Large Super-Fast Rotator Hunting Using the Intermediate Palomar Transient Factory

TL;DR

This study used the Intermediate Palomar Transient Factory to identify large super-fast rotators among asteroids, discovering one new candidate and analyzing their physical properties and distribution, revealing insights into their internal cohesion and rarity.

Contribution

First dedicated survey to find large super-fast rotators using the Palomar Transient Factory, discovering a new candidate and analyzing their physical and spin-rate properties.

Findings

Discovered one new large super-fast rotator, (40511) 1999 RE88.

Large super-fast rotators require internal cohesive strength of ~780 Pa.

Their cohesive strengths range from 100 to 1000 Pa, similar to lunar regolith.

Abstract

In order to look for large super-fast rotators, five dedicated surveys covering ~ 188 square degree in the ecliptic plane have been carried out in R-band with ~10 min cadence using the intermediate Palomar Transient Factory in late 2014 and early 2015. Among 1029 reliable rotation periods obtained from the surveys, we discovered one new large super-fast rotator, (40511) 1999 RE88, and other 18 candidates. (40511) 1999 RE88 is an S-type inner main-belt asteroid with a diameter of D = 1.9 +- 0.3 km, which has a rotation period of P = 1.96 +- 0.01 hr and a lightcurve amplitude of ~0.1 mag. To maintain such fast rotation, an internal cohesive strength of ~780 Pa is required. Combining all known large super-fast rotators, their cohesive strengths all fall in the range of 100 to 1000 Pa of lunar regolith. However, the number of large super-fast rotators seems to be far less than the whole asteroid population. This might indicate a peculiar asteroid group for them. Although the detection efficiency for a long rotation period is greatly reduced due to our two-day observation time span, the spin-rate distributions of this work show consistent results with Chang et al. (2015) after considering the possible observational bias in our surveys. It shows a number decrease with increase of spin rate for asteroids with diameter of 3 < D < 15 km, and a number drop at spin-rate of f = 5 rev/day for asteroids with D < 3 km.