Photometry and models of selected main belt asteroids: VIII. Low-pole asteroids

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, λp1 = 58°, βp1 = + 16°; λp2 = 242°, βp2 = + 4°; (174) Phaedra - P = 5.750249 h, λp = 265°, βp = + 5°; (679) Pax - P = 8.456016 h, λp1 = 42°, βp1 = -5°; λp2 = 220°, βp2 = + 32° (pole 2 preferred after comparison with AO-resolved observations); (714) Ulula - P = 6.998376 h, λp1 = 42°, βp1 = -9°; λp2 = 227°, βp2 = -14°. Conclusions. This work suggests that asteroid spin axes do not avoid the ecliptic plane, contrary to what the classical modelling suggested. © 2011 ESO.