2017AJ....154..173K

We present an optical and near-infrared (hereafter NIR) polarimetric study of a comet C/2013 US10 (Catalina) observed on UT 2015 December 17-18 at phase angles of α = 52.°1-53.°1. Additionally, we obtained an optical spectrum and multi-band images to examine the influence of gas emission. We find that the observed optical signals are significantly influenced by gas emission; that is, the gas-to-total intensity ratio varies from 5 to 30% in the R_C and 3%-18% in the I_C bands, depending on the position in the coma. We derive the "gas-free dust polarization degrees" of 13.8% ± 1.0% in the R_C and 12.5% ± 1.1% in the I_C bands and a gray polarimetric color, i.e., -8.7% ± 9.9% µm^–1 in optical and 1.6% ± 0.9% µm^–1 in NIR. The increments of polarization obtained from the gas correction show that the polarimetric properties of the dust in this low-polarization comet are not different from those in high-polarization comets. In this process, the cometocentric distance dependence of polarization has disappeared. We also find that the R_C-band polarization degree of the southeast dust tail, which consists of large dust particles (100 µm-1 mm), is similar to that in the outer coma where small and large ones are mixed. Our study confirms that the dichotomy of cometary polarization does not result from the difference of dust properties, but from depolarizing gas contamination. This conclusion can provide a strong support for similarity in origin of comets.