J/A+A/603/A87 Local production rates of 67P/CG from MIRO (Marshall+, 2017)
Spatially resolved evolution of the local H2O production rates of comet
67P/Churyumov-Gerasimenko from the MIRO instrument on Rosetta.
Marshall D.W., Hartogh P., Rezac L., von Allmen P., Biver N.,
Bockelee-Morvan D., Crovisier J., Encrenaz P., Gulkis S., Hofstadter M.,
Ip W.-H., Jarchow C., Lee S., Lellouch E.
<Astron. Astrophys. 603, A87 (2017)>
=2017A&A...603A..87M 2017A&A...603A..87M (SIMBAD/NED BibCode)
ADC_Keywords: Comets ; Spectroscopy
Keywords: comets: individual: 67P/Churyumov-Gerasimenko -
submillimetre: general - techniques: spectroscopic
Abstract:
Using spectroscopic and continuum data measured by the MIRO instrument
on board Rosetta of comet 67P/Churyumov-Gerasimenko, it is possible to
derive and track the change in the water production rate, to learn how
the outgassing evolves with heliocentric distance. The MIRO data are
well suited to investigate the evolution of 67P, in unprecedented
spatial and temporal detail.
To obtain estimates of the local effective Haser production rates we
developed an efficient and reliable retrieval approach with
precalculated lookup tables. We employed line area ratios
(H216O/H218O) from pure nadir observations as the key
variable, along with the Doppler shift velocity, and continuum
temperature. This method was applied to the MIRO data from August 2014
until April 2016. Perihelion occurred on August 13, 2015 when the
comet was 1.24AU from the Sun.
During the perihelion approach, the water production rates increased
by an order of magnitude, and from the observations, the derived
maximum for a single observation on August 29, 2015 is
(1.42±0.51)x1028. Modelling the data indicates that there is an
offset in the peak outgassing, occurring 34±10 days after
perihelion. During the pre-perihelion phase, the production rate
changes with heliocentric distance as rh-3.8±0.2; during post-
perihelion, the dependence is rh-4.3±0.2. The comet is
calculated to have lost 0.12±0.06% of its mass during the perihelion
passage, considering only water ice sublimation. Additionally, this
method provides well- sampled data to determine the spatial
distribution of outgassing versus heliocentric distance. The time
evolution is definitely not uniform across the surface. Pre- and
post-perihelion, the surface temperature on the southern hemisphere
changes rapidly, as does the sublimation rate with an exponent of ~-6.
There is a strong latitudinal dependence on the rh exponent with
significant variation between northern and southern hemispheres, and
so the average over the comet surface may only be of limited
importance. We present more detailed regional variation in the
outgassing, thereby demonstrating that the highest derived production
rates originate from the Wosret, Neith, and Bes regions during
perihelion.
Description:
The local H2O production rates of the comet
67P/Churyumov-Gerasimenko have been calculated from the lookup table
method described in the paper. This uses the spectra measured by MIRO
(Microwave Instrument for the Rosetta Orbiter) of the two water lines,
H2O16 and H2O18, to find an estimate for the local production
rate from the ratio between the two isotopologues. The measured
spectra are compared to results from a radiative transfer forward
model. Results are given from August 2014 to April 2016. For each
date, the following data are provided: the heliocentric distance of
the comet, the observed region as defined by El-Maary et al.
(2016A&A...593A.110E 2016A&A...593A.110E), the production rate (molec/s), and the error on
the measurement (molec/s).
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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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
miroq17.dat 79 3041 Production rate Q data from MIRO
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See also:
J/A+A/520/A92 : Comet 67P global plasma parameter simulation (Gortsas+ 2010)
J/A+A/527/A113 : 67P/Churyumov-Gerasimenko R-band light curve (Tubiana+ 2011)
J/A+A/548/A12 : 67P/Churyumov-Gerasimenko R-band light curve (Lowry+, 2012)
J/MNRAS/462/S138 : Robotic view of 67P perihelion (Snodgrass+, 2016)
J/A+A/600/A3 : Comet ion acoustic waves code (Gunell+, 2017)
Byte-by-byte Description of file: miroq17.dat
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Bytes Format Units Label Explanations
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1- 19 A19 "datime" Date Date and time of observation
(YYYY-MM-DDThh:mm:ss)
21- 33 F13.11 AU Rh Heliocentric distance of comet
35- 42 A8 --- Region Region defined by El-Maary et al.
(2016A&A...593A.110E 2016A&A...593A.110E)
44- 60 E17.12 s-1 Q Local production rate (in molecule/s)
62- 79 E18.13 s-1 e_Q Error on local production rate (in molecule/s)
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Acknowledgements:
David Marshall, marshall(at)mps.mpg.de
(End) Patricia Vannier [CDS] 24-Apr-2017