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Browsing by Author "Hasan, S. S"

Browsing by Author "Hasan, S. S"

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  • Photospheric Flow Fields and Properties of Embedded Small-scale Magnetic Flux Concentrations 
    Rajaguru, S. P; Srikanth, R; Hasan, S. S (Astronomical Society of the Pacific, 2001)
    The association between the different scales of convection on the solar photosphere and the field strengths/flux contents of discrete magnetic flux elements are analysed using simultaneously recorded SOHO MDI high resolution ...
  • Physics of Photospheric Magnetic Field 
    Van Ballegooijen, A. A; Hasan, S. S (Astronomical Society of the Pacific, 2003)
  • Probing the internal magnetic field of slowly pulsating B-stars through g modes 
    Hasan, S. S; Zahn, J. P; Christensen-Dalsgaard, J (EDP Sciences, 2005-12)
    Context: . Aims: .We suggest that high-order g modes can be used as a probe of the internal magnetic field of SPB (slowly pulsating B) stars. The idea is based on earlier work by the authors hich analytically investigated ...
  • Processes in the magnetized chromosphere of the Sun 
    Hasan, S. S (Cambridge University Press, 2009-03)
    We review physical processes in magnetized chromospheres on the Sun. In the quiet chromosphere, it is useful to distinguish between the magnetic network on the boundaries of supergranules, where strong magnetic fields are ...
  • Radial modes of rotating neutron stars in the Chandrasekhar-Friedman formalism 
    Datta, B; Hasan, S. S; Sahu, P. K; Prasanna, A. R (World Scientific Publishing Company, 1998-02)
    Eigenfrequencies of radial pulsations of "slowly" rotating neutron stars are calculated in a general relativistic formalism given by Chandrasekhar and Friedman (1972). It is found that the square of the frequencies are ...
  • Radiative Transfer Effects and Convective Collapse: Size(flux)-Strength Distribution for the Small-Scale Solar Magnetic Flux Tubes 
    Rajaguru, S. P; Hasan, S. S (Astronomical Society of the Pacific, 1999)
    The effects of radiative energy exchange on the convective instability of a weak field magnetic structure, which lead to a prediction and a physical explanation of the magnetic flux dependent field strength, are examined ...
  • Radiative Transfer Effects and the Dynamics of Small-Scale Magnetic Structures on the Sun 
    Rajaguru, S. P; Hasan, S. S (The American Astronomical Society, 2000-11)
    The dynamical consequences of radiative energy transport on the evolution of gas confined to small-scale magnetic structures on the Sun are studied. Convective collapse, which transforms weak-field structures into intense ...
  • Reconstruction of the past total solar irradiance on short timescales 
    Jain, K; Hasan, S. S (American Geophysical Union, 2004)
    The aim of this investigation is to present a new analysis of short-term variations in total solar irradiance by developing regression models and to extend these to epochs when irradiance measurements were not available. ...
  • Reconstruction of Total Solar Irradiance on Multiple Time Scales 
    Jain, K; Hasan, S. S (Astronomical Society of India, 2003)
    We have developed regression models of total solar irradiance on different time scales by parameterizing the combined influence of sunspots and faculae. These models are useful in identifying the key parameters responsible ...
  • Republication of: radial movement in sunspots 
    Hasan, S. S (Springer, 2010)
    Displacements of the lines of hydrogen and calcium in the neighbourhood of sunspots, indicating violent motions in the line of sight, is a common characteristic of spot disturbances. Such phenomena are frequently observed ...
  • Results from a revisit to the K2V bright points 
    Sivaraman, K. R; Gupta, S. S; Livingston, W. C; Damé, L; Kalkofen, W; Keller, C. U; Smartt, R; Hasan, S. S (European Southern Observatory, 2000-11)
    We have used pairs of temporally simultaneous CaII K-line spectroheliograms and magnetic area scans to search for spatial correlation between the CaII K2V bright points in the interior of the network and corresponding ...
  • Scientific Programmes with India's National Large Solar Telescope and their contribution to Prominence Research 
    Hasan, S. S (Cambridge University Press, 2014-01)
    The primary objective of the 2-m National Large Solar Telescope (NLST) is to study the solar atmosphere with high spatial and spectral resolution. With an innovative optical design, NLST is an on-axis Gregorian telescope ...
  • Solar astronomy at high altitude 
    Hasan, S. S; Bagare, S. P; Rangarajan, K. E (Indian National Science Academy, 2014-11)
    A major project called the National Large Solar Telescope (NLST) has been proposed for pursuing Solar Astronomy at High Altitude. The project envisages the development of a state-of-the-art 2-m class telescope to carry ...
  • Solar physics at the Kodaikanal observatory: a historical perspective 
    Hasan, S. S; Mallik, D. C. V; Bagare, S. P; Rajaguru, S. P (Springer, 2010)
    The Kodaikanal Observatory traces its origins to the East India Company, which started an observatory in Madras “for promoting the knowledge of astronomy, geography, and navigation in India.” Observations began in 1787 at ...
  • Solar physics in India: developments from the nineteenth century to the present era 
    Hasan, S. S; Choudhuri, A. R; Rajaguru, S. P (Astronomical Society of India, 2011)
    Modern solar astronomy took root in India with the discovery of helium during the total solar eclipse of 1868 and followed by the setting up of the Kodaikanal Observatory in 1899. We provide a brief overview of the growth ...
  • Spatial damping of compressional MHD waves in prominences 
    Singh, K. A. P; Dwivedi, B. N; Hasan, S. S (EDP Sciences, 2007-10)
    Aims.We study the spatial damping of linear compressional MHD waves in a homogeneous, isothermal, and unbounded prominence. Methods.We derive a general dispersion relation invoking the Newtonian radiation and turbulent ...
  • Spectral line radiation from solar small-scale flux tubes. II 
    Hasan, S. S; Kneer, F; Kalkofen, W (European Southern Observatory, 1998-04)
    We examine spectral line radiation from small-scale magnetic flux tubes in the solar atmosphere. This is a continuation of work by Kneer et al. (1996). The main difference with the previous investigation is in the choice ...
  • Spectral line radiation from solar small-scale magnetic flux tubes 
    Kneer, F; Hasan, S. S; Kalkofen, W (European Southern Observatory, 1996-01)
    We consider spectral line radiation from small-scale magnetic model flux tubes in the solar atmosphere. The structure of the tube is determined from the magnetostatic equations in the thin flux tube approximation. We assume ...
  • Spectropolarimetry with the NLST 
    Sankarasubramanian, K; Hasan, S. S; Rangarajan, K. E (Springer, 2010)
    India’s National Large Solar Telescope (NLST) will provide opportunities to observe the Sun with high spatial, spectral, and polarimetric resolution. The large aperture also enables high-cadence spectropolarimetry with ...
  • Spectroscopic Observation of Oscillations in the Corona During the Total Solar Eclipse of 22 July 2009 
    Singh, J; Hasan, S. S; Gupta, G. R; Nagaraju, K; Banerjee, D (Springer, 2011-05)
    We performed high resolution spectroscopy of the solar corona during the total solar eclipse of 22 July 2009 in two emission lines: the green line at 5303 Å due to Fe xiv and the red line at 6374 Å due to Fe x, simultaneously ...

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