Linear and circular polarization of comet C/2009 P1 (Garradd)

S V Kolesnikov,S V Zaitsev,N N Kiselev,V K Rosenbush,V L Afanasiev,D N Shakhovskoy

doi:10.5047/eps.2013.05.014

Abstract

We report measurements of linear and circular polarization for the recent comet C/2009 P1 (Garradd) during its approach to the Earth in 2011–2012. Aperture photoelectric observations were carried out on July 29, 2011-April 22, 2012 in the R and WR wide-band filters at the 2.6-m telescope of the Crimean Astrophysical Observatory (Ukraine). Spectropolarimetric measurements of linear polarization in the range 3800–8000 A and imaging circular polarimetry in the comet continuum filter (λ0 = 6840/90 A) were also carried out with the SCORPIO-2 focal reducer at the 6-m telescope of the Special Astrophysical Observatory (Russia) on February 2-April 21, 2012. The degree of polarization of light scattered by comet Garradd changes from −2.2 ± 0.2% to 4.9 ± 0.2% at phase angles 13.7° and 35.9°, respectively. These values are in a good agreement with those for dusty comets at the respective phase angles. Left-handed (negative) circular polarization of comet Garradd in the continuum filter was identified. The values of Pc vary noticeably over the coma in the range from −0.03 to −0.08% and from −0.05 to −0.3% on February 14 and April 21, respectively. These results confirm our previous conclusion that the observed circular polarization for comets is predominantly left-handed.

Highlights

Polarimetry is a powerful tool for probing the physical properties of cometary dust particles; see numerous examples in Mishchenko et al (2010) and references therein
Observatory on February 2–April 21, 2012. These were the first measurements of cometary polarization ever attempted with this telescope and this instrument, so we describe these measurements in more detail
This figure displays the value of linear polarization Pr = 4.9 ± 0.2% obtained from spectropolarimetric observations of the comet at the 6-m BTA telescope on February 2, 2012

Summary

Introduction

Polarimetry is a powerful tool for probing the physical properties of cometary dust particles; see numerous examples in Mishchenko et al (2010) and references therein. One of the ways of studying the properties of cometary dust is a comparison of the polarization phase angle dependence for different comets.

Results

Conclusion