arXiv subjects

Ali Taani

Publications and source records attributed to Ali Taani.

26 records · Page 2Linked to original sources

arXiv2019

Evolution of Accreting Binary Systems on the Spin-up Line

The measured characteristics of binary pulsars provide valuable insights into the evolution of these systems. We study the aspects of binary evolution particularly relevant to binary Millisecond Pulsars (MSPs), and the formation of close binaries involving degenerate stars through a spin-evolution diagram (spin-up line). For this task, we use a wide variety of binaries, including those with compact components that observed in different energy bands, which we analyze them according to the spin-up line. Their formation and evolution over timescales of binary evolution models are investigated in order to grab any constraint on their evolution, and to estimate the masses of neutron stars with different mass-transfer histories.

astro-ph.HE↗

arXiv2019

Probing the Accretion Induced Collapse of White Dwarfs in Millisecond Pulsars

This paper investigates the progenitors of Millisecond Pulsars (MSPs) with a distribution of long orbital periods (P_orb > 2 d), to show the link between white dwarf (WD) binaries and long orbits for some binary MSPs through the Accretion Induced Collapse (AIC) of a WD. For this purpose, a model is presented to turn binary MSPs into wide binaries and highly circular orbits (e < 0.1) through the asymmetric kick imparted to the pulsar during the AIC process, which may indicate a sizeable kick velocity along the rotation of the proto-neutron star. The results show the effects of shock wave, binding energy, and mass loss (0.2M_sun). The model shows the pulsar systems are relevant to AIC-candidates.

astro-ph.HE↗

arXiv2018

Dynamical Monte Carlo Simulations of 3-D Galactic Systems in Axisymmetric and Triaxial Potentials

We describe the dynamical behavior of isolated old (> 1 G yr) objects-like Neutron Stars (NSs). These isolated NSs are evolved under smooth, time-independent, 3-D gravitational potentials, axisymmetric and with a triaxial dark halo. We analysed the geometry of the dynamics and applied the Poincare section method for comparing the influence of different birth velocity distributions. The inspection of the maximal asymptotic Lyapunov (Lambda) exponent shows that the dynamical behaviors of the selected orbits are nearly the same as the regular orbits with two degrees of freedom, both in axisymmetric and triaxial when (phi, q_z)= (0,0). Conversely, a few chaotic trajectories are found with a rotated triaxial halo when (phi, q_z)= (90, 1.5). The tube orbits preserve the direction of their circulation around either the long or short axis as appeared in the triaxial potential, even when every initial condition leads to different orientations. The Poincare section method shows that there are 2-D invariant tori and invariant curves (islands) around stable periodic orbits that bound to the surface of 3-D tori. The regularity of the several prototypical orbits offer the means to identify the phase space regions with localized motions and to determine their environment in different models, because they can occupy significant parts of phase-space depending on the potential. This is of particular importance in Galactic Dynamics.

astro-ph.HE↗

arXiv2018

On the possibility of disk-fed formation in supergiant high-mass X-ray binaries

We have considered the existence of neutron star magnetic field given by the cyclotron lines. We collected the data of 9 sources of high-mass X-ray binaries with supergiant companions as a case of testing our model, to demonstrate their distribution and evolution. The wind velocity, spin period and magnetic field strength are studied under different mass loss rate. In our model, correlations between mass-loss rate and wind velocity are found and can be tested in further observations. We examined the parameter space where wind accretion is allowed, avoiding barrier of rotating magnetic fields, with robust data of magnetic field of neutron stars. Our model shows that most of sources (6 of 9 systems) can be fed by the wind with relatively slow velocity, and this result is consistent with previous predictions. In a few sources, our model cannot fit under the standard wind accretion scenario. In these peculiar cases, other scenarios (disk formation, partial Roche lobe overflow) should be considered. This would provide information about the evolutionary tracks of various types of binaries, and thus show a clear dichotomy behavior in wind-fed X-ray binary systems.

astro-ph.HE↗

arXiv2017

Quiescent photometric modulations of two low-inclination cataclysmic variables KZGem and TWVir

The quiescent periodic photometric modulations of two low-inclination cataclysmic variables observed in Kepler K2 Campaigns 0 and 1, KZ Gem and TW Vir, are investigated. A phase-correcting method was successfully used to detect the orbital modulations of KZ Gem and TW Vir and improve their orbital periods. The light curve morphologies of both CVs were further analyzed by defining flux ratios and creating colormaps. KZ Gem shows ellipsoidal modulations with an orbital period of 0.22242(1) day, twice the period listed in the updated RK catalogue (Edition 7.24). With this newly determined period, KZ Gem is no longer a CV in the period gap, but a long-period CV. A part of the quiescent light curve of TW Vir that had the highest stability was used to deduce its improved orbital period of 0.182682(3) day. The flat patterns shown in the colormaps of the flux ratios for KZ Gem demonstrate the stability of their orbital modulations, while TW Vir show variable orbital modulations during the K2 datasets. In TW Vir, the single versus double-peaked nature of the quiescent orbital variations before and after superoutburst may be related to the effect of the superoutburst on the accretion disk.

astro-ph.SR↗

arXiv2012

Modeling the Spatial Distribution of Neutron Stars in the Galaxy

In this paper we investigate the space and velocity distributions of old neutron stars (aged 109 to 1010 yr) in our Galaxy. Galactic old Neutron Stars (NSs) population fills a torus-like area extending to a few tens kiloparsecs above the galactic plane. The initial velocity distribution of NSs is not well known, in this work we adopt a three component initial distribution, as given by the contribution of kick velocities, circular velocities and Maxwellian velocities. For the spatial initial distribution we use a Gamma function. We then use Monte Carlo simulations to follow the evolution of the NSs under the influence of the Paczy¶nski Galactic gravitational potential. Our calculations show that NS orbits have a very large Galactic radial expansion and that their radial distribution peak is quite close to their progenitors' one. We also study the NS vertical distribution and find that it can well be described by a double exponential low. Finally, we investigate the correlation of the vertical and radial distribution and study the radial dependence of scale-heights.

astro-ph.HE↗

arXiv2012

Investigation of Some Physical Properties of Accretion Induced Collapse in Producing Millisecond Pulsars

We investigate some physical characteristics of Millisecond Pulsar (MSP) such as magnetic fields, spin periods and masses, that are produced by Accretion Induced Collapse (AIC) of an accreting white dwarf (WD) in stellar binary systems. We also investigate the changes of these characteristics during the mass-transfer phase of the system in its way to become a MSP. Our approach allows us to follow the changes in magnetic fields and spin periods during the conversion of WDs to MSPs via AIC process. We focus our attention mainly on the massive binary WDs (M > 1.0Msun) forming cataclysmic variables, that could potentially evolve to reach Chandrasekhar limit, thereafter they collapse and become MSPs. Knowledge about these parameters might be useful for further modeling of the observed features of AIC.

astro-ph.HE↗

arXiv2011

Where do the Progenitors of Millisecond Pulsars come from?

Observations of a large population of Millisecond Pulsars (MSPs) show a wide divergence in the orbital periods (from approximately hours to a few months). In the standard view, Low-Mass X-Ray Binaries (LMXBs) are considered as progenitors for some MSPs during the recycling process. We present a systematic study that combines different types of compact objects in binaries such as Cataclysmic Variables (CVs), LMXBs and MSPs. We plot them together in the so called Corbet diagram. Larger and different samples are needed to better constrain the result as a function of the environment and formations. A scale diagram showing the distribution of MSPs for different orbital periods and the aspects for their progenitors relying on Accretion Induced Collapse (AIC) of white dwarfs in binaries. Thus massive CVs (M >1.1M\odot) can play a vital role on binary evolution, as well as of the physical processes involved in the formation and evolution of neutron stars and their magnetic fields, and could turn into binary MSPs with different scales of orbital periods; this effect can be explained by the AIC process. This scenario also suggests that some fraction of isolated MSPs in the Galactic disk could be formed through the same channel, formingthe contribution of some CVs to the single-degenerate progenitors of Type Ia supernova. Furthermore, we have refined the statistical distribution and evolution by using updated data. This implies that the significant studies of compact objects in binary systems can benefit from the Corbet diagram.

astro-ph.HE↗