Do Slivan states exist in the Flora family?: II. Fingerprints of the Yarkovsky and YORP effects

Authors:

• Agnieszka Kryszczyńska

Abstract

Context. It is known that the Yarkovsky effect moves small astroids to larger/smaller semimajor axes depending on their prograde/retrograde spins. The YORP effect influences asteroid spin periods and spin axis orientations so that they evolve in time. The alignment of the spin vectors and correlations of the spin rates, now known as Slivan states and observed among members of the Koronis family, are interpreted in terms of the YORP effect and spin-orbit resonances. Splitting asteroid families into prograde and retrograde groups has recently been proposed as a result of the Yarkovsky effect. Prograde and retrograde asteroids drift in different directions, and this has never been observed directly. Aims. The influence of the Yarkovsky and YORP effects should be observable among objects in asteroid families, especially in the Flora family, which lies close to the Sun and consists of many small objects. Methods. The Flora family asteroids were modelled using the lightcurve inversion technique. As a result the orientation of spin vectors, shapes, and sidereal periods of rotation were obtained. Results. Results of modelling of the Flora family asteroids show the family splitting into prograde and retrograde groups as a result of the Yarkovsky effect. The observed ratio between prograde and retrograde asteroids is 2.6. The positions of spin vectors, as well as their similar latitudes suggest, that the Slivan states are observed among the Flora family asteroids. Conclusions. The influence of the Yarkovsky and YORP effect is clearly visible in the Flora family. The location of the Flora family close to the ν₆ resonance explains the lack of retrograde objects and confirms the excess of retrograde rotators among NEAs and their origin from the ν₆. The Slivan states that I searched seem to be present among prograde rotators in this family even though they were not expected. © ESO, 2013.