Analysis of the rotation period of asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger – search for the YORP effect

Abstract

Context. The spin state of small asteroids can change on a long timescale by the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, the net torque that arises from anisotropically scattered sunlight and proper thermal radiation from an irregularly-shaped asteroid. The secular change in the rotation period caused by the YORP effect can be detected by analysis of asteroid photometric lightcurves. Aims. We analyzed photometric lightcurves of near-Earth asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger with the aim to detect possible deviations from the constant rotation caused by the YORP effect. Methods. We carried out new photometric observations of the three asteroids, combined the new lightcurves with archived data, and used the lightcurve inversion method to model the asteroid shape, pole direction, and rotation rate. The YORP effect was modeled as a linear change in the rotation rate in time dω/dt. Values of dω/dt derived from observations were compared with the values predicted by theory. Results. We derived physical models for all three asteroids. We had to model Eger as a nonconvex body because the convex model failed to fit the lightcurves observed at high phase angles. We probably detected the acceleration of the rotation rate of Eger dω/dt = (1.4 ± 0.6) × 10 −8 rad d −2 (3σ error), which corresponds to a decrease in the rotation period by 4.2 ms yr −1 . The photometry of Cerberus and Ra-Shalom was consistent with a constant-period model, and no secular change in the spin rate was detected. We could only constrain maximum values of |dω/dt| < 8 × 10 −9 rad d −2 for Cerberus, and |dω/dt| < 3 × 10 −8 rad d −2 for Ra-Shalom.Key words. minor planets, asteroids: individual: (1865) Cerberus -minor planets, asteroids: individual: (2100) Ra-Shalomminor planets, asteroids: individual: (3103) Eger -methods: data analysis -techniques: photometric Tables 1-3 are available in electronic form at

Compact YORP formulation and stability analysis

“…For the last three of these more stable ones, the YORP effect has been observed directly from lightcurves (Kaasalainen et al 2007;Durech et al 2008Durech et al , 2012. The stability estimate is consistent with the good correspondence between the computed and observed YORP acceleration for Apollo and Geographos.…”

Optical observations of NEA 3200 Phaethon (1983 TB) during the 2017 apparition

“…However, the features are not obviously matched with our non-convex model. Apparently, the non-convex model contains many details that may lead to misinterpretation (Durech et al 2012). Because the RMS of the convex model is low (about 30% in chi-square), we adopt the convex model as a pole solution for Phaethon.…”

“…Recently, a number of works for the reconstruction of a non-convex model have been conducted giving weight to various sources (i.e. adaptive optics, lightcurve, and stellar occultation) (see Hanuš et al 2017;Viikinkoski et al 2017 (Durech et al 2012). Its non-convex shape model better fits the lightcurves that were observed at large phase angles than a convex one.…”

A Martian origin for the Mars Trojan asteroids

“…Observational studies have shown that the YORP effect can double the spin rate of an asteroid in a relatively short timescale of about a million to 10 million years for a km-sized (D=1 km) near-Earth (a=1 AU) asteroids 42,43,44,45,46 . For a Mars Trojan, located at a semi-major axis of a=1.5 AU, with a diameter D=2 km, dω/dt should decrease by (1.5/1) 2 (2/1) 2 ~ 10, which sets the τ YORP at 10 to 100 million years, at least an order of magnitude smaller than the dynamical age of the Eureka cluster, giving sufficient time for Eureka to spin-up beyond the spin limit due to the YORP effect and to shed mass.…”