Photometric Study Of 28978 Ixion At Small Phase Angle

Discovered in 2001, the Kuiper Belt Object 28978 Ixion belongs to the dynamical class of Plutinos. Because of its brightness (R magnitude about 19.5) it has been extensively studied, its diameter and albedo being estimated by Spitzer to be about 570 km and 15% (Stansberry et al., 2008). Absorption feature of cristalline water ice has been detected (Merlin et al., 2010) and negative linear polarisation has been measured (Boehnhardt et al., 2004). So far no lightcurve nor phase curve at very small phase angle has been published, the only information being that the lightcurve amplitude was inferior to 0.15 magnitude (Ortiz et al., 2003). We present new photometric observations obtained with the 3.5-m telescope NTT at the European Southern Observatory with broad band filters (B, V, R and I). These observations permit to derive a rotation period of 15.9+/-0.5 hr (if a single-peaked lightcurve is assumed) with a peak to peak amplitude of 0.06+/-0.03 magnitude. The phase curve does not reveal any bright opposition surge even for very small phase angle (α=0.02 deg). When our data are combined with the one of Boehnhardt et al. (up to α=1.34 deg) a linear fit provides a slope of 0.201+/-0.014 mag/deg.

References :

Boehnhardt H., Bagnulo S., Muinonen K. et al., 2004, A&A 415, L21-L25

Merlin F., Barucci M.A., de Bergh C. et al., 2010, Icarus 208, 945-954

Ortiz J.L., Gutiérrez P.J., Casanova V., Sota A., 2003, A&A 407, 1149-1155

Stansberry J., Grundy W., Brown M. et al., 2008, The Solar System Beyond Neptune, Univ. of Arizona Press, pp161-179