• M. K. V. Bappu

      Articles written in Journal of Astrophysics and Astronomy

    • Preface

      M. K. V. Bappu

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    • Mass segregation in globular clusters

      K. K. Scaria M. K. V. Bappu

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      Photoelectric aperture-photometry ofω Cen inU, B, V, R andI bands has established that the cluster is bluer between 2 arcmin and 4 arcmin from the centre, than it is elsewhere. The difference inB - I colour between the centre and this blue zone is ≃ 0.45 mag. The core radius is found to be dependant on the wavelength band chosen for observation, the smallest core radius being for theI band. Equidensitometry ofω Cen inB, V and infrared bands shows a wavelength dependence with the cluster being nearly spherical in the infrared band. It shows a maximum ellipticity around 3 arcmin from the cluster centre. The blue contribution in this zone comes from both a diffuse background of unresolved stars and an increase in the relative abundance of horizontal branch (HB) stars. The similarity between the diffuse background and the HB stars has been demonstrated. A photographic subtraction technique is used to study the distribution of HB stars in the cluster.

      Results of equidensitometry of the cluster 47 Tuc, obtained in the present study, are compared with the earlier results of photoelectric photometry. Here too an increase in ellipticity is associated with an increase in the blueness of the cluster. All globular clusters studied so far for ellipticity show a similarity in the dependence of the ellipticity on the distance from the centre. The ellipticity has small values near the centre and in the outer regions, with the maximum value in between. We suggest that the red stars in globular clusters have a nearly spherical distribution. The blue stars form a bulge around the core with a more elliptical distribution and a different orientation. A similarity between the ellipticity aspects of both the globular clusters and rotation in the nucleus of M 31 is pointed out; the M 31 nucleus may thus show a bluer colour and smaller UV excess around the region where the rotation curve shows a peak.

    • Corrigendum

      K. K. Scaria M. K. V. Bappu

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    • Eclipse observations of coronal emission lines. I. [Fex] 6374Å profiles at the eclipse of 16 February 1980

      Jagdev Singh M. K. V. Bappu A. K. Saxena

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      Coronal spectra during the total solar eclipse of 1980 February 16, were obtained in the 6374Å [Fex] line using a multislit spectrograph. These spectra have a dispersion of 2.5 Å mm-1. The observed line profiles from 1.1 to 1.7 R with a spatial resolution of 10 × 22 arcsec2, give half-widths that vary between 0.6 Å and 2.4Å. A large number of locations have half-widths around 1.3 Å corresponding to a temperature of 4.6 × 106 K. If temperature of the order of 1.3 × 106 K are typical of the regions that emit [Fex], then turbulent velocities of ~ 30 km s-1 need to be invoked for the enhanced line broadening. The line-of-sight velocities measured range between +14 km s-1 to -17 km s-1. Most of the locations have velocities less than ±5 km s-1. From these observations we conclude that corona does not show any localized differential mass motion and that it co-rotates with the photospheric layers deeper down.

    • Chromospheric activity of late-type giants and supergiants: Reappearance of dynamo activity in the interior due to the spin-up of the core in evolution

      Yutaka Uchida M. K. V. Bappu

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      The renewal of chromospheric activity in red giants and supergiants is interpreted in terms of the reappearance of dynamo activity in the interior due to the spin-up of the core caused by its contraction in the course of evolution from the main sequence to the giant stage. A region of very high rotational shear (differential rotation) develops between the core, which spins up by a large factor through the drastic contraction, and the envelope, which spins down in contrast by virtue of expansion. Mechanisms of angular momentum transfer may operate to smear this large shear, and bring the inner part of the envelope into sheared rotation. A convective layer, on the other hand, develops in the envelope from the surface inwards, when the envelope expands and the temperature is lowered. A dynamo layer, or a layer in which the sheared rotation co-exists with the convection (the presence of a remnant magnetic field being postulated), will thus reappear in the inner part of the envelope when the envelope-convection reaches down and invades the layer of sheared rotation. Surface chromospheric activity due to the magnetic field is thus renewed when the regenerated magnetic field is brought up to the surface by the envelope-convection. These phenomena occur as the star evolves into the giant stage and hence explain the observed characteristic of gradual revival of chromospheric activity from the subgiant to the giant stage.

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      Posted on January 27, 2016

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