Abstract
ABSTRACT We present results derived from the first multi-chord stellar occultation by the trans-Neptunian object (229762) 2007 UK126, observed on 2014 November 15. The event was observed by the Research and Education Collaborative Occultation Network project and International Occultation Timing Association collaborators throughout the United States. Use of two different data analysis methods obtain a satisfactory fit to seven chords, yielding an elliptical fit to the chords with an equatorial radius of km and equivalent radius of km. A circular fit also gives a radius of km. Assuming that the object is a Maclaurin spheroid with indeterminate aspect angle, and using two published absolute magnitudes for the body, we derive possible ranges for geometric albedo between and , and for the body oblateness between and . For a nominal rotational period of 11.05 hr, an upper limit for density of ρ = 1740 kg m−3 is estimated for the body.
Highlights
Trans-Neptunian objects (TNOs) are remnants of a collisionally and dynamically evolved planetesimal disk in the outer solar system
We present results derived from the 2014 November 15 stellar occultation by this body
Six sites from Research and Education Collaborative Occultation Network (RECON), one International Occultation Timing Association (IOTA) site located in Urbana, Illinois, and two telescopes at San Pedro Martir acquired data, for a total of seven positive detections of the event and two negative chords at San Pedro Martir, which were located more than 500 km south of the shadow path (Figure 1)
Summary
Since the TNO is near the limit of the critical range to be a Maclaurin object, we can consider two possibilities: (1) all the timings are correct within 1σ uncertainty, implying that 2007 UK126 is compatible with a Maclaurin object and has large topographic features (craters or mountains) of the order of 10 s of kilometers (a possible solution, considering the New Horizons images on Charon that shows topographic features as big as +/−6 km Nimmo et al.2016) or (2) 2007 UK126 is a smooth (no topographic features) Maclaurin object, implying that timing problems are present at some stations With this in mind, we have allowed time shifts for all stations, aligning the middles of all chords, resulting in a value of 1.37 and a radial rms of 16 km, i.e., without significant improvement of the fit quality. For the MWB analysis, the conversion from video data to a light curve does not present any intrinsic timing errors beyond limitations imposed by the low signal-to-noise ration for the event (Section 3.1.2)
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