Showing papers in "Astrophysics and Space Science in 2008"
TL;DR: The Aarhus adiabatic pulsation code as discussed by the authors has been developed for more than a decade and has seen substantial use at a number of installations, including the HELAS Coordination Action.
Abstract: Development of the Aarhus adiabatic pulsation code started around 1978. Although the main features have been stable for more than a decade, development of the code is continuing, concerning numerical properties and output. The code has been provided as a generally available package and has seen substantial use at a number of installations. Further development of the package, including bringing the documentation closer to being up to date, is planned as part of the HELAS Coordination Action.
403 citations
TL;DR: In this paper, the Geneva stellar evolution code with special emphasis on the modeling of solar-type stars is presented. And the basic input physics used in the Geneva code as well as the modelling of atomic diffusion is first discussed.
Abstract: This paper presents the Geneva stellar evolution code with special emphasis on the modeling of solar-type stars. The basic input physics used in the Geneva code as well as the modeling of atomic diffusion is first discussed. The physical description of rotation is then presented. Finally, the modeling of magnetic instabilities and transport of angular momentum by internal gravity waves is briefly summarized.
295 citations
TL;DR: The standard solar model serves as the most basic benchmark to test the accurateness of the Garching Stellar Evolution Code and is presented, too.
Abstract: We describe the Garching Stellar Evolution Code. General features, treatment of the microphysics, details of the numerical solution, handling and particularities are discussed. The standard solar model serves as the most basic benchmark to test the accurateness of the code and is presented, too.
288 citations
TL;DR: The Aarhus code as mentioned in this paper is the result of a long development, starting in 1974, and still ongoing, and integrates the computation of adiabatic oscillations for specified models as part of the code.
Abstract: The Aarhus code is the result of a long development, starting in 1974, and still ongoing. A novel feature is the integration of the computation of adiabatic oscillations for specified models as part of the code. It offers substantial flexibility in terms of microphysics and has been carefully tested for the computation of solar models. However, considerable development is still required in the treatment of nuclear reactions, diffusion and convective mixing.
287 citations
TL;DR: The stellar evolution code YREC as discussed by the authors has been extensively used for other astrophysical applica- tions, some of which are briefly mentioned at the end of the paper, and the procedure for calculating calibrated solar and stellar models is described.
Abstract: Received: date / Accepted: date Abstract The stellar evolution code YREC is outlined with emphasis on its applications to helio- and asteroseismology. The procedure for calculating calibrated solar and stellar models is described. Other features of the code such as a non-local treatment of convective core overshoot, and the implementation of a parametrized description of turbulence in stellar models, are considered in some detail. The code has been extensively used for other astrophysical applica- tions, some of which are briefly mentioned at the end of the paper.
230 citations
TL;DR: CLES as mentioned in this paper is an evolution code recently developed to produce stellar models meeting the specific requirements of studies in asteroseismology, it offers the users a lot of choices in the input physics they want in their models and its versatility allows them to tailor the code to their needs and implement easily new features.
Abstract: CLES is an evolution code recently developed to produce stellar models meeting the specific requirements of studies in asteroseismology. It offers the users a lot of choices in the input physics they want in their models and its versatility allows them to tailor the code to their needs and implement easily new features. We describe the features implemented in the current version of the code and the techniques used to solve the equations of stellar structure and evolution. A brief account is given of the use of the program and of a solar calibration realized with it.
202 citations
TL;DR: The cesam code as discussed by the authors is a set of programs and routines which perform calculations of 1D quasi-hydrostatic stellar evolution including microscopic diffusion of chemical species and diffusion of angular momentum.
Abstract: The cesam code is a consistent set of programs and routines which perform calculations of 1D quasi-hydrostatic stellar evolution including microscopic diffusion of chemical species and diffusion of angular momentum. The solution of the quasi-static equilibrium is performed by a collocation method based on piecewise polynomials approximations projected on a B-spline basis; that allows stable and robust calculations, and the exact restitution of the solution, not only at grid points, even for the discontinuous variables. Other advantages are the monitoring by only one parameter of the accuracy and its improvement by super-convergence. An automatic mesh refinement has been designed for adjusting the localisations of grid points according to the changes of unknowns. For standard models, the evolution of the chemical composition is solved by stiffly stable schemes of orders up to four; in the convection zones mixing and evolution of chemical are simultaneous. The solution of the diffusion equation employs the Galerkin finite elements scheme; the mixing of chemicals is then performed by a strong turbulent diffusion. A precise restoration of the atmosphere is allowed for.
191 citations
TL;DR: In this paper, the propagation of small but finite amplitude ion acoustic solitons and double layers was investigated in electron-positron-ion plasmas in presence of highly negatively charged impurities or dust.
Abstract: Propagation of small but finite amplitude ion acoustic solitons and double layers are investigated in electron–positron–ion plasmas in presence of highly negatively charged impurities or dust. The presence of negatively charged dust particulates can result in existence of two critical concentrations of ion–electron density ratio α. One of them α
D
decides the existence of double layers, whereas the other one α
R
decides the nature of the solitons and double layers. The system supports both compressive and rarefactive solitons as well as double layers. The parameter regimes of transitions from compressive to rarefactive solitons and double layers are also specified.
148 citations
TL;DR: The Liège Oscillation code can be used as a stand-alone program or as a library of subroutines that the user calls from a Fortran main program of his own to compute radial and nonradial adiabatic oscillations of stellar models.
Abstract: The Liege Oscillation code can be used as a stand-alone program or as a library of subroutines that the user calls from a Fortran main program of his own to com- pute radial and nonradial adiabatic oscillations of stellar models. We describe the variables and the equations used by the program and the methods used to solve them. A brief account is given of the use and the output of the program.
141 citations
INAF1
TL;DR: In this paper, the main physical assumptions and numerical procedures adopted by the FRANEC code to compute stellar models in all the evolutionary phases at hydrostatic and thermal equilibrium are summarized.
Abstract: We summarize the main physical assumptions and numerical procedures adopted by the FRANEC code to compute stellar models in all the evolutionary phases at hydrostatic and thermal equilibrium. An application to the Standard Solar Model is also briefly presented.
129 citations
INAF1
TL;DR: The ATON 3.1 evolutionary code as mentioned in this paper was developed for follow up asteroseismology applications, and it includes rotational evolution and a number of other interesting features for follow-up applications.
Abstract: We describe the main features of the evolutionary code ATON 3.1 and its latest version, particularly deviced to be apt for follow up asteroseismology applications. An older version of the code including rotational evolution is also shortly described.
TL;DR: In this paper, the amplitude and period of the present cycle 23 and future fifteen solar cycles were predicted using an autoregressive model, and the predicted period and amplitude of the current cycle 23 were almost similar to the observed cycle.
Abstract: In the previous study (Hiremath, Astron. Astrophys. 452:591, 2006a), the solar cycle is modeled as a forced and damped harmonic oscillator and from all the 22 cycles (1755–1996), long-term amplitudes, frequencies, phases and decay factor are obtained. Using these physical parameters of the previous 22 solar cycles and by an autoregressive model, we predict the amplitude and period of the present cycle 23 and future fifteen solar cycles. The period of present solar cycle 23 is estimated to be 11.73 years and it is expected that onset of next sunspot activity cycle 24 might starts during the period 2008.57±0.17 (i.e., around May–September 2008). The predicted period and amplitude of the present cycle 23 are almost similar to the period and amplitude of the observed cycle. With these encouraging results, we also predict the profiles of future 15 solar cycles. Important predictions are: (i) the period and amplitude of the cycle 24 are 9.34 years and 110 (±11), (ii) the period and amplitude of the cycle 25 are 12.49 years and 110 (±11), (iii) during the cycles 26 (2030–2042 AD), 27 (2042–2054 AD), 34 (2118–2127 AD), 37 (2152–2163 AD) and 38 (2163–2176 AD), the sun might experience a very high sunspot activity, (iv) the sun might also experience a very low (around 60) sunspot activity during cycle 31 (2089–2100 AD) and, (v) length of the solar cycles vary from 8.65 years for the cycle 33 to maximum of 13.07 years for the cycle 35.
TL;DR: In this article, the effect of the coupling between matter and dilaton when the potential of dilaton field is taken as the Mexican hat form is investigated, and the evolving trajectory of the model in the r−s diagram is quite different from those of other dark energy models.
Abstract: Statefinder diagnostic is a useful method which can differ one dark energy model from the others. The Statefinder pair {r,s} is algebraically related to the equation of state of dark energy and its first time derivative. We apply in this paper this method to the dilaton dark energy model based on Weyl-Scaled induced gravitational theory. We investigate the effect of the coupling between matter and dilaton when the potential of dilaton field is taken as the Mexican hat form. We find that the evolving trajectory of our model in the r−s diagram is quite different from those of other dark energy models.
TL;DR: The law of variation for the generalized mean Hubble's parameter in the case of a spatially homogeneous and anisotropic Bianchi type-V space-time metric that yields a constant value of deceleration parameter, is presented in this article.
Abstract: The law of variation for the generalized mean Hubble’s parameter in the case of a spatially homogeneous and anisotropic Bianchi type-V space-time metric that yields a constant value of deceleration parameter, is presented The variation for Hubble’s parameter generates two types of solutions for the average scale factor one is of power-law type and second is of the exponential form Using these two forms, Einstein’s field equations for perfect fluid Bianchi type-V models are solved separately that correspond to singular and non-singular models respectively We find that the constant value of deceleration parameter is reasonable for description of the present day universe We also find that the universe decelerates for positive value of deceleration parameter where as it accelerates for negative one The behaviors of observationally important parameters such as expansion scalar, mean anisotropic parameter and shear scalar are discussed Exact expressions for look-back time, luminosity distance and event horizon versus redshift are derived and their significances are discussed in detail It has been observed that the solutions are compatible with the results of recent observations
TL;DR: In this article, the periodic orbits around the triangular equilibrium points for 0 <μ <μc, where μc is the critical mass value, under the combined influence of small perturbations in the Coriolis and the centrifugal forces respectively, together with the effects of oblateness and radiation pressures of the primaries were investigated.
Abstract: This paper investigates the periodic orbits around the triangular equilibrium points for 0<μ<μc, where μc is the critical mass value, under the combined influence of small perturbations in the Coriolis and the centrifugal forces respectively, together with the effects of oblateness and radiation pressures of the primaries. It is found that the perturbing forces affect the period, orientation and the eccentricities of the long and short periodic orbits.
TL;DR: In this paper, a four-component dusty plasma consisting of electrons, ions, and negative as well as positive dust particles has been considered and the basic features of shock waves that may exist in such a four component dusty plasma have been theoretically investigated by the reductive perturbation method.
Abstract: A four-component dusty plasma consisting of electrons, ions, and negative as well as positive dust particles has been considered. The basic features of shock waves that may exist in such a four-component dusty plasma have been theoretically investigated by the reductive perturbation method. The implications of our results in different regions of space (viz. cometary tails, mesosphere, Jupiter’s magnetosphere, etc.) are briefly discussed.
TL;DR: In this article, exact Bianchi type II, VIII and IX string cosmological models were obtained in the Saez-Ballester theory of gravitation and some physical and geometrical properties of the models were studied.
Abstract: Exact Bianchi type II, VIII and IX String cosmological models are obtained in the Saez-Ballester theory of gravitation. Some physical and geometrical properties of the models are studied.
TL;DR: In this article, the authors considered the photogravitational Chermnykh's problem with the bigger primary as a source of radiation and the small primary as an oblate spheroid.
Abstract: The equilibrium points and their linear stability has been discussed in the generalized photogravitational Chermnykh’s problem. The bigger primary is being considered as a source of radiation and small primary as an oblate spheroid. The effect of radiation pressure has been discussed numerically. The collinear points are linearly unstable and triangular points are stable in the sense of Lyapunov stability provided μ<μ Routh =0.0385201. The effect of gravitational potential from the belt is also examined. The mathematical properties of this system are different from the classical restricted three body problem.
TL;DR: An exact Bianchi type-V perfect fluid cosmological model is obtained in a scalar tensor theory proposed by Sen (Z. Phys. 149:311, 1957) based on Lyra Manifold in case of β is a constant.
Abstract: An exact Bianchi type-V perfect fluid cosmological model is obtained in a scalar tensor theory proposed by Sen (Z. Phys. 149:311, 1957) based on Lyra Manifold in case of β is a constant and it is shown that this cosmological model exists only in the case of Radiation Universe (ρ=3p) if β is a function of ‘t’ using negative constant deceleration parameter. Some physical and geometrical properties of these models are discussed.
TL;DR: The Toulouse–Geneva Evolution Code (TGEC) is presented at its present stage in the framework of the CoRoT-ESTA.
Abstract: In the framework of the CoRoT-ESTA, we present the Toulouse–Geneva Evolution Code (TGEC) at its present stage.
TL;DR: In this article, the effect of solar radiation pressure on the location and stability of the five Lagrangian points is studied, within the frame of elliptic restricted three-body problem, where the primaries are the Sun and Jupiter acting on a particle of negligible mass.
Abstract: In this paper the effect of solar radiation pressure on the location and stability of the five Lagrangian points is studied, within the frame of elliptic restricted three-body problem, where the primaries are the Sun and Jupiter acting on a particle of negligible mass. We found that the radiation pressure plays the rule of slightly reducing the effective mass of the Sun and changes the location of the Lagrangian points. New formulas for the location of the collinear libration points were derived. For large values of the force ratio β, we found that at β=0.12, the collinear point L3 is stable and some families of periodic orbits can be drawn around it.
TL;DR: In this paper, a generalized form of the fractional kinetic equation involving the G-function, a generalized function for fractional calculus, was developed for the computation of the change of chemical composition in stars like the Sun.
Abstract: In view of the usefulness and a great importance of the kinetic equation in certain astrophysical problems the authors develop a new and further generalized form of the fractional kinetic equation involving the G-function, a generalized function for the fractional calculus. This new generalization can be used for the computation of the change of chemical composition in stars like the Sun. The Mellin-Barnes contour integral representation of the G-function is also established. The manifold generality of the G-function is discussed in terms of the solution of the above fractional kinetic equation. A compact and easily computable solution is established. Special cases, involving the generalized Mittag-leffler function and the R-function, are considered. The obtained results imply more precisely the known results.
TL;DR: In this article, the authors conducted an extragalactic CO(3-2) imaging survey of nearby spiral galaxies using the Atacama Submillimeter Telescope Experiment (ASTE).
Abstract: Dense molecular medium plays essential roles in galaxies. As demonstrated by the tight and linear correlation between HCN(1–0) and FIR luminosities among star-forming galaxies, from very nearby to high-z ones, the observation of a dense molecular component is indispensable to understand the star formation laws in galaxies. In order to obtain a general picture of the global distributions of dense molecular medium in normal star-forming galaxies, we have conducted an extragalactic CO(3–2) imaging survey of nearby spiral galaxies using the Atacama Submillimeter Telescope Experiment (ASTE). From the survey (ADIoS; ASTE Dense gas Imaging of Star-forming galaxies), CO(3–2) images of M 83 and NGC 986 are presented. Emphasis is placed on the correlation between the CO(3–2)/CO(1–0) ratio and the star formation efficiency in galaxies. In the central regions of some active galaxies, on the other hand, we often find enhanced or overluminous HCN(1–0) emission. The HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) intensities are often enhanced up to ∼0.2–0.3 and ∼2–3, respectively. Such elevated ratios have never been observed in the nuclear starburst regions. One possible explanation for these high HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) ratios is X-ray induced chemistry in X-ray dominated regions (XDRs), i.e., the overabundance of the HCN molecule in the X-ray irradiated dense molecular tori. If this view is true, the known tight correlation between HCN(1–0) and the star-formation rate breaks in the vicinity of active nuclei. Although the interpretation of these ratios is still an open question, these ratios have a great potential for a new diagnostic tool for the energy sources of dusty galaxies in the ALMA era because these molecular lines are free from dust extinction.
TL;DR: The Atacama Large Millimeter/Submillimeter Array (ALMA) as discussed by the authors is an international millimeter-wavelength radio telescope under construction in Chile, which provides excellent atmospheric transmission over the instrument wavelength range of 0.3 to 3mm.
Abstract: The Atacama Large Millimeter/Submillimeter Array (ALMA) is an international millimeter-wavelength radio telescope under construction in the Atacama Desert of northern Chile. ALMA will be situated on a high-altitude site at 5000 m elevation which provides excellent atmospheric transmission over the instrument wavelength range of 0.3 to 3 mm. ALMA will be comprised of two key observing components—a main array of up to sixty-four 12-m diameter antennas arranged in a multiple configurations ranging in size from 0.15 to ∼18 km, and a set of four 12-m and twelve 7-m antennas operating in a compact array ∼50 m in diameter (known as the Atacama Compact Array, or ACA), providing both interferometric and total-power astronomical information. High-sensitivity dual-polarization 8 GHz-bandwidth spectral-line and continuum measurements between all antennas will be available from two flexible digital correlators.
At the shortest planned wavelength and largest configuration, the angular resolution of ALMA will be 0.005″. The instrument will use superconducting (SIS) mixers to provide the lowest possible receiver noise contribution, and special-purpose water vapor radiometers to assist in calibration of atmospheric phase distortions. A complex optical fiber network will transmit the digitized astronomical signals from the antennas to the correlators in the Array Operations Site Technical Building, and post-correlation to the lower-altitude Operations Support Facility where the array will be controlled, and initial construction and maintenance of the instrument will occur. ALMA Regional Centers in the US, Europe, Japan and Chile will provide the scientific portals for the use of ALMA; early science observations are expected in 2010, with full operations in 2012.
TL;DR: In this paper, the phenomenological decay of Λ has been investigated in the presence of perfect fluid for Bianchi type-I space-time, and the physical significance of the cosmological models has also been discussed.
Abstract: Einstein’s field equations with variable gravitational and cosmological “constant” are considered in presence of perfect fluid for Bianchi type-I space-time. Consequences of the four cases of the phenomenological decay of Λ have been discussed which are consistent with observations. The physical significance of the cosmological models have also been discussed.
TL;DR: In this paper, the authors compare stellar models produced by different stellar evolution codes for the CoRoT/ESTA project, comparing their global quantities, their physical structure, and their oscillation properties.
Abstract: We compare stellar models produced by different stellar evolution codes for the CoRoT/ESTA project, comparing their global quantities, their physical structure, and their oscillation properties. We discuss the differences between models and identify the underlying reasons for these differences. The stellar models are representative of potential CoRoT targets. Overall we find very good agreement between the five different codes, but with some significant deviations. We find noticeable discrepancies (though still at the per cent level) that result from the handling of the equation of state, of the opacities and of the convective boundaries. The results of our work will be helpful in interpreting future asteroseismology results from CoRoT.
TL;DR: The Centurion-18 (C18) as mentioned in this paper is a 0.46m CCD camera that operates from a small dome and is equipped with a large-format camera.
Abstract: We describe the second telescope of the Wise Observatory, a 0.46-m Centurion 18 (C18) installed in 2005, which enhances significantly the observing possibilities. The telescope operates from a small dome and is equipped with a large-format CCD camera. In the last two years this telescope was intensively used in a variety of monitoring projects. The operation of the C18 is now automatic, requiring only start-up at the beginning of a night and close-down at dawn. The observations are mostly performed remotely from the Tel Aviv campus or even from the observer’s home. The entire facility was erected for a component cost of about 70k$ and a labor investment of a total of one man-year. We describe three types of projects undertaken with this new facility: the measurement of asteroid light variability with the purpose of determining physical parameters and binarity, the following-up of transiting extrasolar planets, and the study of AGN variability. The successful implementation of the C18 demonstrates the viability of small telescopes in an age of huge light-collectors, provided the operation of such facilities is very efficient.
TL;DR: In this paper, the authors compared the frequency differences between the seismic codes used to calculate the eigenfrequencies to be finally compared with observations and found that the frequency difference was mainly due to the use of different numerical integration schemes.
Abstract: In order to make asteroseismology a powerful tool to explore stellar interiors, different numerical codes should give the same oscillation frequencies for the same input physics. Any differences found when comparing the numerical values of the eigenfrequencies will be an important piece of information regarding the numerical structure of the code. The ESTA group was created to analyze the non-physical sources of these differences. The work presented in this report is a part of Task 2 of the ESTA group. Basically the work is devoted to test, compare and, if needed, optimize the seismic codes used to calculate the eigenfrequencies to be finally compared with observations. The first step in this comparison is presented here. The oscillation codes of nine research groups in the field have been used in this study. The same physics has been imposed for all the codes in order to isolate the non-physical dependence of any possible difference. Two equilibrium models with different grids, 2172 and 4042 mesh points, have been used, and the latter model includes an explicit modelling of semiconvection just outside the convective core. Comparing the results for these two models illustrates the effect of the number of mesh points and their distribution in particularly critical parts of the model, such as the steep composition gradient outside the convective core. A comprehensive study of the frequency differences found for the different codes is given as well. These differences are mainly due to the use of different numerical integration schemes. The number of mesh points and their distribution are crucial for interpreting the results. The use of a second-order integration scheme plus a Richardson extrapolation provides similar results to a fourth-order integration scheme. The proper numerical description of the Brunt-Vaisala frequency in the equilibrium model is also critical for some modes. This influence depends on the set of the eigenfunctions used for the solution of the differential equations. An unexpected result of this study is the high sensitivity of the frequency differences to the inconsistent use of values of the gravitational constant (G) in the oscillation codes, within the range of the experimentally determined ones, which differ from the value used to compute the equilibrium model. This effect can provide differences for a given equilibrium model substantially larger than those resulting from the use of different codes or numerical techniques; the actual differences between the values of G used by the different codes account for much of the frequency differences found here.
TL;DR: In this paper, two particular examples of such disks around AB Aurigae and HD 142527 are discussed, with an emphasis on results obtained using the Submillimeter Array.
Abstract: Protoplanetary disks are the most probable sites where planet formation takes place. According to theory, planet formation in protoplanetary disks should show remarkable signatures, such as a gap/hole or a spiral structure. In fact, recent high-angular and high-sensitivity observations in millimeter and submillimeter wavelengths, as well as optical/near-IR wavelengths, have shown such structures in protoplanetary disks. Two particular examples of such disks around AB Aurigae and HD 142527 are discussed here, with an emphasis on results obtained using the Submillimeter Array. These disks—and their probable planet formation—will be very important future targets for ALMA to study the physical process of planet formation in detail.
TL;DR: In this paper, high angular resolution mm-wave observations of the Orion-KL region, made with the IRAM Plateau de Bure interferometer (PdBI), reveal the presence of several cores of size 103 AU, which have distinct spectral signatures.
Abstract: High angular resolution mm-wave observations of the Orion-KL region, made with the IRAM Plateau de Bure interferometer (PdBI), reveal the presence of several cores of size 103 AU, which have distinct spectral signatures. Complex molecules such as ethanol, vinyl cyanide and dimethyl ether show different distributions and their relative abundance varies from core to core by orders of magnitude. The molecular column densities derived in the cores also differ widely from the beam-averaged column densities observed with large single-dish telescopes. Obviously, the predictions of hot core chemistry models must be checked against high resolution observations. ALMA, which allies sensitivity and high angular resolution, will be a key instrument for this type of studies.