New physical models of asteroids derived from sparse and dense photometry J. ˇ Durech (1), J. Hanuš (1), B. D. Warner (2), D. Higgins (3), J. Oey (4), F. Pilcher (5), R. D. Stephens (6), R. K. Buchheim (7), R. A. Koff (8), D. Polishook (9), V. Benishek (10), J. W. Brinsfield (11), R. I. Durkee (12), and R. Goncalves (13) (1) Astronomical Institute, Faculty of Mathematics and Physics, Charles University in Prague, Czech Republic (durech@sirrah.troja.mff.cuni.cz), (2) Palmer Divide Observatory, CO, (3) Hunters Hill Observatory, Australia, (4) Kingsgrove Observatory, Australia, (5) Organ Mesa Observatory, NM, (6) Goat Mountain Astronomical Research Station, CA, (7) Altimira Observatory, CA, (8) Antelope Hills Observatory, CO, (9) The Weizmann Institute of Science, Israel, (10) Belgrade Astronomical Observatory, Serbia, (11) Via Capote Observatory, CA, (12) Shed of Science Observatory, MN, (13) Linhaceira Observatory, Portugal Abstract We present 78 new physical models of asteroids, namely their spin vectors and rotation periods. The models were derived from the photometric data using the lightcurve inversion method. With the new mod- els, the total number of asteroid models derived from photometry has increased to ∼ 300. The new models confirm the clustering of spin vectors of small aster- oids towards the ecliptic poles [1]. 1. Introduction The lightcurve inversion method developed by [2] and [3] has led to more than 200 physical models of aster- oids derived during the past decade. The models were derived mainly from classical dense lightcurves. In re- cent years, models from combined sparse and dense photometry significantly enlarged the sample of aster- oids with know shape and rotational state. The knowl- edge of the shape, the rotation period, and the spin vec- tor of individual objects is important for revealing the distribution of spin vectors orientation in the whole as- teroid population. 2. Methods and results We used the same approach as [1] – we used archived lightcurves from the Uppsala Asteroid Photometric Catalogue [4], recent lightcurves provided by the ob- servers via the Asteroid Lightcurve Data Exchange Format 1 , and sparse photometry from selected obser- vatories downloaded from the AstDys web site. 2 We 1 http://www.minorplanet.info/alcdef.html 2 http://hamilton.dm.unipi.it/astdys/ used the lightcurve inversion method to derive unique physical models of asteroids that fit the data. We derived 78 new models that are listed in Table 1. The table lists the direction of the spin vector in eclip- tic coordinates (λ, β) and the sidereal rotation period P . In most cases, there are two pole solutions for one asteroid with roughly the same value of β and the dif- ference in λ of about 180 ◦ . The typical accuracy of the pole direction is 10 − 20 ◦ , depending on the number of observations. The accuracy of the rotation period depends on the time-span of observations and is of the order of the last decimal place of P given in Table 1. The lightcurve inversion method is capable of deriv- ing the spin axis direction and rotation period for syn- chronous binaries (1089 Tama, for example). From the modelling point of view, a fully synchronous binary behaves like a single body that can be approximated by a convex shape. The spin-axis distribution of new models confirm the results of [1], namely the concentration of spin directions of small asteroids (< 30 km) towards the high absolute ecliptic latitudes. This concentration can be explained by the YORP evolution of spin states of small asteroids. Acknowledgements The work of J. ˇ D and J.H. was supported by the grants P209/10/0537 of the Czech Science Founda- tion, GAUK 134710 of the Grant agency of the Charles University, and by the Research Program MSM0021620860 of the Ministry of Education. EPSC Abstracts Vol. 6, EPSC-DPS2011-396, 2011 EPSC-DPS Joint Meeting 2011 c  Author(s) 2011