Photometry and models of selected main belt asteroids

VIII. Low-pole asteroids^⋆,⋆⋆

¹ Astronomical Observatory, Adam Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
e-mail: aniab@lab.astro.amu.edu.pl
² Geneva Observatory, 1290 Sauverny, Switzerland
³ Les Engarouines Observatory, 84570 Mallemort-du-Comtat, France
⁴ Collonges Observatory, 90 allée des résidences, 74160 Collonges, France
⁵ “Le Florian”, Villa 4, 880 chemin de Ribac-Estagnol, 06600 Antibes, France
⁶ AUDE Association (User association of electronic detectors) Paris, France
⁷ Agrupación Astronómica de Sabadell, Apartado de Correos 50, PO Box 50, 08200 Sabadell, Barcelona, Spain
⁸ l’Observatoire de Cabris, 408 chemin Saint Jean Pape, 06530 Cabris, France
⁹ Stazione Astronomica di Sozzago, 28060 Sozzago, Italy
¹⁰ Blauvac Observatory, 84570 St-Estève, France
¹¹ N. Copernicus Astronomical Centre, Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw, Poland
¹² Forte Software, Os. Jagiełły 28/28 60-685 Poznań, Poland
¹³ Ludick Observatory, Krugersdorp, South Africa

Received: 8 July 2010
Accepted: 16 February 2011

Abstract

Context. The set of more than 100 asteroids, for which spin parameters have been modelled using an amplitude, magnitude or epoch methods, showed a pronounced gap in the distribution of the asteroid spin axes. These spin axes are rarely aligned with the ecliptic plane.

Aims. The number of asteroids with known spin parameters should be increased to allow for statistical investigations.

Methods. We gathered extensive photometric datasets on four selected main-belt asteroids to model their spin and shape parameters using the lightcurve inversion method. Our only criterion of selection was their observability for small telescopes.

Results. All four of the modelled asteroids happened to have rotational poles that lie close to the ecliptic plane (periods and J2000 north pole coordinates): (94) Aurora    −    P = 7.226191 h, λ_p1 = 58°, β_p1 =  + 16°; λ_p2 = 242°, β_p2 =  + 4°; (174) Phaedra    −    P = 5.750249 h, λ_p = 265°, β_p =  + 5°; (679) Pax − P = 8.456016 h, λ_p1 = 42°, β_p1 = −5°; λ_p2 = 220°, β_p2 =  + 32° (pole 2 preferred after comparison with AO-resolved observations); (714) Ulula − P = 6.998376 h, λ_p1 = 42°, β_p1 = −9°; λ_p2 = 227°, β_p2 = −14°.

Conclusions. This work suggests that asteroid spin axes do not avoid the ecliptic plane, contrary to what the classical modelling suggested.