The multichord stellar occultation on 2019 October 22 by the trans-Neptunian object (84922) 2003 VS${}_2$

Abstract

We predicted, observed, and analyzed the multichord stellar occultation of the Second Gaia Data Release (Gaia DR2) source 3449076721168026624 (m${}_v$ = 14.1 mag) by the plutino object 2003 VS${}_2$ (hereafter, VS${}_2$) on 2019 October 22. We also carried out photometric observations to derive the rotational light curve amplitude and rotational phase of VS${}_2$ during the stellar occultation. Combining the results and assuming a triaxial shape, we derived the 3D shape of VS${}_2$. Out of the 39 observatories involved in the observational campaign, 12 sites reported a positive detection; this makes it one of the best observed stellar occultations by a TNO so far. We obtained a rotational light curve amplitude of $\Delta$m = 0.264 $\pm$ 0.017 mag, a mean area-equivalent diameter of D${}_{A_{eq}}$ = 545 $\pm$ 13 km, and a geometric albedo of 0.134 $\pm$ 0.010. The best triaxial shape obtained for VS${}_2$ has semiaxes a = 339 $\pm$ 5 km, b = 235 $\pm$ 6 km, and c = 226 $\pm$ 8 km. The derived aspect angle is $\theta$ = 59$°\pm$ 2$°$ or its supplementary $\theta$ = 121$°\pm$ 2$°$, depending on the north-pole position. The spherical-volume equivalent diameter is D${}_{V_{eq}}$ = 524 $\pm$ 7 km. If we consider large albedo patches on its surface, the semi-major axis of the ellipsoid could be ~10 km smaller. These results are compatible with the previous ones determined from the single-chord 2013 and four-chord 2014 stellar occultations and with the effective diameter and albedo derived from Herschel and Spitzer data. They provide evidence that VS${}_2$'s 3D shape is not compatible with a homogeneous triaxial body in hydrostatic equilibrium, but it might be a differentiated body and/or might be sustaining some stress. No secondary features related to rings or material orbiting around VS${}_2$ were detected.

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• Betelgeuse, the Prototypical Red Supergiant
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• Size and shape of the trans-Neptunian object (470316) 2007 OC10: Comparison with thermal data