J/A+A/627/A172 Near-Earth asteroid (1917) Cuyo opt. and IR obs. (Rozek+, 2019)
Physical model of near-Earth asteroid (1917) Cuyo from ground-based optical and
thermal-IR observations.
Rozek A., Lowry S.C., Rozitis B., Green S.F., Snodgrass C., Weissman P.R.,
Fitzsimmons A., Hicks M.D., Lawrence K.J., Duddy S.R., Wolters S.D.,
Roberts-Borsani G., Behrend R., Manzini F.
<Astron. Astrophys. 627, A172 (2019)>
=2019A&A...627A.172R 2019A&A...627A.172R (SIMBAD/NED BibCode)
ADC_Keywords: Minor planets ; Photometry, VRI ; Photometry, infrared
Keywords: minor planets, asteroids: individual: Cuyo - methods: observational -
radiation mechanisms: thermal - techniques: photometric -
techniques: spectroscopic - methods: data analysis
Abstract:
The near-Earth asteroid (1917) Cuyo was subject to radar and light
curve observations during a close approach in 1989, and observed up
until 2008. It was selected as one of our ESO Large Programme targets,
aimed at observational detections of the
Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect through long-term
light curve monitoring and physical modelling of near-Earth asteroids.
We aim to constrain the physical properties of Cuyo: shape,
spin-state, and spectroscopic & thermophysical properties of the
surface.
We acquired photometric light curves of Cuyo spanning the period
between 2010 and 2013, which we combined with published light curves
from 1989-2008. Our thermal-infrared observations were obtained in
2011. Rotationally resolved optical spectroscopy data were acquired in
2011 and combined with all available published spectra to investigate
any surface material variegation.
We developed a convex light-curve-inversion shape of Cuyo that
suggests the presence of an equatorial ridge, typical for an evolved
system close to shedding mass due to fast rotation. We determine
limits of YORP strength through light-curve-based spin-state
modelling, including both negative and positive acceleration values,
between -0.7x10-8rad/day2 and 1.7x10-8rad/day2.
Thermo-physical modelling with the ATPM provides constraints on the
geometric albedo, pV=0.24±0.07, the effective diameter
Deff=3.15±0.08km, the thermal inertia =44±9J/m2/s1/2/K, and a
roughness fraction of 0.52±0.26. This enabled a YORP strength
prediction of (-6.39±0.96)x10-10rad/day2. We also see evidence
of surface compositional variation.
The low value of YORP predicted by means of thermophysical analysis,
consistent with the results of the light curve study, might be due to
the self-limiting properties of rotational YORP, possibly involving
movement of sub-surface and surface material. This may also be
consistent with the surface compositional variation that we see. The
physical model of Cuyo can be used to investigate cohesive forces as a
way to explain why some targets survive rotation rates faster than the
fission limit.
Description:
The primary source for the optical light curve observations of Cuyo
within the ESO LP was the NTT, where the object was observed on 12
nights between April 2010 and April 2013, making a total of 11 light
curves, as the segments collected on February 5 and 6, 2013 were
folded to form a single light curve.
Additional data were obtained from the ESO 2.2m telescope (Chile)
where four light curves were gathered from February 2-21, 2012. The
ESO 2.2m telescope at La Silla is equipped with a Wide Field Imager
instrument where data is simultaneously collected on eight CCD chips,
making a mosaic image.
Further light curve data were collected at two other facilities,
including the JPL 0.6m telescope at Table Mountain Observatory (USA),
where six light curves were collected, and at the Palomar 5m (USA)
where we obtained a single light curve.
We obtained low resolution, long-slit CCD spectra of Cuyo on the night
of July 25, 2011 (UT) at the NTT. We used the EFOSC2 instrument in
spectroscopy mode.mode
We obtained additional low resolution long-slit CCD spectra of Cuyo on
the night of December 4, 2011 (UT) at the NTT.
We obtained low resolution long-slit CCD spectra of Cuyo on the night
of February 2, 2012 (UT) using the 5.1 m Hale Telescope at Palomar
Observatory with the facility Double Spectrograph mounted at the
cassegrain focus.
The optical observations were supplemented with thermal-infrared
photometry from the VISIR instrument (Lagage et al. 2004) on Unit 3
"Melipal" of the 8.2m Very Large Telescope (VLT) array at ESO's
Paranal Observatory in Chile. In particular, Cuyo was observed three
times on September 5, December 17, and December 19, 2011.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 32 2447 *Measured optical lightcurves of (1917) Cuyo used
in the shape and spin-state analysis,
including published photometry.
tablea2.dat 32 106 Measured thermal-infrared fluxes of (1917) Cuyo
using the ESO VLT with the VISIR instrument
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Note on tablea1.dat: There are 30 lightcurve segments included in the file.
Each lightcurve segment is cleary marked, along with the number of datapoints
within that lightcurve segment (e.g. "#Lightcurve 1 Datapoints 72").
Also note that there may be several nights of data in any given lightcurve
segment. (see Table 1 in paper for a details of which lightcurves are
published and the references below)
(1) Wisniewski et al., 1997, Icarus, 126, 395
(2) Velichko et al., 1989, Astronomicheskij Tsirkulyar, 1541, 35
(3) Hoffmann et al., 1993, Acta Astron., 43, 61
(4) Erikson et al., 2000, Icarus, 147, 487
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Byte-by-byte Description of file (#): tablea1.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d JD Julian Date
17 A1 --- Filter [RV] Filter
19- 25 F7.3 mag mag Relative Magnitude
28- 32 F5.3 mag e_mag 1-sigma uncertainty in relative magnitude
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 12 F12.6 d MJD Modified Julian Date (JD - 2400000.5)
15- 19 F5.2 um lambda Wavelength of IR-filter used
22- 26 F5.2 10-15W/m2/um Flux Observed IR flux (1)
29- 32 F4.2 10-15W/m2/um e_Flux Observed IR flux uncertainty (1)
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Note (1): Dates are for mid-observation and are light-time corrected.
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Acknowledgements:
Stephen Lowry, S.C.Lowry(at)kent.ac.uk
(End) Patricia Vannier [CDS] 18-Jun-2019