YORP and Yarkovsky effects in asteroids (1685) Toro, (2100) Ra-Shalom, (3103) Eger, and (161989) Cacus

Abstract

The rotation states of small asteroids are affected by a net torque arising from an anisotropic sunlight reflection and thermal radiation from the asteroids' surfaces. On long timescales, this so-called YORP effect can change asteroid spin directions and their rotation periods. We analyzed lightcurves of four selected near-Earth asteroids with the aim of detecting secular changes in their rotation rates that are caused by YORP. We use the lightcurve inversion method to model the observed lightcurves and include the change in the rotation rate $\mathrm{d}\omega /\mathrm{d}t$ as a free parameter of optimization. We collected more than 70 new lightcurves. For asteroids Toro and Cacus, we used thermal infrared data from the WISE spacecraft and estimated their size and thermal inertia. We also used the currently available optical and radar astrometry of Toro, Ra-Shalom, and Cacus to infer the Yarkovsky effect. We detected a YORP acceleration of $\mathrm{d}\omega /\mathrm{d}t=(1.9\pm 0.3)\times 10^{-8}\mathrm{rad}{\mathrm{d}}^{-2}$ for asteroid Cacus. For Toro, we have a tentative ($2\sigma$) detection of YORP from a significant improvement of the lightcurve fit for a nonzero value of $\mathrm{d}\omega /\mathrm{d}t=3.0\times 10^{-9}\mathrm{rad}{\mathrm{d}}^{-2}$. For asteroid Eger, we confirmed the previously published YORP detection with more data and updated the YORP value to $(1.1\pm 0.5)\times 10^{-8}\mathrm{rad}{\mathrm{d}}^{-2}$. We also updated the shape model of asteroid Ra-Shalom and put an upper limit for the change of the rotation rate to $|\mathrm{d}\omega /\mathrm{d}t|\lesssim 1.5\times 10^{-8}\mathrm{rad}{\mathrm{d}}^{-2}$. Ra-Shalom has a greater than $3\sigma$ Yarkovsky detection with a theoretical value consistent with observations assuming its size and/or density is slightly larger than the nominally expected values.

References in corpus (6)

• Formation of asteroid pairs by rotational fission
• Star catalog position and proper motion corrections in asteroid astrometry
• Asteroids' physical models from combined dense and sparse photometry and scaling of the YORP effect by the observed obliquity distribution
• Tangential component of the YORP effect
• A 3-dimensional model of tangential YORP
• The thermal emission from boulders on (25143) Itokawa and general implications for the YORP effect

Cited by in corpus (12)

• The solar nebula origin of (486958) Arrokoth, a primordial contact binary in the Kuiper belt
• Solar System Physics for Exoplanet Research
• A $75\%$ Occurrence Rate of Debris Discs around F stars in the $\beta$ Pic Moving Group
• Detection of the YORP Effect on the contact-binary (68346) 2001 KZ66 from combined radar and optical observations
• The crater-induced YORP effect
• Shape model and rotation acceleration of (1685) Toro and (85989) 1999 JD6 from optical observations
• Physical properties of near-Earth asteroid (2102) Tantalus from multi-wavelength observations
• Improved models for near-Earth asteroids (2100) Ra-Shalom, (3103) Eger, (12711) Tukmit & (161989) Cacus
• Light-curve analysis and shape models of NEAs 7335, 7822, 154244 and 159402
• Recent arrivals to the main asteroid belt
• Spin Parameters and Shape Models of Near-Earth Asteroids (4660) Nereus, (21088) Chelyabinsk, (66146) 1998 TU3, and (297418) 2000 SP43
• Observed tidal evolution of Kleopatra's outer satellite