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Imaging polarimetry of some selected dark clouds

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 different nights during the period December 1997 and April 1998. The CCD images obtained from the instrument (IMPOL) were analyzed...

Intermittency and multiscale dynamics in milling of fiber reinforced composites

We have analyzed the variations in cutting force during milling of a fiber-reinforced composite material. In particular, we have investigated the multiscale dynamics of the cutting force measured at different spindle speeds using multifractals and wavelets. The multifractal analysis revealed the changes in complexity with varying spindle speeds. The wavelet analysis identified...

RETRACTED ARTICLE: Liquid filtration and particle concentration using a cross-flow filter for microfluidics applications

, University of Southampton , Southampton SO14 3ZH, UK 2 A. K. Sen (&) Department of Mechanical Engineering, Indian Institute of Technology Guwahati , Guwahati 781039, Assam, India

Modelling the polarization properties of Comet 1P/Halley using a mixture of compact and aggregate particles

Both the in situ measurement of Comet 1P/Halley and the Stardust-returned samples of Comet Wild 2 showed the presence of a mixture of compact and aggregate particles, with both silicates and organic refractory being in the composition of the cometary dust. Results obtained recently from the Stardust mission suggest that the overall ratio of compact to aggregate particles is 65:35...

Photopolarimetric study of the star-forming clouds CB3, CB25, and CB39

Context. The small compact isolated dark clouds also known as “Bok globules” are believed to be ideal sites for low-mass star formation. Some of these clouds are undergoing gravitational collapse, and the ambient magnetic field plays a key role in collapse dynamics. The background star polarimetry is generally accepted as a good tool to map the magnetic field, which is...

Photopolarimetric study of the star-forming clouds CB3, CB25, and CB39

Context. The small compact isolated dark clouds also known as “Bok globules” are believed to be ideal sites for low-mass star formation. Some of these clouds are undergoing gravitational collapse, and the ambient magnetic field plays a key role in collapse dynamics. The background star polarimetry is generally accepted as a good tool to map the magnetic field, which is...

Optical and submillimetre observations of Bok globules – tracing the magnetic field from low to high density

We present optical and submillimetre polarimetry data of the Bok globule CB3. We also present optical polarimetry and submillimetre continuum data of the Bok globule CB246. We use each set of polarimetry data to infer the magnetic field orientation in each of the clouds. The optical data can only trace the field orientation in the low-density edge regions of clouds, because if...

Aggregate dust model to describe polarization properties of Comet Hale–Bopp

H. S. Das 0 S. R. Das 0 A. K. Sen 0 0 Department of Physics, Assam University , Silchar 788011 , India A B S T R A C T In this work, the observed linear-polarization data of Comet Hale-Bopp are

Polarimetric studies of comet Levy 1990 XX

A&A Astronomy & Astrophysics H. S. Das 1 A. K. Sen 0 0 Department of Physics, Assam University , Silchar 788011, Assam , India 1 Department of Physics, Karimganj College , Karimganj 788710, Assam

Aggregate model of cometary dust: an application to comet Levy 1990XX

In the present work, the light-scattering properties of comet Levy 1990XX are studied through simulations using Ballistic Particle-Cluster Aggregation (BPCA) or Ballistic Cluster–Cluster Aggregation (BCCA) aggregates of up to 128 spherical monomers of different compositions (e.g. silicates, carbonaceous materials etc.) and the best-fitting theoretical polarization curve is...

An analysis of the distribution of background star polarization in dark clouds

The polarization observed for stars behind dark clouds (Bok globules) is often used as a diagnostic to study the ongoing star formation processes in these clouds. Such polarization maps in the optical have been reported for eight nearby clouds, CB3, CB25, CB39, CB52, CB54, CB58, CB62 and CB246, in our previous work. With a view to understanding the origin of this polarization, in...

The polarimetric properties of cometary dust and a possible effect of dust aging by the Sun

After the last apparition of comet Halley in 1985–86, a number of other comets were observed in polarimetry with IHW-continuum filters. From the in situ dust measurements of Halley, dust size distribution functions were obtained (Lamy et al. [CITE], A&A, 187, 767; Mazets et al. [CITE], Nature, 321, 276), which were later used by several authors to interpret polarisation data of...

Instrumental polarization caused by telescope optics during wide field imaging

When astronomical observations are made for a celestial object, with non -zero field angle (wrt telescope axis), the beam of parallel rays from the celestial object strikes the telescope mirror obliquely. Each unpolarized ray of light when it strikes the metal coated mirror surface gets polarized due to reflection. On the contrary, when the field angle is zero, these reflected...

Instrumental polarization caused by telescope optics during wide field imaging

When astronomical observations are made for a celestial object, with non -zero field angle (wrt telescope axis), the beam of parallel rays from the celestial object strikes the telescope mirror obliquely. Each unpolarized ray of light when it strikes the metal coated mirror surface gets polarized due to reflection. On the contrary, when the field angle is zero, these reflected...

Imaging polarimetry of some selected dark clouds

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 different nights during the period December 1997 and April 1998. The CCD images obtained from the instrument (IMPOL) were analyzed...

Imaging polarimetry of some selected dark clouds

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 different nights during the period December 1997 and April 1998. The CCD images obtained from the instrument (IMPOL) were analyzed...

Imaging polarimetry of some selected dark clouds

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 different nights during the period December 1997 and April 1998. The CCD images obtained from the instrument (IMPOL) were analyzed...

On the periodicity of the basic component of solar ultraviolet flux

The Fourier integral of solar UV flux over the time domain shows a periodicity of 90 days when the contribution due to the sunspot component is subtracted from the experimentally observed flux values. When the effect of sunspots on the UV flux is not eliminated, however, the frequency spectrum resembles that found by previous authors.

Polarimetric properties of comet Austin

Model calculations have been made to explain the polarization observed during the passage of comet Austin. The observations were spread over four nights during the pre- and post-perihelion periods and were carried out at the IHW interference filters. The Austin data are compared with that of comet P/Halley reported in an earlier work (Sen et al.). The comparison, with the help of...