Astrophysics and Space Science

In this paper we present a method for computing the equilibrium structures and various physical parameters of a primary component of the binary system assuming that the primary is more massive than the secondary and is rotating differentially according to the law of the w2 = b0 + b1 × s2 + b2 × s4, w being the angular velocity of rotation of a fluid element distant s from the axis of rotation and b0, b1, b2 suitably chosen numerical constants. This method utilizes the averaging approach of Kippenhahn and Thomas (1997) and the concept of Roche equipotentials in a manner earlier used by Mohan et al. (1997) to incorporate the effects of rotation and tidal distortions on the equilibrium structures of certain rotationally and tidally distorted stellar models. The use of the method has been illustrated by applying it to obtain the structures and some observable parameters of certain differentially rotating and tidally distorted binary systems whose primary component is assumed to be a white dwarf star.

Transverse oscillatory motions and recurrence behavior in the chromospheric jets observed by Hinode/SOT are studied. A comparison is considered with the behavior that was noticed in coronal X-ray jets observed by Hinode/XRT. A jet like bundle observed at the limb in Ca II H line appears to show a magnetic topology that is similar to X-ray jets (i.e., the Eiffel tower shape). The appearance of such magnetic topology is usually assumed to be caused by magnetic reconnection near a null point. Transverse motions of the jet axis are recorded but no clear evidence of twist is appearing from the highly processed movie. The aim is to investigate the dynamical behavior of an incompressible magnetic X-point occurring during the magnetic reconnection in the jet formation region. The viscous effect is specially considered in the closed line-tied magnetic X-shape nulls. We perform the MHD numerical simulation in 2-D by solving the visco-resistive MHD equations with the tracing of velocity and magnetic field. A qualitative agreement with Hinode observations is found for the oscillatory and non-oscillatory behaviors of the observed solar jets in both the chromosphere and the corona. Our results suggest that the viscous effect contributes to the excitation of the magnetic reconnection by generating oscillations that we observed at least inside this Ca II H line cool solar jet bundle.

A network of families of periodic orbits is obtained approximately for the case μ=0.1 of the restricted problem using a direct grid search. Only such orbits of the third body are considered that cross the synodical line of the primaries ‘outside’ the smaller of the two, perpendicularly, and in the direction of rotation of the system.

Các mô hình máy tính về các trường thiên hà được tạo ra bằng cách sử dụng kỹ thuật mô phỏng Monte-Carlo được mô tả trong Bài báo I (MacGillivray et al., 1982b). Trong các mô hình, nhiều kịch bản về phân bố 3 chiều thật sự của các thiên hà (ví dụ: sự cụm lại trên các thang đo liên tục hoặc phân cấp) được bao gồm và các thiên hà được chiếu lên một tấm phim tổng hợp. Tất cả các yếu tố ảnh hưởng đến ánh sáng từ các thiên hà xa xôi đều được xem xét trong các mô phỏng, cũng như các yếu tố ảnh hưởng đến việc phát hiện và đo lường hình ảnh của những thiên hà mờ trên các tấm phim được quét bằng một máy đo tấm phim tự động. Các trường mô hình được so sánh, cả về mặt chất lượng và thống kê, với một trường thu được từ các phép đo với COSMOS trên một bức ảnh sâu được chụp bằng kính thiên văn Schmidt của Vương quốc Anh. Kết quả cho thấy rằng phân bố quan sát được của các thiên hà mờ trên các tấm phim chỉ có thể được đại diện bằng một mô hình liên quan đến sự cụm lại bậc hai của các thiên hà. Tuy nhiên, tính chất chính xác của sự cụm lại bậc hai này không thể được xác định một cách rõ ràng từ các phân bố 2 chiều, cả mô hình siêu cụm đồng nhất và mô hình tế bào đều có thể đại diện thống kê cho phân bố chiếu dự kiến của các thiên hà.

The classical situation of dynamical systems with two degrees of freedom is completely modified by the introduction of a stochastic element which provides a slow dissolution of the zone of stability. Using a Fokker-Planck method it has been shown that the Gambler's ruin problem is a rather good approximation of the diffusion process. Furthermore the orbits exhibit aC-system character even during the diffusion process.

An exact solution pertaining to the existence of cosmic strings has been discussed for a cylindrically symmetric $f(\mathcal{G},T)$ gravity model, with $\mathcal{G}$ being the Gauss-Bonnet invariant and $T$ the trace of energy momentum tensor. This solution corresponds to the generalised vacuum Levi-Civita’s metric in general relativity. Exclusive expressions for the energy density and pressure terms along with their corresponding null energy constraints have been worked out and analyzed graphically. It has been shown that the energy density remains positive and the null energy conditions are met largely for some particular choices of the parametric terms appearing in the model. However, certain violation of these energy constraints under specific circumstances hints the existence of cylindrical wormholes. Moreover, if the coupling constant of the Gauss-Bonnet invariant is set to null, Levi-Civita vacuum solution in general relativity is recovered.

We discuss the distribution of dust and atomic hydrogen in and around a small dark cloud nearρ Ophiuchi. Although the obscuration reaches values as high as 8 magnitudes, the values ofN H derived inside the cloud do not differ markedly from those found at nearby, less obscured points. At low values of the obscuration, dust and hydrogen isophotes show satisfactory agreement, i.e.,N H increases withN G. However, we find thatN H starts decreasing for sufficiently large values ofN G. In the entire range of optical extinctions investigated our observations are satisfied by an expression of the typeN H=AN G exp (-BN G). Interpretation of this relationship suggests that an appreciable part of the hydrogen has been converted to molecular form inside the cloud. A tentative method for calculating the time elapsed since the conversion process began is proposed.

Amongst the sources seen in very high gamma-rays several are associated with Pulsar Wind Nebulae (“TeV plerions”). The study of hard X-ray/soft gamma-ray emission is providing an important insight into the energetic particle population present in these objects. The unpulsed emission from pulsar/pulsar wind nebula systems in the energy range accessible to the INTEGRAL satellite is mainly synchrotron emission from energetic and fast cooling electrons close to their acceleration site. Our analyses of public INTEGRAL data of known TeV plerions detected by ground based Cherenkov telescopes indicate a deeper link between these TeV plerions and INTEGRAL detected pulsar wind nebulae. The newly discovered TeV plerion in the northern wing of the Kookaburra region (G313.3+0.6 powered by the middle aged PSR J1420-6048) is found to have a previously unknown INTEGRAL counterpart which is besides the Vela pulsar the only middle aged pulsar detected with INTEGRAL. We do not find an INTEGRAL counterpart of the TeV plerion associated with the X-ray PWN “Rabbit” G313.3+0.1 which is possibly powered by a young pulsar.

In this panel discussion contributions were made by K. Strom, L. Nordh and H. Zinnecker on the contributions of surveys to the study of star formation regions, by B. Burton on a survey of galactic H I and by E. Dwek on the detection of galactic supernovae by infrared surveys. The contributions of K. Strom, L. Nordh and E. Dwek are summarized here.