Where are the Mini Kreutz-family Comets?

Abstract

The Kreutz family of sungrazing comets contains over 2~000 known members, many of which are believed to be under $\sim 100$~m sizes (\textit{mini~comets}) and have only been studied at small heliocentric distances ($r_{\mathrm{H}}$) with space-based SOHO/STEREO spacecraft. To understand the brightening process of mini Kreutz comets, we conducted a survey using CFHT/MegaCam at moderate $r_{\mathrm{H}}$ guided by SOHO/STEREO observations. We identify two comets that should be in our search area but are not detected, indicating that the comets have either followed a steeper brightening rate within the previously-reported rapid brighten stage (the \textit{brightening~burst}), or the brightening burst starts earlier than expected. We present a composite analysis of pre-perihelion light-curves of five Kreutz comets that covered to $\sim 1$~AU. We observe a significant diversity in the light-curves that can be used to grossly classify them into two types: C/Ikeya-Seki and C/SWAN follow the canonical $r_{\mathrm{H}}^{-4}$ while the others follow $r_{\mathrm{H}}^{-7}$. In particular, C/SWAN seems to have undergone an outburst ($\Delta m>5$~mag) or a rapid brightening ($n\gtrsim 11$) between $r_{\mathrm{H}}=1.06$~AU to $0.52$~AU, and shows hints of structural/compositional differences compared to other bright Kreutz comets. We also find evidence that the Kreutz comets as a population lose their mass less efficiently than the dynamically new comet, C/ISON, and are relatively devoid of species that drive C/ISON's activity at large $r_{\mathrm{H}}$. Concurrent observations of C/STEREO in different wavelengths also suggest that a blue-ward species such as CN may be the main driver for brightening burst instead of previously-thought sodium.

ApJ in press

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• Evidence for a colour dependence in the size distribution of main belt asteroids

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