J/A+A/670/A52 (65) Cybele VLT/SPHERE disk-resolved images (Marsset+, 2023)
The equilibrium shape of (65) Cybele: primordial or relic of a large impact?
Marsset M., Broz M., Vermersch J., Rambaux N., Ferrais M., Viikinkoski M.,
Hanus J., Jehin E., Podlewska-Gaca E., Bartczak P., Dudzinski G., Carry B.,
Vernazza P., Szakats R., Duffard R., Jones A., Molina D., Santana-Ros T.,
Benkhaldoun Z., Birlan M., Dumas C., Fetick R., Fusco T., Jorda L.,
Marchis F., Vachier F., Yang B.
<Astron. Astrophys. 670, A52 (2023)>
=2023A&A...670A..52M 2023A&A...670A..52M (SIMBAD/NED BibCode)
ADC_Keywords: Solar system ; Minor planets ; Morphology ; Optical
Keywords: methods: observational - techniques: high angular resolution -
planets and satellistes individual: (65) Cybele
Abstract:
Cybele asteroids constitute an appealing reservoir of primitive
material genetically linked to the outer Solar System, and the
physical properties (size and shape) of the largest members can be
readily accessed by large (8m class) telescopes.
We took advantage of the bright apparition of the most iconic member
of the Cybele population, (65) Cybele, in July and August 2021 to
acquire high-angular-resolution images and optical light curves of the
asteroid with which we aim to analyse its shape and bulk properties.
Eight series of images were acquired with VLT/SPHERE+ZIMPOL, seven of
which were combined with optical light curves to reconstruct the shape
of the asteroid using the ADAM, MPCD, and SAGE algorithms. The origin
of the shape was investigated by means of N-body simulations.
Cybele has a volume-equivalent diameter of 263±3km and a bulk
density of 1.55±0.19g/cm3. Notably, its shape and rotation state
are closely compatible with those of a Maclaurin equilibrium figure.
The lack of a collisional family associated with Cybele and the higher
bulk density of that body with respect to other large P-type asteroids
suggest that it never experienced any large disruptive impact followed
by rapid re-accumulation. This would imply that its present-day shape
represents the original one. However, numerical integration of the
long-term dynamical evolution of a hypothetical family of Cybele shows
that it is dispersed by gravitational perturbations and chaotic
diffusion over gigayears of evolution.
The very close match between Cybele and an equilibrium figure opens up
the possibility that D≥260km (M≥1.5x1019kg) small bodies from the
outer Solar System all formed at equilibrium. However, we cannot
currently rule out an old impact as the origin of the equilibrium
shape of Cybele. Cybele itself is found to be dynamically unstable,
implying that it was "recently" (<1Gyr ago) placed on its current
orbit either through slow diffusion from a relatively stable orbit in
the Cybele region or, less likely, from an unstable,
Jupiter-family-comet orbit in the planet-crossing region.
Description:
We obtained 70 images of Cybele at 7 epochs in 2021 using
VLT/SPHERE/ZIMPOL. All images were reduced and deconvolved following
the procedure described in Vernazza et al. (2018A&A...618A.154V 2018A&A...618A.154V).
objects:
----------------------------------------------------------------
Planet Name H Diam i e a
mag km deg AU
-------------------------------------------------------------------
65 Cybele 6.92 263 3.567994 0.116080 3.4390432
-------------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 202 70 VLT/SPHERE disk-resolved images obtained in the
N_R filter with the ZIMPOL camera
fits/* . 140 Individual fits images
--------------------------------------------------------------------------------
See also:
J/A+A/618/A154 : (89) Julia SPHERE/ZIMPOL images (Vernazza+, 2018)
J/A+A/619/L3 : (16) Psyche images (Viikinkoski+, 2018)
J/A+A/623/A6 : Vesta VLT/SPHERE/ZIMPOL images (Fetick+, 2019)
J/A+A/623/A132 : (41) Daphne SPHERE/ZIMPOL images (Carry+, 2019)
J/A+A/624/A121 : (7) Iris Deconvolved disk-resolved images (Hanus+, 2019)
J/A+A/633/A65 : (704) Interamnia images (Hanus+, 2020)
J/A+A/638/L15 : (16) Psyche. VLT/SPHERE images & shape models (Ferrais+, 2020)
J/A+A/641/A80 : (31) Euphrosyne R-band images (Yang+, 2020)
J/A+A/650/A129 : (87) Sylvia SPHERE images (Carry+, 2021)
J/A+A/653/A57 : (216) Kleopatra images (Marchis+, 2021)
J/A+A/662/A71 : (22) Kalliope images (Ferrais+, 2022)
http://astro.troja.mff.cuni.cz/projects/asteroids3D/web.php : DAMIT Home Page
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 "datime" Obs.date Observation date (UT)
21- 23 I3 s Exp Exposure time (1)
25- 28 F4.2 --- Airmass Airmass
30- 33 F4.2 AU Delta Distance to the Earth
35- 38 F4.2 AU r Distance to the Sun
40- 43 F4.1 deg alpha Phase angle
45- 49 F5.3 arcsec Da Angular diameter
51- 55 F5.1 deg lambdasubE Sub-Earth point longitude
57- 60 F4.1 deg betasubE Sub-Earth point latitude
62- 69 A8 --- Cam Camera
71-135 A65 --- FileName1 Deconvolved fits image filename in
subdirectory fits
137-202 A66 --- FileName2 Reduced fits images filename in
subdirectory fits
--------------------------------------------------------------------------------
Note (1): The total exposure time of 240 s corresponds to 1.1% of the rotation
period or 4 in the rotation phase.
--------------------------------------------------------------------------------
Acknowledgements:
Michael Marsset, mmarsset(at)eso.org
(End) Patricia Vannier [CDS] 24-Nov-2022