Browsing by Author "Sahu, D. K."

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    Photometric and Spectroscopic study of a highly reddened type Ia supernova SN 2003hx in NGC 2076
    (2008-01-28) Misra, Kuntal; Sahu, D. K.
    We present UBV RI CCD photometry and optical spectra of the type Ia supernova SN 2003hx which appeared in the galaxy NGC 2076, obtained till ∼ 146 days after the epoch of B band maximum. The supernova reached at maximum brightness in B band on JD 245 2893 ± 1.0 with an apparent magnitude of 14.92 ± 0.01 mag which was estimated by making template fits to the light curves. SN 2003hx is an example of a highly reddened supernova with E(B −V ) = 0.56 ± 0.23. We estimate Rv = 1.97 ± 0.54 which indicates the small size of dust particles as compared to their galactic counterparts. The luminosity decline rate is ∆m15(B) = 1.17 ± 0.12 mag and the absolute B band magnitude obtained from the luminosity versus decline rate relation (Phillips et al. 1999) is MB max = -19.20 ± 0.18 mag. The peak bolometric luminosity indicates that ∼ 0.66 M⊙ mass of 56 Ni was ejected by the supernova. The spectral evolution indicates the supernova to be a normal type Ia event.
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    Properties of dust in early-type galaxies
    (2006-11-12) Patil, M. K.; Pandey, S. K.; Sahu, D. K.; et al.
    We report optical extinction properties of dust for a sample of 26 early-type galaxies based on the analysis of their multicolour CCD observations. The wavelength dependence of dust extinction for these galaxies is determined and the extinction curves are found to run parallel to the Galactic extinction curve, which implies that the properties of dust in the extragalactic environment are quite similar to those of the Milky Way. For the sample galaxies, value of the parameter RV, the ratio of total extinction in V band to selective extinction in B & V bands, lies in the range 2.03 - 3.46 with an average of 3.02, compared to its canonical value of 3.1 for the Milky Way. A dependence of RV on dust morphology of the host galaxy is also noticed in the sense that galaxies with a well defined dust lane show tendency to have smaller RV values compared to the galaxies with disturbed dust morphology. The dust content of these galaxies estimated using total optical extinction is found to lie in the range 104 to 106 M⊙, an order of magnitude smaller than those derived from IRAS flux densities, indicating that a significant fraction of dust intermixed with stars remains undetected by the optical method. We examine the relationship between dust mass derived from IRAS flux and the X-ray luminosity of the host galaxies.The issue of the origin of dust in early-type galaxies is also discussed.