, Alan W., Don A. VandenBerg та Ana M. Larson. "A Program for the Analysis of Long-Period Binaries: The Case of ϒ Delphini". International Astronomical Union Colloquium 170 (1999): 297–307. http://dx.doi.org/10.1017/s0252921100048703.

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AbstractBinary systems can be analyzed like clusters but with additional constraints from the orbit. The theories of stellar interiors and atmospheres are used to analyze the color-magnitude diagram and spectra to test the consistency of theory and observation and also to provide results on the distance, chemical composition, age, and individual masses, radii, and effective temperatures. Given the total mass resulting from the theoretical analysis, it is possible to determine the complete orbit of even long-period binaries if at least 6 components of the position, velocity and acceleration vec
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45

Prat, V., S. Mathis, F. Lignières, J. Ballot, and P. M. Culpin. "Period spacing of gravity modes strongly affected by rotation." Astronomy & Astrophysics 598 (February 2017): A105. http://dx.doi.org/10.1051/0004-6361/201629637.

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Context. As of today, asteroseismology mainly allows us to probe the internal rotation of stars when modes are only weakly affected by rotation using perturbative methods. Such methods cannot be applied to rapidly rotating stars, which exhibit complex oscillation spectra. In this context, the so-called traditional approximation, which neglects the terms associated with the latitudinal component of the rotation vector, describes modes that are strongly affected by rotation. This approximation is sometimes used for interpreting asteroseismic data, however, its domain of validity is not establish
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46

Geen, Sam, and Alex de Koter. "Bottling the champagne: dynamics and radiation trapping of wind-driven bubbles around massive stars." Monthly Notices of the Royal Astronomical Society 509, no. 3 (2021): 4498–514. http://dx.doi.org/10.1093/mnras/stab3245.

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ABSTRACT In this paper, we make predictions for the behaviour of wind bubbles around young massive stars using analytic theory. We do this in order to determine why there is a discrepancy between theoretical models that predict that winds should play a secondary role to photoionization in the dynamics of H iiregions, and observations of young H iiregions that seem to suggest a driving role for winds. In particular, regions such as M42 in Orion have neutral hydrogen shells, suggesting that the ionizing radiation is trapped closer to the star. We first derive formulae for wind bubble evolution i
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47

McCarthy, Ian G., and Andreea S. Font. "The imprint of dark subhaloes on the circumgalactic medium." Monthly Notices of the Royal Astronomical Society 499, no. 3 (2020): 3255–66. http://dx.doi.org/10.1093/mnras/staa2767.

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ABSTRACT The standard model of cosmology, the Λ cold dark matter (ΛCDM) model, robustly predicts the existence of a multitude of dark matter ‘subhaloes’ around galaxies like the Milky Way. A wide variety of observations have been proposed to look for the gravitational effects such subhaloes would induce in observable matter. Most of these approaches pertain to the stellar or cool gaseous phases of matter. Here we propose a new approach, which is to search for the perturbations that such dark subhaloes would source in the warm/hot circumgalactic medium (CGM) around normal galaxies. With a combi
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48

Verliat, Antoine, Patrick Hennebelle, Anaëlle J. Maury, and Mathilde Gaudel. "Protostellar disk formation by a nonrotating, nonaxisymmetric collapsing cloud: model and comparison with observations." Astronomy & Astrophysics 635 (March 2020): A130. http://dx.doi.org/10.1051/0004-6361/201936394.

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Context. Planet-forming disks are fundamental objects that are thought to be inherited from large scale rotation through the conservation of angular momentum during the collapse of a prestellar dense core. Aims. We investigate the possibility for a protostellar disk to be formed from a motionless dense core that contains nonaxisymmetric density fluctuations. The rotation is thus generated locally by the asymmetry of the collapse. Methods. We study the evolution of the angular momentum in a nonaxisymmetric collapse of a dense core from an analytical point of view. To test the theory, we perform
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49

Mohayaee, Roya, Mohamed Rameez, and Subir Sarkar. "Do supernovae indicate an accelerating universe?" European Physical Journal Special Topics 230, no. 9 (2021): 2067–76. http://dx.doi.org/10.1140/epjs/s11734-021-00199-6.

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AbstractIn the late 1990’s, observations of two directionally-skewed samples of, in total, 93 Type Ia supernovae were analysed in the framework of the Friedmann–Lemaître–Robertson–Walker (FLRW) cosmology. Assuming these to be ‘standard(isable) candles’ it was inferred that the Hubble expansion rate is accelerating as if driven by a positive Cosmological Constant $$\varLambda $$ Λ in Einstein’s theory of gravity. This is still the only direct evidence for the ‘dark energy’ that is the dominant component of today’s standard $$\varLambda $$ Λ CDM cosmological model. Other data such as baryon acou
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50

Mathew, Arun, Muhammed Shafeeque, and Malay K. Nandy. "Stellar structure of quark stars in a modified Starobinsky gravity." European Physical Journal C 80, no. 7 (2020). http://dx.doi.org/10.1140/epjc/s10052-020-8130-4.

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Abstract We propose a form of gravity–matter interaction given by $$\omega RT$$ωRT in the framework of f(R, T) gravity and examine the effect of such interaction in spherically symmetric compact stars. Treating the gravity–matter coupling as a perturbative term on the background of Starobinsky gravity, we develop a perturbation theory for equilibrium configurations. For illustration, we take the case of quark stars and explore their various stellar properties. We find that the gravity–matter coupling causes an increase in the stable maximal mass which is relevant for recent observations on bin
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