IGO Publications

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Author: search.filters.author.Das, H.K.Start date: 2010

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    Design and development of an optical-fibre-based Integral Field Unit (IFU) on the IUCAA 2-m telescope
    (Mon. Not. R. Astron. Soc., 2011-07-31) Srivastava, Mudit K.; Ramaprakash, A.N.; Das, H.K.
    An optical-fibre-based Integral Field Unit (IFU) has been developed for the Inter-University Centre for Astronomy and Astrophysics (IUCAA) Faint Object Spectrometer and Camera (IFOSC), the main back-end instrument on the IUCAA 2-m telescope at Girawali, Pune, India. This IFU enables IFOSC to perform two-dimensional spectroscopy of extended astronomical objects and is being used as one of the modes of IFOSC. Based on the concept of coupling the telescope focal plane with the spectrograph slit using a fibre bundle, the IFU (named the Fibre-based Integral Field Unit for IFOSC, hereafter FIFUI) uses 100 optical fibres, each associated with a tiny lenslet on its tip, to sample the incoming field of view spatially. In addition, FIFUI uses some coupling optics to realize this two-dimensional interface. FIFUI offers three different spatial sampling scales of 0.8, 1.0 and 1.2 arcsec fibre−1. It is optimized for the visible spectrum and for a field of view of ∼13 × 6 arcsec2 on the sky for the nominal 1-arcsec sampling mode. FIFUI was commissioned on the IUCAA 2-m telescope during 2010 February–March after a series of sky tests and science-verification observations and a dataanalysis pipeline was developed to extract the spectra and reconstruct the sky maps. Here we report on the development of FIFUI, including its opto-mechanical design and commissioning observations.
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    Interstellar extinction and polarization – a spheroidal dust grain approach perspective
    (2010-01-15) 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-infrared to far-ultraviolet region for several stars seen through one large cloud. We conclude that the model parameter 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 multiwavelength photometric and polarimetric observations.