• Volume 9, Issue 4

      December 1988,   pages  185-248

    • Vortex rings in the working surface of radio jets

      Sandip K. Chakrabarti

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      We study the effects of the presence of vortex rings surrounding a supersonic radio jet inside the cocoon of a radio lobe. We show that both the jet and the shocked ambient medium are pinched. Flow speed inside the cocoon is always close to the sonic value and it stays so by successively passing through several oblique shocks. We also discuss the possibility of the non-linear growth of the instabilities of the contact surface to explain the numerical results in the literature.

    • Composite spectra paper 2: HD 88021/2

      R. Griffin

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      HD 88021/2 (ADS 7662) is a very close visual binary. The accepted visual orbit, which is of very high eccentricity and graded “reliable”, led to the expectation of a periastron passage in 1981, when there should have been a large difference in radial velocity between the components. No such event took place, and there is little indication that it is likely to occur in the near future. A new interpretation of the visual orbital data leads to an orbit of a different character from those hitherto proposed. A decision between the competing orbits should be possible within a very few years. Meanwhile, the method of spectral subtraction developed in Paper 1 has enabled us to separate the spectra of the two components and to show that their spectral types are K0 III and A2m.

    • Spectroscopic binaries near the North Galactic Pole paper 16: HD 116093

      R. F. Griffin

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      Photoelectric radial-velocity measurements show that HD 116093 is a double-lined spectroscopic binary in a very eccentric 53-day orbit. Very little else is known about the system, but circumstantial evidence is consistent with the hypothesis that the components’ types are near to F3 V and F8 V. If that is so, the orbit must be seen very nearly edge-on; a search for eclipses is warranted and an ephemeris for them is given.

    • HD 115781 and HD 116204—two RS CVn binaries

      R. F. Griffin Francis C. Fekel

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      HD 115781 and HD 116204 (BL CVn and BM CVn) are shown to be RS CVn binaries with periods near 20 days. HD 115781 is double-lined; the primary type is about K1III, while the secondary is probably a late-type subgiant. The masses of the two components are equal within observational error. There is substantial photometric variability with a period half the orbital period; it is attributed to ellipsoidal variation. HD 116204 is also of type K1III. It shows exceptionally strong Ca II H and K emission, together with an emission-line spectrum typical of RS CVn stars in theIUE ultraviolet region, but Hα is an absorption line. The secondary star in the HD 116204 system has not been detected. The primary shows photometric variations, presumably due to starspots, with a period 5 per cent longer than the orbital period.

    • The low-frequency radio spectrum of the continuum emission from the undisturbed sun

      K. R. Subramanian Ch. V. Sastry

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      The low-frequency radio spectrum of the continuum emission from the undisturbed Sun is determined for 24 days during the period 1985 May-September. It is found that the spectral index varied from + 1.6 to +3.6 during this period. It is suggested that the large positive spectral indices are due to the existence of temperature gradients in the outer corona.

    • One more explanation of superluminal motion

      V. Krishan

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      The occurrence of superluminal motion in extragalactic radio sources is believed to be quite common. Among others, the geometrical scattering of radio radiation can also cause superluminal expansion and or motion and halo formation, In this paper, the effectiveness of the stimulated Raman scattering in producing these features is investigated. The scattering medium is a plasma whose position, density and temperature decide the rate and angle of scattering. When the radiation from a stationary and constant source gets scattered from a stationary plasma, a halo is formed around the source. However, the scattering of a rotating radiation beam does produce superluminal motion of the virtual source. It is found that the plasma should have the characteristics of the emission-line regions and the intercloud medium in order to Raman scatter the radiation. Since the scattering is polarization dependent, it is possible to estimate the rotation of the electric vector along the direction of the apparent motion of a radio source.

    • The O III 52 ▪m/88 ▪m emission-line ratio in planetary nebulae

      F. P. Keenan K. M. Aggarwal

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      R-matrix calculations of electron impact excitation rates in 0 III are used to derive the electron-density-sensitive emission-line ratioR = 1 (2s2 2p23P2-2s22P23P1)/I (2s22p23P1 - 2s22p23P0) =I (52μm)/I (88μm) for a range of electron temperatures(Te = 5000-20000 K) and densities(Ne=10–105 cm−3) applicable to planetary nebulae. Electron densities deduced from the observed values ofR in several planetary nebulae are in excellent agreement with those deduced from C1 I and Ar IV, which provides support for the accuracy of the atomic data adopted in the calculations.

    • On the damping of the bending waves in Saturn’s ring

      Sandip K. Chakrabarti

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      We study numerically the motion of a single particle in the bending wave of finite thickness in Saturn’s ring. We include the forcing due to the planet, a moon, the coriolis force and the self gravity of the ring. In particular, we compute the variation of the velocity arising due to the variation of the amplitude and the phase of the epicyclic motion across the local vertical height of the ring. We suggest that the dissipation of energy due to the collision of ring particles in this shear layer damps out the bending wave of Saturn’s ring at the 5:3 vertical resonance of Mimas within a distance of 150 km from the site of its launching as is observed in Voyager data.

  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      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.

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