An imaging polarimeter (IMPOL) for multi-wavelength observations

Ramaprakash, A. N.; Gupta, Ranjan; Sen, A. K.; Tandon, S. N.

doi:10.1051/aas:1998148

Cited by 61 publications

(52 citation statements)

References 15 publications

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“…P is the fraction of linear polarization and θ is the angle of polarization plane. Correction factor for nonuniform responsivity of (i) CCD pixels and (ii) system to orthogonal polarized beams, is also introduced as a ratio described by Ramaprakash et al (1998),…”

Section: Polarimetrymentioning

confidence: 99%

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Photometric and polarimetric observations of fast declining Type II supernovae 2013hj and 2014G

Bose

Kumar

Misra

et al. 2015

Mon. Not. R. Astron. Soc.

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We present broadband photometric and polarimetric observations of two type II supernovae (SNe) 2013hj and 2014G. SN 2014G is a spectroscopically classified type IIL event, which we also confirm photometrically as its light curve show characteristic features (plateau slope of 2.55 mag (100 d) −1 in V -band and duration of ∼ 77d) of a generic IIL SN. On the other hand SN 2013hj also shows high plateau decline rate of 1.5 mag (100 d) −1 in V -band, similar to SNe IIL, but marginally lower than SNe IIL template light curves. Our high cadence photometric observations of SNe 2013hj and 2014G enables us to cover all characteristic phases up to radioactive tail of optical light curves. Broadband polarimetric observations reveal some polarization in SN 2013hj with subtle enhancement as SN evolves towards plateau end, however the polarization angle remains constant throughout the evolution. This characteristic is consistent with the idea that the evolving SN with recombining hydrogen envelope is slowly revealing more asymmetric central region of explosion. Modelling of bolometric light curve yields a progenitor mass of ∼ 11M ⊙ with a radius of ∼ 700R ⊙ for SN 2013hj, while for SN 2014G model estimated progenitor mass is ∼ 9M ⊙ with a radius of ∼ 630R ⊙ , both having a typical energy budget of ∼ 2 × 10 51 erg.

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Section: Polarimetrymentioning

confidence: 99%

“…In principle, a single set of q and u value is sufficient to determine polarization parameters, but all four stokes parameters are used as a redundancy check. The errors associated with stokes parameters are dominated primarily by photon statistics and is expressed as (Ramaprakash et al 1998),…”

Section: Polarimetrymentioning

confidence: 99%

Photometric and polarimetric observations of fast declining Type II supernovae 2013hj and 2014G

Bose

Kumar

Misra

et al. 2015

Mon. Not. R. Astron. Soc.

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“…Two successive positions of the half-wave plate are needed to retrieve the degree of polarization and the position angle of the polarization vector. More details on the principles of the instrument are described in Ramaprakash et al (1998). When the half-wave plate rotates successively 22.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Polarimetric observations of comet 67P/Churyumov-Gerasimenko during its 2008–2009 apparition

Hadamcik

Sen²,

Levasseur-Regourd

et al. 2010

A&A

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Context. Remote observations of the light scattered by comet 67P/Churyumov-Gerasimenko dust coma are of major importance for determining the physical properties of the particles and prepare the rendezvous with the ESA/Rosetta spacecraft in 2014. Aims. Light scattering and especially linear polarization observations allow comparison between different coma regions and different comets, including comets that have been studied by space probes. Our aim is to retrieve physical properties of the dust particles and to characterize their evolution around perihelion passage. Results. The decrease in intensity as a function of the distance to nucleus in log-log scale is on average close to −1, although important variations with values down to −1.5 are noticed, in agreement with previous observations in 1982−83 and 1995−96. The intensity along the tailward direction decreases with a slope between −1.2 two months before perihelion (2009 February 28) to −1.0 two months after perihelion, and the decrease is more pronounced in the sunward direction. Before perihelion, aperture polarization values are comparable to polarization values measured on other comets at similar phase angles. The sharp decrease in intensity and the feature in the tailward direction, without any difference in polarization in the coma before perihelion, could suggest the presence of large dark particles. The post-perihelion increase in intensity and in polarization suggests that an outburst has occurred. The freshly ejected dust polarizes more the scattered light and is more sensitive to the solar radiation pressure, suggesting small micron-or submicron-sized grains. Conclusions. Polarization and intensity variations in the coma of 67P/Churyumov-Gerasimenko are reminiscent of those noticed for some comets such as comet 81P/Wild 2 and comet 9P/Tempel 1. The presence of rather large particles can thus be suggested before and just after perihelion and the ejection of post-perihelion smaller grains, eventually in fluffy aggregates. A strong seasonal effect related to the obliquity of the comet suggests that the different grains originate in different hemispheres of the nucleus.

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“…The polarimetric accuracies are limited by photon noise. (for details please see Sen & Tandon 1994;Ramaprakash et al 1998).…”

Section: Observation Instrumentation and Data Reductionmentioning

confidence: 99%

Imaging polarimetry of some selected dark clouds

Sen

Gupta²,

Ramaprakash³

et al. 2000

Astron. Astrophys. Suppl. Ser.

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Abstract.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, to produce polarization map of the Bok Globules. The stars in the field, which are mostly background to the cloud show typically 2% of linear polarization. Clouds which are less dynamic (having 12 CO 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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An imaging polarimeter (IMPOL) for multi-wavelength observations

Cited by 61 publications

References 15 publications

Photometric and polarimetric observations of fast declining Type II supernovae 2013hj and 2014G

Photometric and polarimetric observations of fast declining Type II supernovae 2013hj and 2014G

Polarimetric observations of comet 67P/Churyumov-Gerasimenko during its 2008–2009 apparition

Imaging polarimetry of some selected dark clouds

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