J/A+A/548/A12 67P/Churyumov-Gerasimenko R-band light curve (Lowry+, 2012)
The nucleus of comet 67P/Churyumov-Gerasimenko. A new shape model and
thermophysical analysis.
Lowry S., Duddy S.R., Rozitis B., Green S.F., Fitzsimmons A., Snodgrass C.,
Hsieh H.H., Hainaut O.
<Astron. Astrophys. 548, A12 (2012)>
=2012A&A...548A..12L 2012A&A...548A..12L
ADC_Keywords: Comets ; Photometry
Keywords: methods: data analysis - techniques: photometric -
comets: individual: 67P/Churyumov-Gerasimenko -
infrared: planetary systems
Abstract:
Comet 67P/Churyumov-Gerasimenko is the target of the European Space
Agency Rosetta spacecraft rendez-vous mission. Detailed physical
characteristation of the comet before arrival is important for mission
planning as well as providing a test bed for ground-based observing
and data-analysis methods.
To conduct a long-term observational programme to characterize the
physical properties of the nucleus of the comet, via ground-based
optical photometry, and to combine our new data with all available
nucleus data from the literature.
We applied aperture photometry techniques on our imaging data and
combined the extracted rotational lightcurves with data from the
literature. Optical lightcurve inversion techniques were applied to
constrain the spin state of the nucleus and its broad shape. We
performed a detailed surface thermal analysis with the shape model and
optical photometry by incorporating both into the new Advanced
Thermophysical Model (ATPM), along with all available Spitzer 8-24um
thermal-IR flux measurements from the literature.
A convex triangular-facet shape model was determined with axial ratios
b/a=1.239 and c/a=0.819. These values can vary by as much as 7% in
each axis and still result in a statistically significant fit to the
observational data. Our best spin state solution has
Psid=12.76137±0.00006 hrs, and a rotational pole orientated at
Ecliptic coordinates lambda=78°(±10°),
beta=+58°(±10°). The nucleus phase darkening behaviour was
measured and best characterized using the IAU HG system. Best fit
parameters are: G=0.11±0.12 and HR(1,1,0)=15.31±0.07. Our shape
model combined with the ATPM can satisfactorily reconcile all optical
and thermal-IR data, with the fit to the Spitzer 24um data taken in
February 2004 being exceptionally good. We derive a range of
mutually-consistent physical parameters for each thermal-IR data set,
including effective radius, geometric albedo, surface thermal inertia
and roughness fraction.
The overall nucleus dimensions are well constrained and strongly imply
a broad nucleus shape more akin to comet 9P/Tempel 1, rather than the
highly elongated or `bilobed' nuclei seen for comets 103P/Hartley 2 or
8P/Tuttle. The derived low thermal inertia of <15J/m2/K/s1/2 is
comparable with that measured for other comets scaled to similar
heliocentric distances, and implies a surface regolith finer than
lunar surface material.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 39 93 Photometry derived from our NTT data sets
(see Section 2 of paper)
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See also:
B/comets : Database of the orbital elements of comets (Rocher, 2007)
J/A+A/520/A92 : Comet 67P global plasma parameter simulation (Gortsas+, 2011)
J/A+A/527/A113 : 67P/Churyumov-Gerasimenko R-band light curve (Tubiana+, 2011)
object.dat :
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Code Name Elem q e i H1
d AU deg mag
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67P P/Churyumov-Gerasimenko 2454890.5 1.2465141 0.6401757 7.040861 11.63
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 13 F13.5 d JD Julian Date
16 A1 --- Filt [RV] Filter type
19- 24 F6.3 mag Rmag Apparent magnitude, mR (1)
27- 32 F6.3 mag RMAG Absolute Magnitude, mR(11alpha)
35- 39 F5.3 mag e_Rmag 1-sigma uncertainty in magnitudes
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Note (1): Each magnitude data point was typically obtained by combining 6-12
individual sidereally-tracked 100s exposures. Actual number of R-filter
images taken and processed was 276 in May 2005, and 201 in July 2007.
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Acknowledgements:
Stephen Lowry, S.C.Lowry(at)kent.ac.uk
(End) Patricia Vannier [CDS] 19-Oct-2012