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1.
We extend recent work that included the effect of pressure forces to derive the precession rate of eccentric accretion discs in cataclysmic variables to the case of double degenerate systems. We find that the logical scaling of the pressure force in such systems results in predictions of unrealistically high primary masses. Using the prototype AM CVn as a calibrator for the magnitude of the effect, we find that there is no scaling that applies consistently to all the systems in the class. We discuss the reasons for the lack of a superhump period to mass ratio relationship analogous to that known for SU UMa systems and suggest that this is because these secondaries do not have a single valued mass–radius relationship. We highlight the unreliability of mass ratios derived by applying the SU UMa expression to the AM CVn binaries.  相似文献   

2.
We propose an approach for overcoming the problem of close encounters in collisional systems, globular and open star clusters. As is well known, the numerical integration step in such systems, for example, during the formation of close binary stars, begins to fragment and the rate of calculations goes down to a complete stop. We show that using the perturbation theory in the proposed approach, one can isolate the singularity and to increase considerably the integration step without losing the physical effects that affect significantly the evolution of star clusters.  相似文献   

3.
In a previous paper, using Eggleton's stellar evolution code, we have discussed the structure and evolution of low-mass W Ursae Majoris (W UMa) type contact binaries with angular momentum loss owing to gravitational radiation or magnetic braking. We find that gravitational radiation is almost insignificant for cyclic evolution of low-mass W UMa type systems, and it is possible for angular momentum to be lost from W UMa systems in a magnetic stellar wind. The weaker magnetic activity shown by observations in W UMa systems is likely caused by the lower mass of the convective envelopes in these systems than in similar but non-contact binaries. The spin angular momentum cannot be neglected at any time for W UMa type systems, especially for those with extreme mass ratios. The spin angular momenta of both components are included in this paper and they are found to have a significant influence on the cyclic evolution of W UMa systems. We investigate the influence of the energy transfer on the common convective envelopes of both components in detail. We find that the mass of the convective envelope of the primary in contact evolution is slightly more than that in poor thermal contact evolution, and that the mass of the convective envelope of the secondary in contact evolution is much less than that in poor thermal contact evolution. Meanwhile, the rate of angular momentum loss of W UMa type systems is much lower than that of poor thermal contact systems. This is indeed caused by the lower masses of the convective envelopes of the components in W UMa type systems. Although the models with angular momentum loss for W UMa systems exhibit cyclic evolution, they seem to show that a W UMa system cannot continue this type of cyclic evolution indefinitely, and it might coalesce into a fast-rotating star after about 1200 cycles of evolution (about  7.0 × 109 yr  ).  相似文献   

4.
We study spectral energy distributions of two young systems Sz54 and Sz59, that belong to Chameleon II star forming region. The results of the modeling indicate that protoplanetary disks of these systems contain gaps in the dust component. These gaps could be a result of a planetary or brown dwarf companion formation, because the companion would accumulate a disk material, moving along its orbit. In a present work we have determined physical characteristics of the disks. We also discuss possible companion characteristics, based on the geometrical parameters of the gaps.  相似文献   

5.
We derive new limits on the value of the cosmological constant, Λ, based on the Einstein bending of light by systems where the lens is a distant galaxy or a cluster of galaxies. We use an amended lens equation in which the contribution of Λ to the Einstein deflection angle is taken into account and use observations of Einstein radii around several lens systems. We use in our calculations a Schwarzschild–de Sitter vacuole exactly matched into a Friedmann–Robertson–Walker background and show that a Λ-contribution term appears in the deflection angle within the lens equation. We find that the contribution of the Λ-term to the bending angle is larger than the second-order term for many lens systems. Using these observations of bending angles, we derive new limits on the value of Λ. These limits constitute the best observational upper bound on Λ after cosmological constraints and are only two orders of magnitude away from the value determined by those cosmological constraints.  相似文献   

6.
We discuss a new method for inferring the stellar mass of a distant galaxy of known redshift based on the combination of a near-IR luminosity and multiband optical photometry. The typical uncertainty for field galaxies with I<22 in the redshift range 0相似文献   

7.
We compare the conclusions reached using the coarse-graining technique employed by Henriksen for a one degree of freedom (per particle) collisionless system to those presented in a paper by Binney based on an exact one degree of freedom model. We find agreement in detail, but in addition we show that the isolated 1D system is self-similar and therefore unrelaxed. Fine graining of this system recovers much less prominent wave-like structure than in a spherically symmetric isotropic 3D system. The rate of central flattening is also reduced in the 1D system. We take this to be evidence that relaxation of collisionless systems proceeds ultimately by way of short wavelength Landau damping. N -body systems, both real and simulated, can be trapped in an incompletely relaxed state because of a break in the cascade of energy to small scales. This may be due to the rapid dissipation of the small-scale oscillations in an isolated system to the existence of conserved quantities such as angular momentum, or to the failure in simulations to resolve sub-Jeans length scales. Such a partially relaxed state appears to be the Navarro, Frenk and White (NFW) state and is to be expected especially in young systems. The NFW core is shown to be isolated. In non-isolated systems, continuing coarse-grained relaxation should be towards a density core in solid body rotation.  相似文献   

8.
We present a simple, novel method for determining the orbital parameters of binary pulsars. This method works with any sort of orbital sampling, no matter how sparse, provided that information on the period derivatives is available with each measurement of the rotational period of the pulsar, and it is applicable to binary systems with nearly circular orbits. We use the technique to estimate precisely the hitherto unknown orbital parameters of two binary millisecond pulsars in the globular cluster 47 Tucanae, 47 Tuc S and T. The method can also be used more generally to make first-order estimates of the orbital parameters of binary systems using a minimal number of data.  相似文献   

9.
The late-stage formation of giant planetary systems is rich in interesting dynamical mechanisms. Previous simulations of three giant planets initially on quasi-circular and quasi-coplanar orbits in the gas disc have shown that highly mutually inclined configurations can be formed, despite the strong eccentricity and inclination damping exerted by the disc. Much attention has been directed to inclination-type resonance, asking for large eccentricities to be acquired during the migration of the planets. Here we show that inclination excitation is also present at small to moderate eccentricities in two-planet systems that have previously experienced an ejection or a merging and are close to resonant commensurabilities at the end of the gas phase. We perform a dynamical analysis of these planetary systems, guided by the computation of planar families of periodic orbits and the bifurcation of families of spatial periodic orbits. We show that inclination excitation at small to moderate eccentricities can be produced by (temporary) capture in inclination-type resonance and the possible proximity of the non-coplanar systems to spatial periodic orbits contributes to maintaining their mutual inclination over long periods of time.  相似文献   

10.
We study the dynamics of extended shells of relatively low-mass particles around and inside the orbit of two heavy centres of gravity (a binary) by computer simulations. The binary components are surrounded byN = 16 000 small mass particles in uniform random distribution on few spherical envelopes with different radii expanding with respective velocities. Some shells are inside the orbit of binary.We apply this model to binary galaxy systems with baryonic dark matter, e.g., massive black holes. In principle, we can apply this model to different kinds of objects (from binary star systems until superclusters of galaxies).It is shown that the shell expands homologously with a decreasing velocity and then, falls back into the binary system forming zones of compressed matter. At some moment of time there could be a collapse of these particles on to the heavier component of the binary. Further in time, some part of particles which were outside the binary orbit escape from the system. Other particles which were initially inside of the orbit are captured by binary components.We consider a number of different models with different initial parameters. For models with smaller radii of shells, about one-half of the particles escape from systems; whereas for larger values the shell disrupts as a whole. Escaping particles form collimated flows in planes of orbits of binaries. Positions of flows and directions of motion depend on positions of heavier components of binaries at the moment of a closest approach of particles and on ratios of masses of binary components.We show that during evolution of our models different kinds of structures of systems often are very similar to the observed structures of galaxies: spiral and elliptical galaxies, interacting galaxies, different kinds of flows and jets. Totally systems are expanding - after 40 periods of rotation of the binary the system expands by 300 times.  相似文献   

11.
We discuss the properties of 137 cataclysmic variables (CVs) which are included in the Sloan Digital Sky Survey (SDSS) spectroscopic data base, and for which accurate orbital periods have been measured. 92 of these systems are new discoveries from SDSS and were followed-up in more detail over the past few years. 45 systems were previously identified as CVs because of the detection of optical outbursts and/or X-ray emission, and subsequently re-identified from the SDSS spectroscopy. The period distribution of the SDSS CVs differs dramatically from that of all the previously known CVs, in particular it contains a significant accumulation of systems in the orbital period range 80–86 min. We identify this feature as the elusive 'period minimum spike' predicted by CV population models, which resolves a long-standing discrepancy between compact binary evolution theory and observations. We show that this spike is almost entirely due to the large number of CVs with very low accretion activity identified by SDSS. The optical spectra of these systems are dominated by emission from the white dwarf photosphere, and display little or no spectroscopic signature from the donor stars, suggesting very low mass companion stars. We determine the average absolute magnitude of these low-luminosity CVs at the period minimum to be  〈 Mg 〉= 11.6 ± 0.7  . Comparison of the SDSS CV sample to the CVs found in the Hamburg Quasar Survey and the Palomar Green Survey suggests that the depth of SDSS is the key ingredient resulting in the discovery of a large number of intrinsically faint short-period systems.  相似文献   

12.
Evolution of binary stars and the effect of tides on binary populations   总被引：1，自引：0，他引：1  
We present a rapid binary-evolution algorithm that enables modelling of even the most complex binary systems. In addition to all aspects of single-star evolution, features such as mass transfer, mass accretion, common-envelope evolution, collisions, supernova kicks and angular momentum loss mechanisms are included. In particular, circularization and synchronization of the orbit by tidal interactions are calculated for convective, radiative and degenerate damping mechanisms. We use this algorithm to study the formation and evolution of various binary systems. We also investigate the effect that tidal friction has on the outcome of binary evolution. Using the rapid binary code, we generate a series of large binary populations and evaluate the formation rate of interesting individual species and events. By comparing the results for populations with and without tidal friction, we quantify the hitherto ignored systematic effect of tides and show that modelling of tidal evolution in binary systems is necessary in order to draw accurate conclusions from population synthesis work. Tidal synchronism is important but, because orbits generally circularize before Roche lobe overflow, the outcome of the interactions of systems with the same semilatus rectum is almost independent of eccentricity. It is not necessary to include a distribution of eccentricities in population synthesis of interacting binaries; however, the initial separations should be distributed according to the observed distribution of semilatera recta rather than periods or semimajor axes.  相似文献   

13.
We use recent Hubble Space Telescope colour–magnitude diagrams of the resolved stellar populations of a sample of local dSph galaxies (Carina, Leo I, Leo II and Ursa Minor) to infer the star formation histories of these systems, SFR ( t ). Applying a new variational calculus maximum likelihood method, which includes a full Bayesian analysis and allows a non-parametric estimate of the function one is solving for, we infer the star formation histories of the systems studied. This method has the advantage of yielding an objective answer, as one need not assume a priori the form of the function one is trying to recover. The results are checked independently using Saha's W statistic. The total luminosities of the systems are used to normalize the results into physical units and derive SN type II rates. We derive the luminosity-weighted mean star formation history of this sample of galaxies.  相似文献   

14.
We carry out analyses on stellar and planetary properties of multiple exoplanetary systems in the currently available sample. With regards to the stars, we study their temperature, distance from the Sun, and metallicity distributions, finding that the stars that harbour multiple exoplanets tend to have subsolar metallicities, in contrast to metal-rich Hot Jupiter hosts; while non-Hot Jupiter single planet hosts form an intermediate group between these two, with approximately solar metallicities. With regards to the planetary systems, we select those with four or more planets and analyse their configurations in terms of stability (via Hill radii), compactness, and size variations. We find that most planetary pairs are stable, and that the compactness correlates to the size variation: More compact systems have more similarly sized planets and vice versa. We also investigate the spectral energy distributions of the stars hosting multiple exoplanetary systems, seeking infra-red excesses that could indicate the presence of debris disks. These disks would be leftovers from the planetary formation process, and could be considered as analogues of the Solar System’s Asteroid or Kuiper belts. We identify potential candidates for disks that are good targets for far infra-red follow-up observations to confirm their existence.  相似文献   

15.
We investigate the origin and evolution of fossil groups in a concordance ΛCDM cosmological simulation. We consider haloes with masses between  1 × 1013  and  5 × 1013  h −1 M⊙  , and study the physical mechanisms that lead to the formation of the large gap in magnitude between the brightest and the second most bright group member, which is typical for these fossil systems. Fossil groups are found to have high dark matter concentrations, which we can relate to their early formation time. The large magnitude gaps arise after the groups have built up half of their final mass, due to merging of massive group members. We show that the existence of fossil systems is primarily driven by the relatively early infall of massive satellites, and that we do not find a strong environmental dependence for these systems. In addition, we find tentative evidence for fossil group satellites falling in on orbits with typically lower angular momentum, which might lead to a more efficient merger on to the host. We find a population of groups at higher redshifts that go through a 'fossil phase': a stage where they show a large magnitude gap, which is terminated by renewed infall from their environment.  相似文献   

16.
We examine the effects of dynamical evolution in clusters on planetary systems or protoplanetary discs orbiting the components of binary stars. In particular, we look for evidence that the companions of host stars of planetary systems or discs could have their inclination angles raised from zero to between the threshold angles (39.23° and 140.77°) that can induce the Kozai mechanism. We find that up to 20 per cent of binary systems have their inclination angles increased to within the threshold range. Given that half of all extrasolar planets could be in binary systems, we suggest that up to 10 per cent of extrasolar planets could be affected by this mechanism.  相似文献   

17.
In this paper we carry out a quantitative analysis of the three-body systems and map them as a function of decaying time and initial configuration, look at this problem as an example of a simple deterministic system and ask to what extent the orbits are really predictable. We have investigated the behaviour of about 200 000 general Newtonian three-body systems using the simplest initial conditions. Within our resolution these cover all the possible states where the objects are initially at rest and have no angular momentum. We have determined the decay time-scales of the triple systems and show that the distribution of this parameter is fractal in appearance. Some areas that appear stable on large scales exhibit very narrow strips of instability and the overall pattern, dominated by resonances, reminds us of a traditional Maasai warrior shield. Also an attempt is made to recover the original starting configuration of the three bodies by backward integration. We find there are instances where the evolution to the future and to the past lead to different orbits, in spite of time symmetric initial conditions. This implies that even in simple deterministic systems there exists an arrow of time.  相似文献   

18.
We present a model describing the evolution of a Super Massive Black Holes (SMBHs) population within the framework of hierarchical models of galaxy formation. The occurrence of SMBHs binaries at different redshifts and the influence of the interacting SMBHS on the host galaxies are studied by means of Montecarlo realizations of halo merging histories, coupled with a semi-analytical treatment of the interactions between the systems. We find that the main parameters governing the coalescence timescale, and hence the fraction of binary systems, are the initial mass and the accretion history of the SMBHs. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

19.
High resolution interferometer and single-dish observations of young, deeply embedded stellar systems reveal a complex chemistry in the circumstellar environments of low to intermediate mass stars. Depletions of gas-phase molecules, grain mantle evaporation, and shock interactions actively drive chemical processes in different regions around young stars. We present results for two systems, IRAS 05338-0624 and NGC 1333 IRAS 4, to illustrate the behavior found and to examine the physical processes at work.  相似文献   

20.
We perform a stability test of triaxial models in Modified Newtonian Dynamics (MOND) using N -body simulations. The triaxial models considered here have densities that vary with   r −1  in the centre and   r −4  at large radii. The total mass of the model varies from 108 to  1010 M⊙  , representing the mass scale of dwarfs to medium-mass elliptical galaxies, respectively, from deep MOND to quasi-Newtonian gravity. We build triaxial galaxy models using the Schwarzschild technique, and evolve the systems for 200 Keplerian dynamical times (at the typical length-scale of 1.0 kpc). We find that the systems are virial overheating, and in quasi-equilibrium with the relaxation taking approximately 5 Keplerian dynamical times (1.0 kpc). For all systems, the change of the inertial (kinetic) energy is less than 10 per cent (20 per cent) after relaxation. However, the central profile of the model is flattened during the relaxation and the (overall) axis ratios change by roughly 10 per cent within 200 Keplerian dynamical times (at 1.0 kpc) in our simulations. We further find that the systems are stable once they reach the equilibrium state.  相似文献   

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