GAA - Grup d'Astronomia i Astrofísica
http://hdl.handle.net/2117/1136
Sun, 25 Feb 2018 01:48:57 GMT2018-02-25T01:48:57ZSpectroscopic study of Ne-20 + p reactions using the JENSA gas-jet target to constrain the astrophysical F-18(p, alpha)O-15 rate
http://hdl.handle.net/2117/113576
Spectroscopic study of Ne-20 + p reactions using the JENSA gas-jet target to constrain the astrophysical F-18(p, alpha)O-15 rate
Bardayan, D. W.; Chipps, Kelly A.; Ahn, S.; Blackmon, J. C.; Carmichael, S.; Greife, U.; José Pont, Jordi; Kontos, A.; Matos, Mireya E.; Thompson, Paul
The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas-jet target was used to perform spectroscopic studies of 20Ne+p reactions. Levels in 19Ne were probed via the 20Ne(p,d)19Ne reaction to constrain the astrophysical rate of the 18F(p,a)15O reaction. Additionally, the first spectroscopic study of the 20Ne(p,3He)18F reaction was performed. Angular distribution data were used to determine or confirm the spins of several previously observed levels, and the existence of a strong subthreshold 18F(p,a)15O resonance was verified.
Thu, 01 Feb 2018 14:36:08 GMThttp://hdl.handle.net/2117/1135762018-02-01T14:36:08ZBardayan, D. W.Chipps, Kelly A.Ahn, S.Blackmon, J. C.Carmichael, S.Greife, U.José Pont, JordiKontos, A.Matos, Mireya E.Thompson, PaulThe Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas-jet target was used to perform spectroscopic studies of 20Ne+p reactions. Levels in 19Ne were probed via the 20Ne(p,d)19Ne reaction to constrain the astrophysical rate of the 18F(p,a)15O reaction. Additionally, the first spectroscopic study of the 20Ne(p,3He)18F reaction was performed. Angular distribution data were used to determine or confirm the spins of several previously observed levels, and the existence of a strong subthreshold 18F(p,a)15O resonance was verified.The white dwarf binary pathways survey - II. radial velocities of 1453 FGK stars with white dwarf companions from LAMOST DR4
http://hdl.handle.net/2117/113534
The white dwarf binary pathways survey - II. radial velocities of 1453 FGK stars with white dwarf companions from LAMOST DR4
Rebassa Mansergas, Alberto; Ren, J. J.; Irawati, P.; García-Berro Montilla, Enrique; Parsons, S. G.; Schreiber, Mathias R.; Gänsicke, Boris T.; Rodríguez-Gil, Pablo; Liu, X.; Manser, C. J.; Nevado, S.P.; Jiménez Ibarra, Felipe; Costero, R.; Michel, R.; Zorotovic, Mónica; Hollands, M.; Han, Z.; Luo, A.; Hita Villaverde, Enrique F.; Kong, X.
We present the second paper of a series of publications aiming at obtaining a better understanding regarding the nature of type Ia supernovae (SN Ia) progenitors by studying a large sample of detached F, G and K main-sequence stars in close orbits with white dwarf companions (i.e. WD+FGK binaries). We employ the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) data release 4 spectroscopic data base together with Galaxy Evolution Explorer (GALEX) ultraviolet fluxes to identify 1549 WD+FGK binary candidates (1057 of which are new), thus doubling the number of known sources.We measure the radial velocities of 1453 of these binaries from the available LAMOST spectra and/or from spectra obtained by us at a wide variety of different telescopes around the globe. The analysis of the radial velocity data allows us to identify 24 systems displaying more than 3s radial velocity variation that we classify as close binaries. We also discuss the fraction of close binaries among WD+FGK systems, which we find to be ~10 per cent, and demonstrate that high-resolution spectroscopy is required to efficiently identify double-degenerate SNIa progenitor candidates.
Thu, 01 Feb 2018 10:55:16 GMThttp://hdl.handle.net/2117/1135342018-02-01T10:55:16ZRebassa Mansergas, AlbertoRen, J. J.Irawati, P.García-Berro Montilla, EnriqueParsons, S. G.Schreiber, Mathias R.Gänsicke, Boris T.Rodríguez-Gil, PabloLiu, X.Manser, C. J.Nevado, S.P.Jiménez Ibarra, FelipeCostero, R.Michel, R.Zorotovic, MónicaHollands, M.Han, Z.Luo, A.Hita Villaverde, Enrique F.Kong, X.We present the second paper of a series of publications aiming at obtaining a better understanding regarding the nature of type Ia supernovae (SN Ia) progenitors by studying a large sample of detached F, G and K main-sequence stars in close orbits with white dwarf companions (i.e. WD+FGK binaries). We employ the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) data release 4 spectroscopic data base together with Galaxy Evolution Explorer (GALEX) ultraviolet fluxes to identify 1549 WD+FGK binary candidates (1057 of which are new), thus doubling the number of known sources.We measure the radial velocities of 1453 of these binaries from the available LAMOST spectra and/or from spectra obtained by us at a wide variety of different telescopes around the globe. The analysis of the radial velocity data allows us to identify 24 systems displaying more than 3s radial velocity variation that we classify as close binaries. We also discuss the fraction of close binaries among WD+FGK systems, which we find to be ~10 per cent, and demonstrate that high-resolution spectroscopy is required to efficiently identify double-degenerate SNIa progenitor candidates.Testing the white dwarf mass-radius relationship with eclipsing binaries
http://hdl.handle.net/2117/113341
Testing the white dwarf mass-radius relationship with eclipsing binaries
Parsons, S. G.; Gänsicke, Boris T.; Marsh, T. R.; Ashley, R. P.; Bours, M. C. P.; Breedt, E.; Burleigh, M. R.; Copperwheat, C. M.; Dhillon, V. S.; Green, M.; Hardy, L. K.; Hermes, J. J.; Irawati, P.; Kerry, P.; Littlefair, S. P.; McAllister, M. J.; Rattanasoon, S.; Rebassa Mansergas, Alberto; Sahman, D. I.; Schreiber, Mathias R.
We present high-precision, model-independent, mass and radius measurements for 16 white dwarfs in detached eclipsing binaries and combine these with previously published data to test the theoretical white dwarf mass–radius relationship. We reach a mean precision of 2.4 per cent in mass and 2.7 per cent in radius, with our best measurements reaching a precision of 0.3 per cent in mass and 0.5 per cent in radius. We find excellent agreement between the measured and predicted radii across a wide range of masses and temperatures. We also find the radii of all white dwarfs with masses less than 0.48 M¿ to be fully consistent with helium core models, but they are on average 9 per cent larger than those of carbon–oxygen core models. In contrast, white dwarfs with masses larger than 0.52 M¿ all have radii consistent with carbon–oxygen core models. Moreover, we find that all but one of the white dwarfs in our sample have radii consistent with possessing thick surface hydrogen envelopes (10-5 = MH/MWD = 10-4), implying that the surface hydrogen layers of these white dwarfs are not obviously affected by common envelope evolution.
Mon, 29 Jan 2018 14:05:58 GMThttp://hdl.handle.net/2117/1133412018-01-29T14:05:58ZParsons, S. G.Gänsicke, Boris T.Marsh, T. R.Ashley, R. P.Bours, M. C. P.Breedt, E.Burleigh, M. R.Copperwheat, C. M.Dhillon, V. S.Green, M.Hardy, L. K.Hermes, J. J.Irawati, P.Kerry, P.Littlefair, S. P.McAllister, M. J.Rattanasoon, S.Rebassa Mansergas, AlbertoSahman, D. I.Schreiber, Mathias R.We present high-precision, model-independent, mass and radius measurements for 16 white dwarfs in detached eclipsing binaries and combine these with previously published data to test the theoretical white dwarf mass–radius relationship. We reach a mean precision of 2.4 per cent in mass and 2.7 per cent in radius, with our best measurements reaching a precision of 0.3 per cent in mass and 0.5 per cent in radius. We find excellent agreement between the measured and predicted radii across a wide range of masses and temperatures. We also find the radii of all white dwarfs with masses less than 0.48 M¿ to be fully consistent with helium core models, but they are on average 9 per cent larger than those of carbon–oxygen core models. In contrast, white dwarfs with masses larger than 0.52 M¿ all have radii consistent with carbon–oxygen core models. Moreover, we find that all but one of the white dwarfs in our sample have radii consistent with possessing thick surface hydrogen envelopes (10-5 = MH/MWD = 10-4), implying that the surface hydrogen layers of these white dwarfs are not obviously affected by common envelope evolution.The kinematics of the white dwarf population from the SDSS DR12
http://hdl.handle.net/2117/112856
The kinematics of the white dwarf population from the SDSS DR12
Anguiano, B.; Rebassa Mansergas, Alberto; García-Berro Montilla, Enrique; Torres Gil, Santiago; Freeman, K. C.; Zwitter, T.
We use the Sloan Digital Sky Survey Data Release 12, which is the largest available white dwarf catalogue to date, to study the evolution of the kinematical properties of the population of white dwarfs in the Galactic disc. We derive masses, ages, photometric distances and radial velocities for all white dwarfs with hydrogen-rich atmospheres. For those stars for which proper motions from the USNO-B1 catalogue are available, the true three-dimensional components of the stellar space velocity are obtained. This subset of the original sample comprises 20 247 objects, making it the largest sample of white dwarfs with measured three-dimensional velocities. Furthermore, the volume probed by our sample is large, allowing us to obtain relevant kinematical information. In particular, our sample extends from a Galactocentric radial distance RG = 7.8 to 9.3 kpc, and vertical distances from the Galactic plane ranging from Z = -0.5 to 0.5 kpc. We examine the mean components of the stellar three-dimensional velocities, as well as their dispersions with respect to the Galactocentric and vertical distances. We confirm the existence of a mean Galactocentric radial velocity gradient, ¿<VR>/¿RG = -3 ± 5 km s-1 kpc-1. We also confirm north–south differences in <Vz>. Specifically, we find that white dwarfs with Z > 0 (in the North Galactic hemisphere) have <Vz> < 0, while the reverse is true for white dwarfs with Z < 0. The age–velocity dispersion relation derived from the present sample indicates that the Galactic population of white dwarfs may have experienced an additional source of heating, which adds to the secular evolution of the Galactic disc.
This is a pre-copyedited, author-produced PDF of an article accepted for publication in "Monthly Notices of the Royal Astronomical Society" following peer review. The version of record [Monthly Notices of the Royal Astronomical Society, Volume 469, Issue 2, 1 August 2017, Pages 2102–2120, https://doi.org/10.1093/mnras/stx796] is available online at: https://academic.oup.com/mnras/article/469/2/2102/3749527.
Tue, 16 Jan 2018 15:57:02 GMThttp://hdl.handle.net/2117/1128562018-01-16T15:57:02ZAnguiano, B.Rebassa Mansergas, AlbertoGarcía-Berro Montilla, EnriqueTorres Gil, SantiagoFreeman, K. C.Zwitter, T.We use the Sloan Digital Sky Survey Data Release 12, which is the largest available white dwarf catalogue to date, to study the evolution of the kinematical properties of the population of white dwarfs in the Galactic disc. We derive masses, ages, photometric distances and radial velocities for all white dwarfs with hydrogen-rich atmospheres. For those stars for which proper motions from the USNO-B1 catalogue are available, the true three-dimensional components of the stellar space velocity are obtained. This subset of the original sample comprises 20 247 objects, making it the largest sample of white dwarfs with measured three-dimensional velocities. Furthermore, the volume probed by our sample is large, allowing us to obtain relevant kinematical information. In particular, our sample extends from a Galactocentric radial distance RG = 7.8 to 9.3 kpc, and vertical distances from the Galactic plane ranging from Z = -0.5 to 0.5 kpc. We examine the mean components of the stellar three-dimensional velocities, as well as their dispersions with respect to the Galactocentric and vertical distances. We confirm the existence of a mean Galactocentric radial velocity gradient, ¿<VR>/¿RG = -3 ± 5 km s-1 kpc-1. We also confirm north–south differences in <Vz>. Specifically, we find that white dwarfs with Z > 0 (in the North Galactic hemisphere) have <Vz> < 0, while the reverse is true for white dwarfs with Z < 0. The age–velocity dispersion relation derived from the present sample indicates that the Galactic population of white dwarfs may have experienced an additional source of heating, which adds to the secular evolution of the Galactic disc.One-armed spiral instability in double-degenerate post-merger accretion disks
http://hdl.handle.net/2117/112350
One-armed spiral instability in double-degenerate post-merger accretion disks
kashyap, Rahul; Fisher, Robert T.; García-Berro Montilla, Enrique; Aznar-Siguán, Gabriela; Ji, Suoqing; Loren Aguilar, Pablo
Increasing observational and theoretical evidence points to binary white dwarf (WD) mergers as the origin of some, if not most, normal Type Ia supernovae (SNe Ia). In this paper, we discuss the post-merger evolution of binary WD mergers and their relevance to the double-degenerate channel of SNe Ia. We present 3D simulations of carbon–oxygen (C/O) WD binary systems undergoing unstable mass transfer, where we vary both the total mass and the mass ratio. We demonstrate that these systems generally give rise to a one-armed gravitational spiral instability. The spiral density modes transport mass and angular momentum in the disk even in the absence of a magnetic field and are most pronounced in systems with secondary-to-primary mass ratios larger than 0.6. We further analyze carbon burning in these systems to assess the possibility of detonation. Unlike the case of a $1.1+1.0\,{M}_{\odot }$ C/O WD binary, we find that WD binary systems with lower mass and smaller mass ratios do not detonate as SNe Ia up to ~8–22 outer dynamical times. Two additional models do, however, undergo net heating, and their secular increase in temperature could possibly result in a detonation on timescales longer than those considered here.
Wed, 20 Dec 2017 22:09:28 GMThttp://hdl.handle.net/2117/1123502017-12-20T22:09:28Zkashyap, RahulFisher, Robert T.García-Berro Montilla, EnriqueAznar-Siguán, GabrielaJi, SuoqingLoren Aguilar, PabloIncreasing observational and theoretical evidence points to binary white dwarf (WD) mergers as the origin of some, if not most, normal Type Ia supernovae (SNe Ia). In this paper, we discuss the post-merger evolution of binary WD mergers and their relevance to the double-degenerate channel of SNe Ia. We present 3D simulations of carbon–oxygen (C/O) WD binary systems undergoing unstable mass transfer, where we vary both the total mass and the mass ratio. We demonstrate that these systems generally give rise to a one-armed gravitational spiral instability. The spiral density modes transport mass and angular momentum in the disk even in the absence of a magnetic field and are most pronounced in systems with secondary-to-primary mass ratios larger than 0.6. We further analyze carbon burning in these systems to assess the possibility of detonation. Unlike the case of a $1.1+1.0\,{M}_{\odot }$ C/O WD binary, we find that WD binary systems with lower mass and smaller mass ratios do not detonate as SNe Ia up to ~8–22 outer dynamical times. Two additional models do, however, undergo net heating, and their secular increase in temperature could possibly result in a detonation on timescales longer than those considered here.SPHYNX: an accurate density-based SPH method for astrophysical applications
http://hdl.handle.net/2117/112180
SPHYNX: an accurate density-based SPH method for astrophysical applications
Cabezon Gomez, Ruben Martin; García Senz, Domingo; Figueira, Joana
Aims. Hydrodynamical instabilities and shocks are ubiquitous in astrophysical scenarios. Therefore, an accurate numerical simulation of these phenomena is mandatory to correctly model and understand many astrophysical events, such as supernovas, stellar collisions, or planetary formation. In this work, we attempt to address many of the problems that a commonly used technique, smoothed particle hydrodynamics (SPH), has when dealing with subsonic hydrodynamical instabilities or shocks. To that aim we built a new SPH code named SPHYNX, that includes many of the recent advances in the SPH technique and some other new ones, which we present here. Methods. SPHYNX is of Newtonian type and grounded in the Euler-Lagrange formulation of the smoothed-particle hydrodynamics technique. Its distinctive features are: the use of an integral approach to estimating the gradients; the use of a flexible family of interpolators called sinc kernels, which suppress pairing instability; and the incorporation of a new type of volume element which provides a better partition of the unity. Unlike other modern formulations, which consider volume elements linked to pressure, our volume element choice relies on density. SPHYNX is, therefore, a density-based SPH code. Results. A novel computational hydrodynamic code oriented to Astrophysical applications is described, discussed, and validated in the following pages. The ensuing code conserves mass, linear and angular momentum, energy, entropy, and preserves kernel normalization even in strong shocks. In our proposal, the estimation of gradients is enhanced using an integral approach. Additionally, we introduce a new family of volume elements which reduce the so-called tensile instability. Both features help to suppress the damp which often prevents the growth of hydrodynamic instabilities in regular SPH codes. Conclusions. On the whole, SPHYNX has passed the verification tests described below. For identical particle setting and initial conditions the results were similar (or better in some particular cases) than those obtained with other SPH schemes such as GADGET-2, PSPH or with the recent density-independent formulation (DISPH) and conservative reproducing kernel (CRKSPH) techniques.
Fri, 15 Dec 2017 13:57:28 GMThttp://hdl.handle.net/2117/1121802017-12-15T13:57:28ZCabezon Gomez, Ruben MartinGarcía Senz, DomingoFigueira, JoanaAims. Hydrodynamical instabilities and shocks are ubiquitous in astrophysical scenarios. Therefore, an accurate numerical simulation of these phenomena is mandatory to correctly model and understand many astrophysical events, such as supernovas, stellar collisions, or planetary formation. In this work, we attempt to address many of the problems that a commonly used technique, smoothed particle hydrodynamics (SPH), has when dealing with subsonic hydrodynamical instabilities or shocks. To that aim we built a new SPH code named SPHYNX, that includes many of the recent advances in the SPH technique and some other new ones, which we present here. Methods. SPHYNX is of Newtonian type and grounded in the Euler-Lagrange formulation of the smoothed-particle hydrodynamics technique. Its distinctive features are: the use of an integral approach to estimating the gradients; the use of a flexible family of interpolators called sinc kernels, which suppress pairing instability; and the incorporation of a new type of volume element which provides a better partition of the unity. Unlike other modern formulations, which consider volume elements linked to pressure, our volume element choice relies on density. SPHYNX is, therefore, a density-based SPH code. Results. A novel computational hydrodynamic code oriented to Astrophysical applications is described, discussed, and validated in the following pages. The ensuing code conserves mass, linear and angular momentum, energy, entropy, and preserves kernel normalization even in strong shocks. In our proposal, the estimation of gradients is enhanced using an integral approach. Additionally, we introduce a new family of volume elements which reduce the so-called tensile instability. Both features help to suppress the damp which often prevents the growth of hydrodynamic instabilities in regular SPH codes. Conclusions. On the whole, SPHYNX has passed the verification tests described below. For identical particle setting and initial conditions the results were similar (or better in some particular cases) than those obtained with other SPH schemes such as GADGET-2, PSPH or with the recent density-independent formulation (DISPH) and conservative reproducing kernel (CRKSPH) techniques.First measurement of the 34S(p,gamma)35Cl reaction rate through indirect methods for presolar nova grains
http://hdl.handle.net/2117/109218
First measurement of the 34S(p,gamma)35Cl reaction rate through indirect methods for presolar nova grains
Gillespie, S; Parikh, A.; Barton, C; Faestermann, Thomas; José Pont, Jordi; Hertenberger, R.; Wirth, Hans Friedrich; de Séréville, N; Riley, J; Williams, M
Sulphur isotopic ratio measurements may help to establish the astrophysical sites in which certain presolar grains were formed. Nova model predictions of the 34S/32S ratio are, however, unreliable due to the lack of an experimental 34S(p,¿)35Cl reaction rate. To this end, we have measured the 34S(3He,d)35Cl reaction at 20 MeV using a high resolution quadrupole-dipole-dipole-dipole magnetic spectrograph. Twenty-two levels over 6.2 MeV <Ex(35Cl)<7.4 MeV were identified, ten of which were previously unobserved. Proton-transfer spectroscopic factors have been measured for the first time over the energy range relevant for novae. With this new spectroscopic information a new 34S(p,¿)35Cl reaction rate has been determined using a Monte Carlo method. Hydrodynamic nova model calculations have been performed using this new reaction rate. These models show that remaining uncertainties in the 34S(p,¿) rate affect nucleosynthesis predictions by less than a factor of 1.4, and predict a 34S/32S isotopic ratio of 0.014–0.017. Since recent type II supernova models predict 34S/32S=0.026-0.053, the 34S/32S isotopic ratio may be used, in conjunction with other isotopic signatures, to distinguish presolar grains from oxygen-neon nova and type II supernova origin. Our results address a key nuclear physics uncertainty on which recent considerations discounting the nova origin of several grains depend.
Wed, 25 Oct 2017 16:39:16 GMThttp://hdl.handle.net/2117/1092182017-10-25T16:39:16ZGillespie, SParikh, A.Barton, CFaestermann, ThomasJosé Pont, JordiHertenberger, R.Wirth, Hans Friedrichde Séréville, NRiley, JWilliams, MSulphur isotopic ratio measurements may help to establish the astrophysical sites in which certain presolar grains were formed. Nova model predictions of the 34S/32S ratio are, however, unreliable due to the lack of an experimental 34S(p,¿)35Cl reaction rate. To this end, we have measured the 34S(3He,d)35Cl reaction at 20 MeV using a high resolution quadrupole-dipole-dipole-dipole magnetic spectrograph. Twenty-two levels over 6.2 MeV <Ex(35Cl)<7.4 MeV were identified, ten of which were previously unobserved. Proton-transfer spectroscopic factors have been measured for the first time over the energy range relevant for novae. With this new spectroscopic information a new 34S(p,¿)35Cl reaction rate has been determined using a Monte Carlo method. Hydrodynamic nova model calculations have been performed using this new reaction rate. These models show that remaining uncertainties in the 34S(p,¿) rate affect nucleosynthesis predictions by less than a factor of 1.4, and predict a 34S/32S isotopic ratio of 0.014–0.017. Since recent type II supernova models predict 34S/32S=0.026-0.053, the 34S/32S isotopic ratio may be used, in conjunction with other isotopic signatures, to distinguish presolar grains from oxygen-neon nova and type II supernova origin. Our results address a key nuclear physics uncertainty on which recent considerations discounting the nova origin of several grains depend.A Trojan horse approach to the production of 18F in Novae
http://hdl.handle.net/2117/109215
A Trojan horse approach to the production of 18F in Novae
la Cognata, M; Pizzone, R; José Pont, Jordi; Hernanz Carbó, Margarita; Cherubini, S; Gulino, M; Rapisarda, G; Spitaleri, C
Crucial information on nova nucleosynthesis can be potentially inferred from ¿-ray signals powered by 18F decay. Therefore, the reaction network producing and destroying this radioactive isotope has been extensively studied in the last years. Among those reactions, the 18F(p, a)15O cross-section has been measured by means of several dedicated experiments, both using direct and indirect methods. The presence of interfering resonances in the energy region of astrophysical interest has been reported by many authors including the recent applications of the Trojan Horse Method. In this work, we evaluate what changes are introduced by the Trojan Horse data in the 18F(p, a)15O astrophysical factor recommended in a recent R-matrix analysis, accounting for existing direct and indirect measurements. Then the updated reaction rate is calculated and parameterized and implications of the new results on nova nucleosynthesis are thoroughly discussed.
Wed, 25 Oct 2017 16:23:24 GMThttp://hdl.handle.net/2117/1092152017-10-25T16:23:24Zla Cognata, MPizzone, RJosé Pont, JordiHernanz Carbó, MargaritaCherubini, SGulino, MRapisarda, GSpitaleri, CCrucial information on nova nucleosynthesis can be potentially inferred from ¿-ray signals powered by 18F decay. Therefore, the reaction network producing and destroying this radioactive isotope has been extensively studied in the last years. Among those reactions, the 18F(p, a)15O cross-section has been measured by means of several dedicated experiments, both using direct and indirect methods. The presence of interfering resonances in the energy region of astrophysical interest has been reported by many authors including the recent applications of the Trojan Horse Method. In this work, we evaluate what changes are introduced by the Trojan Horse data in the 18F(p, a)15O astrophysical factor recommended in a recent R-matrix analysis, accounting for existing direct and indirect measurements. Then the updated reaction rate is calculated and parameterized and implications of the new results on nova nucleosynthesis are thoroughly discussed.An efficient method for the static deflection analysis of an infinite beam on a nonlinear elastic foundation of one-way spring model
http://hdl.handle.net/2117/108739
An efficient method for the static deflection analysis of an infinite beam on a nonlinear elastic foundation of one-way spring model
Ahmad, Fayyaz; Ullah, Malik Zaka; Jang, Taek Soo; Alaidarous, Eman
An efficient numerical iterative method is constructed for the static deflection of an infinite beam on a nonlinear elastic foundation. The proposed iterative scheme consists of quasilinear method (QLM) and Green’s function technique. The QLM translates the nonlinear ordinary differential equation into iterative linear ordinary differential equation. The successive iterations of quasilinear form of ordinary differential equation (ODE) show the quadratic convergence if an initial guess is chosen in the neighbourhood of true solution. The Green’s function technique converts the differential operator into an integral operator and the integral operator is approximated by discrete summation which finally gives us an iterative formula for the resulting set of algebraic equations.The numerical validity and efficiency are proved by simulating some nonlinear problems.
Tue, 17 Oct 2017 08:29:35 GMThttp://hdl.handle.net/2117/1087392017-10-17T08:29:35ZAhmad, FayyazUllah, Malik ZakaJang, Taek SooAlaidarous, EmanAn efficient numerical iterative method is constructed for the static deflection of an infinite beam on a nonlinear elastic foundation. The proposed iterative scheme consists of quasilinear method (QLM) and Green’s function technique. The QLM translates the nonlinear ordinary differential equation into iterative linear ordinary differential equation. The successive iterations of quasilinear form of ordinary differential equation (ODE) show the quadratic convergence if an initial guess is chosen in the neighbourhood of true solution. The Green’s function technique converts the differential operator into an integral operator and the integral operator is approximated by discrete summation which finally gives us an iterative formula for the resulting set of algebraic equations.The numerical validity and efficiency are proved by simulating some nonlinear problems.Updated evolutionary sequences for hydrogen-deficient white dwarfs
http://hdl.handle.net/2117/108520
Updated evolutionary sequences for hydrogen-deficient white dwarfs
Camisassa, Maria E; Althaus, Leandro G.; Rohrmann, René D.; García-Berro Montilla, Enrique; Torres Gil, Santiago; Corsico, Alejandro H.; Wachlin, Felipe C.
We present a set of full evolutionary sequences for white dwarfs with hydrogen-deficient atmospheres. We take into account the evolutionary history of the progenitor stars, all the relevant energy sources involved in the cooling, element diffusion in the very outer layers, and outer boundary conditions provided by new and detailed non-gray white dwarf model atmospheres for pure helium composition. These model atmospheres are based on the most up-to-date physical inputs. Our calculations extend down to very low effective temperatures, of ~2500 K, provide a homogeneous set of evolutionary cooling tracks that are appropriate for mass and age determinations of old hydrogen-deficient white dwarfs, and represent a clear improvement over previous efforts, which were computed using gray atmospheres.
Mon, 09 Oct 2017 12:12:17 GMThttp://hdl.handle.net/2117/1085202017-10-09T12:12:17ZCamisassa, Maria EAlthaus, Leandro G.Rohrmann, René D.García-Berro Montilla, EnriqueTorres Gil, SantiagoCorsico, Alejandro H.Wachlin, Felipe C.We present a set of full evolutionary sequences for white dwarfs with hydrogen-deficient atmospheres. We take into account the evolutionary history of the progenitor stars, all the relevant energy sources involved in the cooling, element diffusion in the very outer layers, and outer boundary conditions provided by new and detailed non-gray white dwarf model atmospheres for pure helium composition. These model atmospheres are based on the most up-to-date physical inputs. Our calculations extend down to very low effective temperatures, of ~2500 K, provide a homogeneous set of evolutionary cooling tracks that are appropriate for mass and age determinations of old hydrogen-deficient white dwarfs, and represent a clear improvement over previous efforts, which were computed using gray atmospheres.