J/A+A/576/A18 Light curve of (2060) Chiron (Ortiz+, 2015)
Possible ring material around centaur (2060) Chiron.
Ortiz J.L., Duffard R., Pinilla-Alonso N., Alvarez-Candal A.,
Santos-Sanz P., Morales N., Fernandez-Valenzuela E., Licandro J.,
Campo Bagatin A., Thirouin A.
<Astron. Astrophys. 576, A18 (2015)>
=2015A&A...576A..18O 2015A&A...576A..18O
ADC_Keywords: Solar system ; Minor planets ; Photometry
Keywords: minor planets - asteroids: individual: (2060) Chiron -
planets and satellites: rings - techniques: imaging spectroscopy -
occultations
Abstract:
We propose that several short-duration events observed in past stellar
occultations by Chiron were produced by ring material. Some
similarities between these events and the characteristics of
Chariklo's rings could indicate common mechanisms around centaurs.
From a reanalysis of the stellar occultation data in the literature,
we determined two possible orientations of the pole of Chiron's
rings, with ecliptic coordinates λ=(352±10)°,
β=(37±10)° or λ=(144±10)°,
β=(24±10)°. The mean radius of the rings is (324±10)km.
One can use the rotational lightcurve amplitude of Chiron at different
epochs to distinguish between the two solutions for the pole. Both
solutions imply a lower lightcurve amplitude in 2013 than in 1988,
when the rotational lightcurve was first determined. We derived
Chiron's rotational lightcurve in 2013 from observations at the 1.23m
CAHA telescope, and indeed its amplitude was smaller than in 1988. We
also present a rotational lightcurve in 2000 from images taken at the
CASLEO 2.15m telescope that is consistent with our predictions. Out
of the two poles, the λ=(144±10)°, β=(24±10)°
solution provides a better match to a compilation of rotational
lightcurve amplitudes from the literature and those presented here. We
also show that using this preferred pole orientation, Chiron's
long-term brightness variations are compatible with a simple model
that incorporates the changing brightness of the rings while the tilt
angle with respect to the Earth is changing with time. Also, the
variability of the water ice band in Chiron's spectra as seen in the
literature can be explained to a large degree by an icy ring system
whose tilt angle changes with time and whose composition includes
water ice, analogously to the case of Chariklo. We present several
possible formation scenarios for the rings from qualitative points of
view and speculate on why rings might be common in centaurs. We also
speculate on whether the known bimodal color distribution of the
centaurs could be due to centaurs with rings and centaurs without
rings.
Description:
Photometry results for the CAHA and CASLEO observations, respectively.
In this sample table we list the Julian date (JD, corrected for light
time), the Relative magnitude (Rel. Mag in magnitudes) and the 1sigma
error associated (Err. in magnitude), topocentric (delta) and
heliocentric (r_h) distances (both distances expressed in AU) and the
solar phase angle, in degrees.
object.dat :
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Code Name H i e a
mag deg AU
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2060 Chiron 6.10 6.938408 0.38209890 13.63836652
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 48 223 Photometry results for the CAHA and CASLEO
observations
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See also:
J/AJ/107/1814 : Chiron occultations (Bus+, 1994)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 F13.5 d JD Julian Date
15- 20 F6.3 mag Rmag [-0.08/0.08] Relative magnitude
22- 26 F5.3 mag e_Rmag [0.007/0.06] rms uncertainty on Rmag
28- 33 F6.3 AU Delta [10/17] Geocentric distance Δ
35- 40 F6.3 AU rh [10/18] Heliocentric distance
42- 46 F5.3 deg alpha [1.1/5.7] Solar phase angle α
48 I1 --- Obs [1/4] Period of observation (1)
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Note (1): column added at CDS, corresponds to:
1 = night 26/27-Aug-2000 (JD2451783)
2 = night 28/29-Aug-2000 (JD2451785)
3 = 09-Oct-2013 (JD2456575)
4 = 10-Oct-2013 (JD2456576)
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Acknowledgements:
Rene Duffard, duffard(at)iaa.es
(End) Patricia Vannier [CDS] 29-Jan-2015