New photometric observations of asteroids (1862) Apollo and (25143) Itokawa – an analysis of YORP effect
Astronomical Institute, Charles University in Prague, V Holešovičkách 2, 18000 Prague, Czech Republic e-mail: email@example.com
2 Department of Mathematics and Statistics, Rolf Nevanlinna Institute, PO Box 68, 00014 University of Helsinki, Finland
3 Science Division, Jet Propulsion Laboratory, 4800 Oak Grove Drive, MS 183-301, Pasadena, CA 91109, USA
4 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721-0092, USA
5 Hunters Hill Observatory, 7 Mawalan Street, Ngunnawal ACT 2913, Australia
6 Institute of Astronomy of Kharkiv National University, Sumska str. 35, Kharkiv 61022, Ukraine
7 Crimean Astrophysical Observatory, Simeiz 98680, Ukraine
8 Korea Astronomy & Space Science Institute, 61-1 Hwa-am Dong, Yuseong Gu, Daejon 305-348, South Korea
9 Palmer Divide Observatory, Colorado Springs, Colorado 80908, USA
10 Ulugh Beg Astronomical Institute, Uzbek Academy of Sciences, Astronomicheskaya 33, Tashkent 100052, Uzbekistan
11 Keldysh Institute of Applied Mathematics, RAS, Miusskaya sq. 4, Moscow 125047, Russia
12 Astronomical Observatory, Adam Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
13 Department of Earth and Planetary Science, The University of Tokyo, Bynkyo-ku, Tokyo 113-0033, Japan
Accepted: 18 May 2008
Aims. Asteroid (1862) Apollo is one of two asteroids in which the YORP effect was detected. We carried out new photometric observations of Apollo in April 2007 to enlarge the time line and to derive a more precise shape and spin state model. We also observed another YORP-candidate, asteroid (25143) Itokawa, in December 2006 and January 2007 to obtain a longer time line. An estimation of the YORP strength on Itokawa based on its precise shape model from the Hayabusa mission predicted the deceleration to be already observable during the 2007 apparition.
Methods. We used the lightcurve inversion method to model the shape and spin state of Apollo. For Itokawa, the shape and pole direction are known to a high degree of accuracy from the Hayabusa mission, so we used a modified version of lightcurve inversion with only two free parameters – the rotation period and its linear change in time.
Results. The new model of Apollo confirms earlier results. The observed acceleration of Apollo's rotation rate is , which is in agreement with the theoretically predicted value. For Itokawa, the theoretical YORP value is sensitive to the resolution of the shape model and lies in the range from -2 to . This is inconsistent with results of lightcurve inversion that place an upper limit to the change of Itokawa's rotation rate ∼.
Key words: minor planets, asteroids / methods: data analysis / techniques: photometric
© ESO, 2008