The rotational light curve of (79360) SilaNunam, an eclipsing binary in the Kuiper Belt
Abstract
We combine longterm photometric observations in multiple band passes to determine the rotational light curve for the binary KuiperBelt object (79360) SilaNunam. We measure an unambiguous fundamental period of 6.2562 ± 0.002 d, within 0.02% of half the orbital period (P_{orb} = 12.50995 ± 0.00036 d) determined earlier from HST observations resolving the binary. The light curve is doublepeaked, and well fit by the sum of two sinusoids: a primary with period P_{orb}/2 and peaktopeak amplitude 0.120 ± 0.012 mag and a secondary with period P_{orb} and peaktopeak amplitude 0.044 ± 0.010 mag. Excluding observations within ∼0.1 deg of opposition, we measure a linear solar phase dependence with slope 0.147 ± 0.018 mag deg^{1} and a mean absolute magnitude in the Gunn g band of 6.100 ± 0.006 mag. There is no rotational color variation exceeding 4%. We also observe that eclipses occur centered on light curve minima to within 0.3%, requiring the long axis of at least one of the two bodies to point precisely toward the other. Assuming the binary is doubly synchronous and both rotation axes are aligned with the orbital angular momentum vector, our observations jointly constrain triaxial shape models for Sila and Nunam such that the product of their longtointermediate axes ratios is 1.120 ± 0.01. Hence both bodies are elongated by 6%, or else one is elongated by 612%, and the other by less than 6%.
 Publication:

Icarus
 Pub Date:
 July 2014
 DOI:
 10.1016/j.icarus.2014.03.046
 arXiv:
 arXiv:1404.0244
 Bibcode:
 2014Icar..236...72R
 Keywords:

 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 doi:10.1016/j.icarus.2014.03.046