pp 107-119 June 2014
Jagadish Singh Joel John Taura
We have examined the effects of oblateness up to 𝐽_{4} of the less massive primary and gravitational potential from a circum-binary belt on the linear stability of triangular equilibrium points in the circular restricted three-body problem, when the more massive primary emits electromagnetic radiation impinging on the other bodies of the system. Using analytical and numerical methods, we have found the triangular equilibrium points and examined their linear stability. The triangular equilibrium points move towards the line joining the primaries in the presence of any of these perturbations, except in the presence of oblateness up to 𝐽_{4} where the points move away from the line joining the primaries. It is observed that the triangular points are stable for 0 < 𝜇 < 𝜇_{c} and unstable for 𝜇_{c} ≤ 𝜇 ≤ $\frac{1}{2}$, where 𝜇_{c} is the critical mass ratio affected by the oblateness up to 𝐽_{4} of the less massive primary, electromagnetic radiation of the more massive primary and potential from the belt, all of which have destabilizing tendencies, except the coefficient 𝐽_{4} and the potential from the belt. A practical application of this model could be the study of motion of a dust particle near a radiating star and an oblate body surrounded by a belt.
pp 121-141 June 2014
Evolution of the Galaxy and the Birth of the Solar System: The Short-Lived Nuclides Connection
An attempt is made, probably for the first time, to understand the origin of the solar system in context with the evolution of the galaxy as a natural consequence of the birth of several generations of stellar clusters. The galaxy is numerically simulated to deduce the inventories of the short-lived nuclides, ^{26}Al, ^{36}Cl, ^{41}Ca, ^{53}Mn and ^{60}Fe, from the stellar nucleosynthetic contributions of the various stellar clusters using an 𝑁-body simulation with updated prescriptions of the astrophysical processes. The galaxy is evolved by considering the discreteness associated with the stellar clusters and individual stars. We estimate the steady state abundance of the radionuclides around 4.56 billion years ago at the time of formation of the solar system. Further, we also estimate the present ^{26}Al/^{27}Al and ^{60}Fe/^{56}Fe of the interstellar medium that match within a factor of two with the observed estimates. In contrary to the conventional Galactic Chemical Evolution (GCE) model, the present adopted numerical approach provides a natural framework to understand the astrophysical environment related with the origin of the solar system. We deduce the nature of the two stellar clusters; the one that formed and evolved prior to the solar system formation, and the other within which the solar system that was probably formed. The former could have contributed to the short-lived nuclides ^{129}I and ^{53}Mn, whereas, the supernova associated with the most massive star in the latter contributed ^{26}Al and ^{60}Fe to the solar system. The analysiswas performed with the revised solar metallicity of 0.014
pp 143-156 June 2014
Multicolour CCD Photometric Study of Galactic Star Clusters SAI 63 and SAI 75
R. K. S. Yadav S. I. Leonova R. Sagar E. V. Glushkova
We present 𝑈𝐵𝑉𝐼 CCD photometric observations obtained in the field of open clusters SAI 63 and SAI 75. CCD optical data obtained for the first time for these clusters are used to derive the fundamental parameters of the clusters. Stellar surface density profile indicates that radii of SAI 63 and SAI 75 are ∼ 3'.5 and 2'.5 respectively. The reddenings 𝐸(𝐵 - 𝑉) are 0.44 ± 0.05 and 0.34 ± 0.05 mag for SAI 63 and SAI 75 respectively while the corresponding distances are 2.2 ± 0.2 and 3.5 ± 0.3 kpc. An age of 450 ± 50 Myr for SAI 63 and 90 ± 10 Myr for SAI 75 is determined using the theoretical isochrones of Z = 0.019. Our analysis shows that reddening law is normal towards SAI 75.
pp 157-182 June 2014
Prospects for Detecting the 326.5MHz Redshifted 21-cm HI Signal with the Ooty Radio Telescope (ORT)
Sk. Saiyad Ali Somnath Bharadwaj
Observations of the redshifted 21-cm HI fluctuations promise to be an important probe of the post-reionization era (𝑧 ≤ 6). In this paper we calculate the expected signal and foregrounds for the upgraded Ooty Radio Telescope (ORT) which operates at frequency 𝑣_{𝑜} = 326.5MHz which corresponds to redshift 𝑧 = 3.35. Assuming that the visibilities contain only the HI signal and system noise, we show that a 3𝜎 detection of the HI signal (∼ 1 mK) is possible at angular scales 11' to 3° with ≈ 1000 h of observation. Foreground removal is one of the major challenges for a statistical detection of the redshifted 21 cm HI signal. We assess the contribution of different foregrounds and find that the 326.5MHz sky is dominated by the extragalactic point sources at the angular scales of our interest. The expected total foregrounds are 10^{4}−10^{5} times higher than the HI signal.
pp 183-188 June 2014
Chaotic Behaviour of Intra-Day Variability of BL Lac Object S5 0716+714
Shuhong Li Jianwen Ou Zheng Liu
An optical monitoring shows Blazar object S5 0716+714 has complex Intra-Day Variability (IDV) behaviour. In this paper, we introduce a method of non-linear time series analysis, and calculate the correlation dimension of the IDV light curves of S5 0716+714 over seven nights in the December of 2006. According to our calculations, the correlation dimension 𝐷 ≈ 1.993-5.178 for all of the observed data, it is implied that the IDV behaviour may be a chaotic system with some additional noise.
pp 189-200 June 2014
The influence of the gravitational radiation damping on the evolution of the orbital elements of compact binary stars is examined by using the method of perturbation. The perturbation equations with the true anomaly as an independent variable are given. This effect results in both the secular and periodic variation of the semi-major axis, the eccentricity, the mean longitude at the epoch and the mean longitude. However, the longitude of periastron exhibits no secular variation, but only periodic variation. The effect of secular variation of the orbit would lead to collapse of the system of binary stars. The deduced formulae are applied to the calculation of secular variation of the orbital elements for three compact binary stars: PSR 1913+16, PSR J0737-3039 and M33X-7. The results obtained are discussed.
Current Issue
Volume 40 | Issue 5
October 2019
Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.
Click here for Editorial Note on CAP Mode
© 2017-2019 Indian Academy of Sciences, Bengaluru.