Professor Ranjan Gupta

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    Interstellar extinction by composite grains
    (Astronomy & Astrophysics, 2001-06-24) Vaidya, D.B.; Gupta, R; Dobbie, J.S.; et.al
    Recent studies indicate that interstellar grains are composites of very small individual particles of silicates and carbon glued together into an aggregate. Using the discrete dipole approximation (DDA), we calculate the extinction, scattering and absorption e ciencies for composite grains assumed to be made of a host silicate sphere with embedded graphite inclusions. In particular, we study the extinction as a function of inclusion size and volume fraction. Using the extinction e ciencies of these composite grains, we evaluate the interstellar extinction curve in the wavelength region of 0:55 m−0:20 m.
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    Imaging polarimetry of some selected dark clouds?
    (Astron. Astrophys. Suppl. Ser., 2000-01-11) Sen, A.K.; Gupta, Ranjan; Ramaprakash, A.N; et al.
    A set of eight Bok Globules CB3, CB25, CB39, CB52, CB54, CB58, CB62 and CB246 were observed polarimetrically in white light, using our Imaging Polarimeter (IMPOL), from the 1.2 m IR telescope at Mount Abu, India. The observations were carried out on di erent nights during the period December 1997 and April 1998. The CCD images obtained from the instrument (IMPOL) were analyzed, to produce polarization map of the Bok Globules. The stars in the eld, which are mostly background to the cloud show typically 2% of linear polarization. Clouds which are less dynamic (having 12CO line widths V < 2:5 km s−1), in general show slightly better alignment of polarization vectors with the projected direction of galactic plane. On the other hand the more dynamic group of clouds, has the polarization vectors more scattered and poorly aligned with the projected direction of the galactic plane. However one of the clouds observed CB58 does not follow this trend very well.
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    Interstellar extinction by porous grains
    (Astron. Astrophys., 1999-04-23) Vaidya, D.B.; Gupta, Ranjan