Polarimetry, photometry, and spectroscopy of comet C/2009 P1 (Garradd)

We present the results of photometry, linear spectropolarimetry, and imaging circular polarimetry of comet C/2009 P1 (Garradd) performed at the 6-m telescope BTA of the Special Astrophysical Observatory (Russia) equipped by the multi-mode focal reducer SCORPIO-2. The comet was observed at two epochs post-perihelion: on February 2-14, 2012 at rh∼1.6 au and α∼36°; and on April 14-21, 2012 at rh∼2.2 au and α∼27° The spatial maps of the relative intensity and circular polarization as well as the spectral distribution of linear polarization are presented. There were two features (dust and gas tails) oriented in the solar and antisolar directions on February 2 and 14 that allowed us to determine rotation period of the nucleus as 11.1 ± 0.8 hours. We detected emissions of C2, C3, CN, CH, NH2 molecules as well as CO+ and H2O+ ions, along with a high level of the dust continuum. On February 2, the degree of linear polarization in the continuum, within the wavelength range of 0.67-0.68 µm, was about 5 ± 0.2% in the near-nucleus region up to ∼6000 km and decreased to about 3 ± 0.2% at ∼40,000 km. After correction for the continuum contamination, the inherent degree of polarization in the emission band C2 (Δν= 0) is about 3.3%. We detected a small increase of linear polarization with the wavelength with the spectral gradient ΔP/Δλ=+ 4 ± 0.8%/µm and ΔP/Δλ=+ 6.2 ± 1.3%/µm, respectively, on February 2 and April 14. Linear polarization indicates that this dust-rich comet can be attributed to the high-Pmax comets. The left-handed (negative) circular polarization at the level approximately from −0.06 ± 0.02% to −0.4 ± 0.02% was observed at the distances up to 3 ×104 km from the nucleus on February 14 and April 21, respectively.