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

¹ Astronomical Institute, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 18000 Prague, Czech Republic
e-mail: durech@sirrah.troja.mff.cuni.cz
² Astronomical Observatory of Taras Shevshenko National University, Astronomichna str. 3, Kiev, Ukraine
³ Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
⁴ Ulugh Beg Astronomical Institute, Uzbek Academy of Sciences, Astronomicheskaya 33, Tashkent 100052, Uzbekistan
⁵ Sonoita Research Observatory, 1442 E Roger Rd, Tuscon, AZ 85719, USA
⁶ Physics and Astronomy Department, Appalachian State University, Boone, NC 28608, USA
⁷ Crimean Astrophysical Observatory, Simeiz Department, Simeiz 98680, Ukraine
⁸ Kharadze Abastumani Astrophysical Observatory, Ilia State University, G.Tsereteli str. 3, Tbilisi 0162, Georgia
⁹ Department of Mathematics, Tampere University of Technology, PO Box 553, 33101 Tampere, Finland
¹⁰ Institute of Astronomy of Kharkiv National University, Sumska str. 35, Kharkiv 61022, Ukraine
¹¹ The Central (Pulkovo) Astronomical Observatory of the Russian Academy of Sciences, Pulkovskoye chaussee 65/1, St.-Petersburg 196140, Russia
¹² University of California at Berkeley, Department of Astronomy, 601 Campbell Hall, Berkeley, CA 94720, USA
¹³ Carl Sagan Center, SETI institute, 189 Bernardo Av., Mountain View CA 94043, USA
¹⁴ Keldysh Institute of Applied Mathematics, RAS, Miusskaya sq. 4, 125047 Moscow, Russia
¹⁵ Kingsgrove Observatory, 23 Monaro Ave., Kingsgrove, NSW, Australia
¹⁶ Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁷ Ondřejov Observatory, AV ČR, 251 65 Ondřejov, Czech Republic
¹⁸ Konkoly Observatory of the Hungarian Academy of Sciences, PO Box 67, 1525 Budapest, Hungary
¹⁹ Goat Mountain Astronomical Research Station, 11355 Mount Johnson Court, Rancho Cucamonga, CA 91737, USA
²⁰ Department of Experimental Physics, University of Szeged, Dóm tér 9, 6720 Szeged, Hungary
²¹ Institut de Mécanique Céleste et de Calcul des Éphémérides, Observatoire de Paris, UMR8028 CNRS, 77 Av. Denfert-Rochereau, 75014 Paris, France
²² Palmer Divide Observatory, 17955 Bakers Farm Rd., Colorado Springs, CO 80908, USA
²³ ELTE Gao-Lendület Research Group, 9700 Szombathely, Hungary

Received: 12 April 2012
Accepted: 5 September 2012

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.