Physical properties of the trans-Neptunian object (38628) Huya from a multi-chord stellar occultation

Abstract

Context. As part of our international program aimed at obtaining accurate physical properties of trans-Neptunian objects (TNOs), we predicted a stellar occultation by the TNO (38628) Huya of the star Gaia DR2 4352760586390566400 (mG = 11.5 mag) on March 18, 2019. After an extensive observational campaign geared at obtaining the astrometric data, we updated the prediction and found it favorable to central Europe. Therefore, we mobilized half a hundred of professional and amateur astronomers in this region and the occultation was finally detected by 21 telescopes located at 18 sites in Europe and Asia. This places the Huya event among the best ever observed stellar occultation by a TNO in terms of the number of chords. Aims. The aim of our work is to determine an accurate size, shape, and geometric albedo for the TNO (38628) Huya by using the observations obtained from a multi-chord stellar occultation. We also aim to provide constraints on the density and other internal properties of this TNO. Methods. The 21 positive detections of the occultation by Huya allowed us to obtain well-separated chords which permitted us to fit an ellipse for the limb of the body at the moment of the occultation (i.e., the instantaneous limb) with kilometric accuracy. Results. The projected semi-major and minor axes of the best ellipse fit obtained using the occultation data are (a′, b′) = (217.6 ± 3.5 km, 194.1 ± 6.1 km) with a position angle for the minor axis of P′ = 55.2° ± 9.1. From this fit, the projected area-equivalent diameter is 411.0 ± 7.3 km. This diameter is compatible with the equivalent diameter for Huya obtained from radiometric techniques (D = 406 ± 16 km). From this instantaneous limb, we obtained the geometric albedo for Huya (pV = 0.079 ± 0.004) and we explored possible three-dimensional shapes and constraints to the mass density for this TNO. We did not detect the satellite of Huya through this occultation, but the presence of rings or debris around Huya was constrained using the occultation data. We also derived an upper limit for a putative Pluto-like global atmosphere of about psurf = 10 nbar.

Physical properties of the trans-Neptunian object (38628) Huya from a multi-chord stellar occultation

“…Since the ellipse fit is not linear in the parameters, an estimate of the error in the parameters using a χ 2 minimization technique may result in an underestimation of the errors. Therefore, we estimated the uncertainties in the five parameters of the fitted ellipse using a Monte Carlo approach, as done in Santos-Sanz et al (2021). We randomly generated the 37 chord extremities 10 4 times, meeting the requirements provided by their corresponding uncertainties.…”

“…If this is true, the chords centers must be aligned (see, e.g. Braga-Ribas et al 2013;Santos-Sanz et al 2021). For completeness, and to check if this solution is very different from the original one we slightly shift the chords by performing a linear fit to the centers of the chords and looking for the ellipse that best fits these chords.…”

“…We can constrain the presence of rings (or debris) around Huya using the light curves obtained during the occultation (e.g. Braga-Ribas et al 2014;Ortiz et al 2017;Sickafoose et al 2019;Santos-Sanz et al 2021).…”

Earth-based Stellar Occultation Predictions for Jupiter, Saturn, Uranus, Neptune, Titan, and Triton: 2023–2050

“…The Centaur (2060) Chiron exhibits outgassing behavior (Ruprecht et al 2015) and possibly hosts a ring system (Sickafoose et al 2020). Over the last decade, ambitious international observing campaigns have yielded the surprising discoveries of rings around the Centaur (10199) Chariklo (Braga-Ribas et al 2014;Bérard e al., 2017;Morgado et al 2021), dwarf planet (136108) Haumea (Ortiz et al 2017), and trans-Neptunian object (TNO) (50000) Quaoar (Morgado et al 2023;Pereira et al 2023), and have begun to provide accurate physical properties of TNOs themselves (Souami et al 2020;Santos-Sanz et al 2022a;Fernández-Valenzuela et al 2023). The availability of highly accurate star positions provided by Gaia (Gaia Collaboration et al 2021;Gaia Collaboration 2022) has revolutionized the observing strategy for small-target occultations by enabling portable telescopes to be placed along the path of the occultation shadow.…”

Reaching Submillisecond Accuracy in Stellar Occultations and Artificial Satellite Tracking

“…The image was taken with SharpCap with an exposure time of 50 μs. In the live view of SharpCap, vertically moving light patterns (related to Figure5) within individual NEXTA LED sections indicate the presence of the rolling shutter.The literature shows that the camera is used to record stellar occultations(Santos-Sanz et al 2022;Vara-Lubiano et al 2022), although, unlike the QHY174M-GPS, additional timing…”