• Issue front cover thumbnail

      Volume 30, Issue 2

      June 2009,   pages  79-131

    • Reconnection in Solar Flares: Outstanding Questions

      Hiroaki Isobe Kazunari Shibata

      More Details Abstract Fulltext PDF

      Space observations of solar flares such as those from Yohkoh, SOHO,TRACE, and RHESSI have revealed a lot of observational evidence of magnetic reconnection in solar flares: cusp-shaped arcades, reconnection inflows, plasmoids, etc. Thus it has been established, at least phenomenologically, that magnetic reconnection does occur in solar flares. However, a number of fundamental questions and puzzles still remain in the physics of reconnection in solar flares. In this paper, we discuss the recent progresses and future prospects in the study of magnetic reconnection in solar flares from both theoretical and observational points of view.

    • Spectroscopic Binaries near the North Galactic Pole Paper 12A: 6 Boötis

      R. F. Griffin

      More Details Abstract Fulltext PDF

      About 25 years ago, in Paper 12 of this series, the author presented a spectroscopic orbit for 6 Boo. The velocity amplitude of little more than 1 km s-1 was much smaller than for any star whose orbit had been determined up till that time. Although it was objectively demonstrated that the orbit was very secure, a few years ago subjective misgivings prompted the author to restore the star to his observing programme. Newobservations of much higher precision confirm not only the spectroscopic-binary nature of 6 Boo but also, with almost astonishing fidelity, the elements already given for it.

    • The Ks-band Tully–Fisher Relation – A Determination of the Hubble Parameter from 218 ScI Galaxies and 16 Galaxy Clusters

      David G. Russell

      More Details Abstract Fulltext PDF

      The value of Hubble parameter (H0) is determined using the morphologically type dependent Ks-band Tully–Fisher Relation (K-TFR). The slope and zero point are determined using 36 calibrator galaxies with ScI morphology. Calibration distances are adopted from direct Cepheid distances, and group or companion distances derived with the Surface Brightness Fluctuation Method or Type Ia Supernova. It is found that a small morphological type effect is present in the K-TFR such that ScI galaxies are more luminous at a given rotational velocity than Sa/Sb galaxies and Sbc/Sc galaxies of later luminosity classes. Distances are determined to 16 galaxy clusters and 218 ScI galaxies with minimum distances of 40.0 Mpc. From the 16 galaxy clusters a weighted mean Hubble parameter of H0 = 84.2 ± 6 km s-1 Mpc-1 is found. From the 218 ScI galaxies a Hubble parameter of H0 = 83.4 ± 8 km s-1 Mpc-1 is found. When the zero point of K-TFR is corrected to account for recent results that find a Large Magellanic Cloud distance modulus of 18.39 × 0.05, a Hubble parameter of 88.0 ± 6 km s-1 Mpc-1 is found. Effects from Malmquist bias are shown to be negligible in this sample as galaxies are restricted to a minimum rotational velocity of 150 km s-1. It is also shown that the results of this study are negligibly affected by the adopted slope for the K-TFR, inclination binning, and distance binning. A comparison with the results of the Hubble Key Project (Freedman et al. 2001) is made. Discrepancies between the K-TFR distances and the HKP I-TFR distances are discussed. Implications for 𝛬-CDM cosmology are considered with H0 = 84 km s-1 Mpc-1. It is concluded that it is very difficult to reconcile the value of H0 found in this study with ages of the oldest globular clusters and matter density of the universe derived from galaxy clusters in the context of 𝛬-CDM cosmology.

    • The Effect of Hypothetical Diproton Stability on the Universe

      R. A. W. Bradford

      More Details Abstract Fulltext PDF

      By calculation of the proton–proton capture cross-section, it is shown that the existence of a bound diproton state would not lead to significant production of diprotons during big bang nucleosynthesis, contrary to popular belief. In typical stellar interiors, the stability of diprotons would lead to a reaction pathway for converting protons to deuterons perhaps ∼ 1010 times faster than the usual weak capture reaction. This would prevent stars of the familiar hot, dense type from occurring in the universe. However, if diproton stability is achieved by an increase in the low-energy strong coupling, 𝑔𝑠, then stars with temperatures and densities sufficiently reduced so as to offset the faster reaction pathway to deuterium will appear to meet elementary stability criteria. The claim that there is a fine-tuned, anthropic upper bound to the strong force which ensures diproton instability therefore appears to be unfounded.

  • 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.