Optical and Near-Infrared Polarimetry for a Highly Dormant Comet 209P/LINEAR

Abstract

We conducted an optical and near-infrared polarimetric observation of the highly dormant Jupiter-Family Comet, 209P/LINEAR. Because of its low activity, we were able to determine the linear polarization degrees of the coma dust particles and nucleus independently, that is $P_n$=30.3${}_{-0.9}^{+1.3}$% at $\hat{I}\pm$=92.2${}^{\circ }$ and $P_n$=31.0${}_{-0.7}^{+1.0}$% at $\hat{I}\pm$=99.5${}^{\circ }$ for the nucleus, and $P_c$=28.8${}_{-0.4}^{+0.4}$% at $\hat{I}\pm$=92.2${}^{\circ }$ and 29.6${}_{-0.3}^{+0.3}$% at $\hat{I}\pm$=99.5${}^{\circ }$ for the coma. We detected no significant variation in $P$ at the phase angle coverage of 92.2${}^{\circ }$-99.5${}^{\circ }$, which may imply that the obtained polarization degrees are nearly at maximum in the phase-polarization curves. By fitting with an empirical function, we obtained the maximum values of linear polarization degrees $P_{\max }$=30.8% for the nucleus and $P_{\max }$=29.6% for the dust coma. The $P_{\max }$ of the dust coma is consistent with those of dust-rich comets. The low geometric albedo of $P_v$=0.05 was derived from the slope-albedo relationship and was associated with high $P_{\max }$. We examined $P_{\max }$-albedo relations between asteroids and 209P, and found that the so-called Umov law seems to be applicable on this cometary surface.

27 pages, 7 figures, accepted on 2015 October 14 for publication in the Astrophysical Journal