IUCAA Preprints

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    Site characterization for the IUCAA telescope
    (2015-03-11) Das, H.K.; Menon, S.M.; Paranjpye, A.; Tandon, S.N.
    We present the report on characterisation of the site for IUCAA telescope, which was conducted during October '96 to April '97. The main points highlighted are the results on: seeing, contribution of atmospheric turbulence neai• the surface to seeing , extinction and sky brightness, cloud coverage and surface weather data. In addition the key design features of the instruments developed for these observations are presented.
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    Systematic Variations of Interstellar linear polarization and growth of dust graint
    (IUCAA, 2015-02) Voshchinnikov, N.V.; Das, H.K.; Yakovlev, I. S.
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    Implementation of transfer-pupil in a spectrograph on optical telescopes
    (2011-07-06) Das, H.K.; Kohok, Abhay; Tandon, S. N.
    Based on the transfer pupil technique we develop a method to measure the lower order aberration coe±cients for optical telescopes; the method makes use of a Hartmann mask in a spectrograph for sampling the wavefront at di®erent locations.
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    Modelling interstellar extinction and polarization with spheroidal grains
    (2008-01) Voshchinnikov, N. V.; Das, H.K.
    We calculate the wavelength dependence of the ratio of the linear polarization degree to extinction (polarizing efficiency) P(λ)/A(λ) from the ultraviolet to ear-infrared. The prolate and oblate particles with aspect ratios from a/b = 1.1 up to 10 are assumed to be rotating and partially aligned with the mechanism of paramagnetic relaxation (Davis-Greenstein). Size/shape/orientation effects are analyzed. It is found that the wavelength dependence of P(λ)/A(λ) is mainly determined by the particle composition and size whereas the values of P(λ)/A(λ) depend on the particle shape, degree and direction of alignment.
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    Interstellar extinction and polarization - A spheroidal dust grain approach perspective
    (2010-01-10) Das, H.K.; Voshchinnikov, N. V.; Il'in, V.B.
    We extend and investigate the spheroidal model of interstellar dust grains used to simultaneously interpret the observed interstellar extinction and polarization curves. We compare our model with similar models recently suggested by other authors, study its properties and apply it to fit the normalized extinction A(λ)/AV and the polarizing efficiency P(λ)/A(λ) measured in the near IR to far UV region for several stars seen through one large cloud. We conclude that the model parameter Ω being the angle between the line of sight and the magnetic field direction can be more or less reliably determined from comparison of the theory and observations. This opens a way to study the spatial structure of interstellar magnetic fields by using multi-wavelength photometric and polarimetric observations.