T. P. Prabhu
Articles written in Journal of Astrophysics and Astronomy
Volume 1 Issue 2 December 1980 pp 129-154
A classification scheme is proposed for the central regions of Sérsic-Pastoriza galaxies based on high resolution photographs of 50 objects in the integrated light (4000 Å-8700 Å). Structures of two different linear scales are recognized: (1) nucleus(≲1 kpc) and (2) perinuclear formation (∼l.5 kpc). The perinuclear formation is weak in class
The peak central surface brightness of the perinuclear formation varies as the square of the bar length. This relation implies that the bar induces the infall of gas from the bar-disk region.
The formations of class
The central brightness of the bars varies directly as the length of the bar.
Volume 8 Issue 2 June 1987 pp 195-209
The evolution of the spectrum of SN1987a is traced from 1987 February 26 to March 31. Based on the low-resolution spectroscopic data we identify the lines of H, He I, Na I, Fe II, Sc II, Ca II which are known to be present in Type II Supernovae, and also present evidence for the existence of lines of Mg I, CaI, O I, and N I. We discuss the evolution of the Hα profile, and draw attention to its complex structure around March 30. Close to the rest wavelength of Ha a double-peaked structure appeared in the profile with a peak-to-peak separation of ∼ 1400 km s−1, suggestive of an expanding shell or disc of gas.
Using the available broadband photometric information, we also trace the evolution of the photosphere of SN1987a assuming that it radiates like a supergiant.
Volume 8 Issue 4 December 1987 pp 369-387
Optical spectroscopic data are presented on nova LW Serpentis 1978, obtained during its decline from
Volume 10 Issue 3 September 1989 pp 237-255
Optical spectroscopic data on the recurrent nova RS Ophiuchi obtained between 32 and 108 days after its last outburst on 1985 January 27 are presented. RS Oph was in the coronal-line phase at that time. The widths of the permitted as well as coronal-lines decreased continuously. Assuming that the ejected envelope decelerated due to its interaction with circum stellar matter, its size is deduced as a function of time. Observed fluxes in permitted lines would then imply that the electron density decreased from 3 × 109 cm#x2212;3 on day 32 to 1.8 × 108 cm-3 on day 108, for an assumed filling factor of 0.01. The helium abundance in the ejecta is estimated to be n(He)/n(H) ∼ 0.16. The mass of the unshocked ejecta was 3 × 10-6 (Φ/0.01)1/2 M⊙, (at this stage, where f is the filling factor. Observed fluxes in coronal-lines imply that the temperature of coronal-line region decreased from 1.5 × 106 K on day 32 to 1.1 × 106 K on day 108. Most of the coronal line emission, as well as He n emission arises in shocked and cooling ejecta. This region is not isothermal, but contains material at a wide range of temperatures. Mass of the shocked ejecta is estimated to be in the range 10−7−10−6 M⊙ Based on the number of H- and He-ionizing photons, we estimate that the ionizing source evolved from a radius and temperature of (2 × l012 cm, 3 × 104 K) on day 32 to (6 × l09 cm, 3.6 × 105K) on day 204.
We also present the spectra of RS Oph recorded in quiescent phase, 2 and 3 years after outburst, for comparison. The spectrum is dominated by that of M2 giant secondary, with superposed emission lines of H and He I
Volume 13 Issue 1 March 1992 pp 129-144
The system gain of two CCD systems in regular use at the Vainu Bappu Observatory, Kavalur, is determined at a few gain settings. The procedure used for the determination of system gain and base-level noise is described in detail. The Photometrics CCD system at the 1-m reflector uses a Thomson-CSF TH 7882 CDA chip coated for increased ultraviolet sensitivity. The gain is programme-selected through the parameter ‘cgain’ varying between 0 and 4095 in steps of 1. The inverse system gain for this system varies almost linearly from 27.7 electrons DN-1 at cgain = 0 to 1.5 electrons DN-1 at cgain = 500. The readout noise is ≲ 11 electrons at cgain = 66. The Astromed CCD system at 2.3-m Vainu Bappu Telescope uses a GEC P8603 chip which is also coated for enhanced ultraviolet sensitivity. The amplifier gain is selected in discrete steps using switches in the controller. The inverse system gain is 4.15 electrons DN-1 at the gain setting of 9.2, and the readout noise ∼ 8 electrons.
Volume 13 Issue 4 December 1992 pp 293-305
We present the results from CCD photometry in the
Volume 40 | Issue 5
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