Analysis of a double star occultation by TNO (470316) 2007 OC10

Transneptunian objects (TNOs) are some of the most pristine objects in the Solar System. These remnants from the protoplanetary disk of planetesimals have been barely altered since the formation of the Solar System. Hence, they are ideal to test formation and evolutionary models. The technique of stellar occultations consists on observing the flux drop of a star as an object passes in front of it. If several observers at different locations on Earth observe the event, the projected bidimensional shape at the moment of the occultation can be reconstructed with spatial resolution only matched by that of in-situ space missions. Therefore, stellar occultations represent an excellent oportunity to probe the shape distribution in the transneptunian region. This is of great interest since three-dimensional shapes provide insight into internal structure, composition and densities [1].

In case of an occultation of a double star, stellar occultations also enable us to resolve the double star and determine individual magnitudes with unparalleled precision. However, the analysis of (unresolved) double star occultations can be challenging. Complex correlations might arise between the relative positions of the stars and the shape parameters. Moreover, if there is a considerable apparent brightness difference and photometry is low in SNR, it is difficult to distinguish between the detection of the dim star being occulted (possitive detection) and no occultation (negative detection). A Bayesian approach is optimal in such cases [2], since no a priori assumptions need to be made about the positive or negative nature of the light curve. Each flux value from each site is considered as an individual data point to be compared against the predicted value by the model for some parameter values. In addition, this method enables us to better understand possible correlations between parameters. Such a methodology has recently been used in published occultation analysis with satisfactory results [3, 4].

(470316) 2007 OC10 is a scattered disk object, i.e. an object that is being currently scattered by Neptune, resulting in high orbital eccentricity and inclination. I will present the preliminary results from an occultation by this TNO recorded on the 2022-08-22. The observed flux drop from different locations is consistent with an occultation of double star. We modeled the possible relative positions and magnitude difference between both stars and the projected shape of 2007 OC10 (assuming an elliptical limb) with a Bayesian approach. Preliminary analysis of the data yields a star separation of ~ 60 mas and magnitude difference of ~ 1.2 mag. The fit to the projected shape enabled us to derive an albedo of ~15 % and an area equivalent radius of ~ 150 km. There are only two published TNO occultation of a double star, by 2014 WC510 [4] and by 2003 VS2 (in which case only the bright star was considered in the analysis) [5].

I would like to acknowledge the effort of all the observers of the occultation event.

References: [1] Rambaux, Baguet, Chambat et al. 2017, ApJL, 850.1-pg L9; [2] Leiva 2022, 16th EPSC2022-669; [3] Strauss, Leiva, Keller et al. 2021, PSJ, 2.1-pg 22; [4] Leiva, Buie, Keller et al. 2019, Planet. Sci. J., 1.2-pg 48; [5] Benedetti-Rossi, Santos-Sanz, Ortiz et al. 2019, AJ, 158.4-pg. 159