Imaging polarimetry and photometry of comet 21P/Giacobini-Zinner

Abstract

We report results of our polarimetric observations of comet 21P/Giacobini-Zinner made at phase angles, α ≈ 76-78°, between 10 and 17 of September, 2018, and compare them with previous measurements. We find significant variations in the polarimetric signals that appear consistent with those reported previously. These variations and subsequent modeling suggest that the particles in the coma are replenished within a period of approximately one day. This period is significantly shorter for highly absorbing carbonaceous particles than for non-absorbing Mg-rich silicate particles. Such a difference in the relative abundances of these components can lead to variations in the polarization response of the coma. The strong positive polarization in the subsolar direction suggests a large relative abundance of carbonaceous material, which may be an indicator of jet-type activity.

Monitoring polarization in comet 46P/Wirtanen

“…We repeated measurements for 12 full cycles of the analyzer rotation; only observations on January 12 of 2019 were interrupted after 10 cycles by quickly changing weather conditions. A detailed log of the observations is given in Table 1. Three rotations of the analyzer through 60° provide data sufficient for computation of the Stokes parameters I, Q, and U (e.g., Chornaya et al, 2020a and references therein), fully characterizing the linear polarization in a comet. In particular, one can compute a total degree of linear polarization I U Q P / 2 2 + = and angle θ 0 of the plane of linear polarization with respect to the first analyzer position (i.e., 0°; see, e.g., Chornaya et al, 2020a for more details).…”

“…A detailed log of the observations is given in Table 1. Three rotations of the analyzer through 60° provide data sufficient for computation of the Stokes parameters I, Q, and U (e.g., Chornaya et al, 2020a and references therein), fully characterizing the linear polarization in a comet. In particular, one can compute a total degree of linear polarization I U Q P / 2 2 + = and angle θ 0 of the plane of linear polarization with respect to the first analyzer position (i.e., 0°; see, e.g., Chornaya et al, 2020a for more details). While choice of the first position could be arbitrary, in what follows, the angle θ 0 can be converted to the angle between the polarization plane and the scattering plane, which we denote with θ.…”

“…All three comets were observed using the same telescope, standard stars, and data-reduction technique. We, therefore, omit their description here and refer to Chornaya et al (2020a) for further observational details.…”

Resolving color differences of comet 41P/Tuttle-Giacobini-Kresák

“…As a model of cometary dust particles, we use the agglomerated debris particles, whose fluffy and irregular morphology appears to be in good quantitative accordance with what was detected in situ in micron-sized dust particles in comets (see, e.g., Zubko et al 2016;Chornaya et al 2020). At the top of Fig.…”

“…Dust in comets is composed of numerous components with different chemical and mineralogical compositions. The color slope in some comets also suggests the presence of materials with a noticeable wavelength dependence on their refractive index m (Zubko et al 2015b;Ivanova et al 2017b;Luk'yanyk et al 2019;Chornaya et al 2020). Laboratory measurements of the refractive index in only a few presumable analogs of cometary-dust constituent materials are available in the literature (e.g., Duley 1984;Warren 1984;Khare et al 1990Khare et al , 1993Jenniskens 1993;Dorschner et al 1995).…”