18 research outputs found
A large topographic feature on the surface of the trans-Neptunian object (307261) 2002 MS measured from stellar occultations
This work aims at constraining the size, shape, and geometric albedo of the
dwarf planet candidate 2002 MS4 through the analysis of nine stellar
occultation events. Using multichord detection, we also studied the object's
topography by analyzing the obtained limb and the residuals between observed
chords and the best-fitted ellipse. We predicted and organized the
observational campaigns of nine stellar occultations by 2002 MS4 between 2019
and 2022, resulting in two single-chord events, four double-chord detections,
and three events with three to up to sixty-one positive chords. Using 13
selected chords from the 8 August 2020 event, we determined the global
elliptical limb of 2002 MS4. The best-fitted ellipse, combined with the
object's rotational information from the literature, constrains the object's
size, shape, and albedo. Additionally, we developed a new method to
characterize topography features on the object's limb. The global limb has a
semi-major axis of 412 10 km, a semi-minor axis of 385 17 km, and
the position angle of the minor axis is 121 16. From
this instantaneous limb, we obtained 2002 MS4's geometric albedo and the
projected area-equivalent diameter. Significant deviations from the fitted
ellipse in the northernmost limb are detected from multiple sites highlighting
three distinct topographic features: one 11 km depth depression followed by a
25 km height elevation next to a crater-like depression with an
extension of 322 39 km and 45.1 1.5 km deep. Our results present an
object that is 138 km smaller in diameter than derived from thermal
data, possibly indicating the presence of a so-far unknown satellite. However,
within the error bars, the geometric albedo in the V-band agrees with the
results published in the literature, even with the radiometric-derived albedo
Physical properties of the trans-Neptunian object (38628) Huya from a multi-chord stellar occultation
Within our international program to obtain 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.) for
March 18, 2019. After an extensive observational campaign, we updated the
prediction and it turned out to be favorable to central Europe. Therefore, we
mobilized half a hundred professional and amateur astronomers, and the
occultation was finally detected from 21 telescopes located at 18 sites. This
makes the Huya event one of the best ever observed stellar occultation by a TNO
in terms of the number of chords. We determine accurate size, shape, and
geometric albedo, and we also provide constraints on the density and other
internal properties of this TNO. 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. 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 of the
minor axis P' = 55.2 9.1 degrees. 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 (p = 0.079 0.004) and we explored possible 3D
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 is constrained using the occultation data. We also derived an upper
limit for a putative Pluto-like global atmosphere of about p = 10
nbar.Comment: Accepted for publication in Astronomy & Astrophysics (30-April-2022).
19 pages, 7 figure