Do Slivan states exist in the Flora family?

I. Photometric survey of the Flora region^⋆

¹ Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
e-mail: agn@amu.edu.pl
² Institut de Mécanique Céleste et Calcul des Éphémérides, Observatoire de Paris, 77 Av. Denfert Rochereau, 75014 Paris, France
³ Institute of Astronomy, Bulgarian Academy of Sciences Tsarigradsko Chausse 72, 1784 Sofia, Bulgaria
⁴ Faculty of Natural Sciences, Cyril and Methodius University Skopje, Macedonia
⁵ Institute of Astronomy, Karazin National University, Kharkov, Ukraine
⁶ Astrophysics Division, Institute of Physics, Jan Kochanowski University, Świetokrzyska 15, 25-406 Kielce, Poland
⁷ San Pedro de Atacama Observatory, Chile
⁸ Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon, France
⁹ Geneva Observatory, 1290 Sauverny, Switzerland
¹⁰ Institut de Recherche en Astrophysique et Planétologie (IRAP), Université de Toulouse, 9 avenue du colonel Roche, 31028 Toulouse Cedex 4, France
¹¹ Observatoire de Haute-Provence, 04870 Saint Michel l’ Observatoire, France
¹² Observatoire des Engarouines, 84570 Mallemort-du-Comtat, France
¹³ Stazzione Astronomica di Sozzago, 28060 Sozzago, Italy
¹⁴ Le Cres Observatory, Rue des Écoles 2, 34920 Le Cres, France
¹⁵ Bedoin Observatory, Avignon, France
¹⁶ Department of Physics, PO Box 64, 00014 University of Helsinki, Finland
¹⁷ Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Santa Cruz de Tenerife, Spain

Received: 27 March 2012
Accepted: 23 June 2012

Abstract

Context. Recent studies have uncovered evidence that the statistical properties of asteroids’ physical parameters are a fundamental source of information on the physics of their collisions and evolution. The analysis of the spin rates and spin vector distributions helps us to understand the role of various known and new effects. The alignment of spin vectors and the correlation of spin rates are for the first time observed for ten members of the Koronis family. These unexpected non-random orientations of the spin axes and correlations of the spin rates, now known as Slivan states are interpreted in terms of a YORP effect and spin-orbit resonances.

Aims. To study non-gravitational-effects, there appears to be a need for new observational campaigns devoted to determining the physical parameters of the asteroid families.

Methods. We analysed the photometric observations of the asteroids, which are the most efficient method of studying asteroid physical parameters.

Results. We report the results of a ten-year long observational survey of the light variations of objects in the Flora region. We present 544 individual lightcurves of 55 objects obtained at various observing geometries. These lightcurves yield new or refined synodic periods for 32 asteroids and confirm period determinations for 23 objects in our sample. To improve the statistics of the Flora family objects, we add to our dataset 91 objects with reliably determined periods. The distribution of rotation rates for the Flora family is non-Maxwellian at a confidence level of 94% and different from those of the Koronis and the Hungaria families. It seems to be consistent with the long-term influence of the YORP effect, although it is also indicative of a younger age for the Flora family compared to both the Koronis and the Hungaria families.

Conclusions. Our new data is a foundation for the spin vector and shape determinations that will be the objectives of the second paper of the series. We search for spin vector and spin periods correlations in order to determine whether Slivan states exist in the Flora family.