• Volume 12, Issue 2

      June 1991,   pages  91-178

    • Ejections of quasars at relativistic speeds from nearby galaxies: Ejection mechanism and selection effects

      M. J. Valtonen D. Basu

      More Details Abstract Fulltext PDF

      It has become part of the conventional wisdom of quasar research that quasars cannot be objects ejected from nearby galaxies. The reasons are summarized in Burbidge & Burbidge (1967) and they include: (1) in quasar spectra only redshifts, and no blueshifts, are observed, contrary to expectation in a local Doppler interpretation of quasar line shifts; (2) the energy requirements for relativistically moving quasars seem excessive and the ejection mechanism is unknown. In. this work we show that the first problem could be explained via some powerful selection effects, and that the second problem does not exist in the relativistic slingshot process of ejecting black holes. Consequently one cannot exclude the possibility that at least some of the quasar-galaxy associations of large redshift differentials discussed by Arp and Sulentic are real and that the redshift differences are due to high speeds of ejected quasars

    • Emission-line CCD imaging of three southern symbiotic stars

      Harish C. Bhatt Ram Sagar

      More Details Abstract Fulltext PDF

      Symbiotic stars that are strong radio sources and have cool dust emitting in the infrared are expected to have extended emission nebulae around them. In order to search for such emission nebulae, we have carried out CCD imaging of three symbiotic stars (R Aqr, RR Tel and H1-36) with narrow-band filters centred at the emission lines of [O III] λ5007, Hα λ6563, [N II] λ6584, [S II] λ6717 + 6731. RR Tel and H1-36 images do not show any extended nebulosities around them. The CCD image of the R Aqr nebulosity in the high excitation [O m] line is different from its image in Hα and the low excitation lines of [N II] and [S II] indicating ionization-stratification in the nebula. In H1-36 the optical nebulosity (if it exists) is smaller than ∽2 arcsec while the radio image size is known to be large (∽5 arcsec). This behaviour is opposite to that seen in R Aqr in which the radio emission comes from the core region of a much larger optical nebulosity. Interstellar and/or circumstellar extinctions are suggested to be responsible for this difference

    • BV 690, a new bright Type II Cepheid

      N. B. Sanwal M. B. K. Sarma

      More Details Abstract Fulltext PDF

      B andV observations of the suspected variable BV 690 = NSV 04298 are reported. The star shows light variations with a period of ld.2400 and with amplitudes of 0m.27, 0m.36 and 0m.11 inV, B, andB-V respectively. The light curves show steeper rise than decline, and there is evidence for the presence of a bump in the descending branch around the phase of 0.35. From considerations of the period, spectral type, presence of the bump and high tangential velocity we conclude that BV 690 belongs to the BL Herculis class of Typen Cepheids

    • MK morphological study of Am stars at 66 Å/mm

      S. Sreedhar Rao K. D. Abhyankar

      More Details Abstract Fulltext PDF

      The pseudo-luminosity effect in the metallic line A-type stars found by Abt & Morgan (1976) is confirmed in a random sample of 27 Am stars. From a morphological study of their spectra in the wavelength interval 3850-4400 Å at a reciprocal dispersion of 66 Å/mm, revised spectral types are given on the MK system for their K-line and metallic-line spectra. This shows that: (a) our segregation of weak Am from the Am stars largely agrees with that by Cowleyet al. (1969); (b) all the stars in the sample are dwarfs according to their K-line classification; (c) more than 80 per cent exhibit the pseudo-luminosity effect significantly, with their metallic-line spectra resembling a giant or even a supergiant in the violet (3850-4100 Å), and a giant rather than a dwarf in the blue region (4260-4400 Å); (d) in two-thirds of the stars under (c), the Sr n 4077 Å line is found to have a markedly brighter luminosity class compared to any region, and in more than one-third of the sample it is comparable to that in Ap stars; (e) at least five stars exhibit characteristics which might suggest a spectrum variability: among these, the most striking example is 41 Sex A which was found to show a phase-modulated spectrum variation hitherto unknown in Am stars; (f) the metallic-line spectra of another five stars appear to be similar to A-shell type in differing degrees; (g) less than 20 per cent of the sample comprises stars which do not show any significant differential luminosity effect; these stars might have been misclassified or perhaps they are in a quiescent state.

      We also confirm the conclusion arrived at by Böhm-Vitense & Johnson (1978) that all Am stars may vary and our observations suggest that groups may exist among them.

  • 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.

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

© 2017-2019 Indian Academy of Sciences, Bengaluru.