A5045484078- Astro and Planetary Science
- Stellar, planetary, and galactic studies
- Planetary Science and Exploration
- Astrophysics and Star Formation Studies
- Pulsars and Gravitational Waves Research
- Nuclear Physics and Applications
- Cosmology and Gravitation Theories
- Relativity and Gravitational Theory
- Isotope Analysis in Ecology
- Astronomy and Astrophysical Research
- Solar and Space Plasma Dynamics
- Geophysics and Gravity Measurements
- Astrophysical Phenomena and Observations
- Atmospheric aerosols and clouds
- Atmospheric Ozone and Climate
- Geophysics and Sensor Technology
- Calibration and Measurement Techniques
- Experimental and Theoretical Physics Studies
- Optical Polarization and Ellipsometry
- Adaptive optics and wavefront sensing
- Astronomical Observations and Instrumentation
- Black Holes and Theoretical Physics
- Mass Spectrometry Techniques and Applications
- Galaxies: Formation, Evolution, Phenomena
- Gamma-ray bursts and supernovae
Assam University
2014-2024
Inter-University Centre for Astronomy and Astrophysics
1994-2014
Centre of Plasma Physics - Institute for Plasma Research
1997
Physical Research Laboratory
1987-1992
Geological Survey of India
1974
We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on the Subaru Telescope. has been classified as a pre-transitional disk object, gap structure separating its inner and outer disks. Our 0.15 (21 AU) radius coronagraphic mask revealed strongly polarized circumstellar surrounding which extends to 120 AU, at spatial resolution 0.1 (14 AU). It is inclined by 46 \pm 2 degree west side nearest. Although SED modeling sub-millimeter suggested presence in disk, edge estimated...
Recently, the result obtained from `Stardust' mission suggests that overall ratio of compact to aggregate particles is 65:35 (or 13:7) for Comet 81P/Wild 2 (Burchell et al. 2008). In present work, we propose a model which considers cometary dust as mixture and particles, with composition silicate organic. We consider spheroidal aggregates BCCA BAM2 some size distribution. For modeling 1P/ Halley, power-law distribution n(a)= a^{-2.6}, both taken. take lower upper cutoff around 0.20$\mu m$...
Remote observations of the light scattered by dust particles in comet 67P/Churyumov–Gerasimenko (67P/C-G) (photometry and imaging polarimetry) allow us to compare deduced physical properties these with situ measurements provided Rosetta mission. Onboard experiments on confirm inferred from polarimetric laboratory experiments, namely existence large dark size range 10–500 μm, which could be fluffy compact aggregates smaller grains (submicron- micron-sized) possibly particles. The 2008–2009...
Taking advantage of the advances in array detector technology, an imaging polarimeter (IMPOL) has been constructed for measuring linear polarization wavelength band from 400-800 nm. It makes use a Wollaston prism as analyzer to measure simultaneously two orthogonal components that define Stoke's parameter. An achromatic half-wave plate is used rotate plane with respect axis so second parameter also can be determined. With field view corresponding about 20/D 1.2 m, f/13 telescope, sensitive,...
An analytical model has been developed to estimate the polarization effects, such as instrumental (IP), crosstalk (CT), and depolarization, due optics of Thirty Meter Telescope. These are estimated for unvignetted field-of-view wavelengths interest. The estimates an IP 1.26% a CT 44% at Nasmyth focus telescope wavelength 0.6 μm field angle zero with pointing zenith. Mueller matrices have primary, secondary, mirrors. It is found that some matrix elements primary secondary mirrors show...
In the present work, light-scattering properties of comet Levy 1990XX are studied through simulations using Ballistic Particle-Cluster Aggregation (BPCA) or Cluster–Cluster (BCCA) aggregates up to 128 spherical monomers different compositions (e.g. silicates, carbonaceous materials etc.) and best-fitting theoretical polarization curve is generated Superposition T-matrix code. The refractive indices coming out from analysis show silicate behaviour when monomer radius am= 0.12 μm provide...
Abstract Comet C/2009 P1 (Garradd) was observed by imaging polarimetry for nearly 5 months from October 2011 to March 2012, over an intermediate phase angle range (28°–35°). Two before perihelion and one month after, dust particles seem be ejected all around the optocenter jets extend distances greater than 40,000 km. An increase of activity is noticed in intensity polarization after perihelion. emission seems optocenter. three are mainly toward solar direction with extension more 20,000 km...
Under the frame work of Mie theory, a method has been developed to calculate absorbance spectra nanoparticles suspension containing size distribution. The silver two different sizes were first synthesized using chemical reduction and characterized by UV-Visible spectroscopy, dynamic light scattering, transmission electron microscopy techniques. A model size-distribution proposed fitted experimental described method. Better semiqualitative fitting obtained our in comparison those single...
According to GTR and subsequent developments in the field, it is known that there are three factors namely mass, rotation charge can influence space-time geometry. Accordingly, we discuss effect of geometry a charged, rotating body on motion light ray. We obtained expression for equatorial defection due such up fourth order term. In our angle clear path used null geodesic approach ray calculation. If set zero bending gets reduced Kerr angle.If reduces Resinner-Nordstr$\ddot{o}$m if both...
In this work, the observed linear-polarization data of Comet Hale–Bopp are studied at wavelengths λ= 0.485 and 0.684 μm through simulations using Ballistic Particle–Cluster Aggregate Cluster–Cluster Aggregate. Using superposition t-matrix code, best-fitting values complex refractive indices calculated which can well match polarization above two wavelengths. It is found from our analysis that there not a single value monomer radius (am) simultaneously fit μm. However, for different am in...
The Thirty Meter Telescope (TMT) will be called upon to support a polarimetric observing capability. Many different programs covering range of science areas are being considered for the TMT and model overall polarization characteristics is developed. instrument development program provide means instruments developed, however telescope itself AO system must able instruments. As first step defining necessary technical requirements we have created an international working group carry out study...
The polarization introduced due to Thirty Meter Telescope (TMT) optics is calculated using an analytical model. Mueller matrices are also generated for each optical element Zemax, based on which the instrumental entire system at focal plane estimated and compared with This study significant in estimation of telescope sensitivity has great implications future instruments.
After the last apparition of comet Halley in 1985–86, a number other comets were observed polarimetry with IHW-continuum filters. From situ dust measurements Halley, size distribution functions obtained (Lamy et al. [CITE], A&A, 187, 767; Mazets Nature, 321, 276), which later used by several authors to interpret polarisation data Halley. In present work, polarimetric various have been analyzed, using Mie theory and assuming that composition particles does not differ from (Delsemme ESA...
The spherical and non-spherical dust-grain characteristics of comet Levy 1990 XX are studied in this paper. Using T-matrix theory, a good theoretical fit to the polarisation data observed by Chernova co-workers for is reported present work. calculated degree linear (p) as function scattering angle produced prolate spheroidal crystalline olivine particles with effective radius (m), variance (), aspect ratio () compatible comet's at m. After comparing above result Mie theory (m, ), it found...
Model calculations have been made to explain the polarization observed during passage of comet Austin. The observations were spread over four nights pre- and post-perihelion periods carried out at IHW interference filters. Austin data are compared with that P/Halley reported in an earlier work (Sen et al.). comparison, help Mie theory, indicates polarizations two comets probably caused by scattering due different types grains, characterized a change either complex refractive index or size...