J/A+A/701/A61 Comet C/2017 K2 gas production rates (Hmiddouch+, 2025)
Variations in volatile-driven activity of comet C/2017 K2 (PanSTARRS) revealed
by long-term multi-wavelength observations.
Hmiddouch S., Jehin E., Lippi M., Vander Donckt M., Aravind K.,
Hutsemekers D., Manfroid J., Jabiri A., Moulane Y., Benkhaldoun Z.
<Astron. Astrophys. 701, A61 (2025)>
=2025A&A...701A..61H 2025A&A...701A..61H (SIMBAD/NED BibCode)
ADC_Keywords: Comets ; Abundances ; Optical ; Infrared
Keywords: comets: general - comets: individual: C/2017 K2 (PanSTARRS)
Abstract:
By conducting a comprehensive study of comets across a broad range of
heliocentric distances, we can improve our understanding of the
physical mechanisms that trigger their activity at various distances
from the Sun. At the same time, we can identify possible differences
in the composition of these outer solar system bodies belonging to
various dynamical groups. C/2017 K2 (PANSTARRS) is a Dynamically New
Oort Cloud comet (DNC) that has exhibited activity at an extremely
large heliocentric distance of 23.75au, was found to have a CO-rich
coma at 6.72au, and attracted the interest of the community to become
a bright DNC at perihelion.
We aim to study through photometry and spectroscopy the activity
evolution and chemical composition of C/2017 K2 over a long-term
monitoring from October 2017 (rh=15.18au) pre-perihelion to April
2025 (rh=8.46au) post-perihelion.
We used both TRAPPIST telescopes to monitor the activity with
broad-band and cometary narrow-band filters. We produced an 8-year
light curve and colors from the broad-band images and computed the
activity slopes. We derived the production rates of the daughter
species, OH, NH, CN, C3, and C2, using a Haser model as well as the
dust proxy parameter A(0)fρ. We used CRIRES+, the high-resolution
infrared echelle spectrometer of the ESO VLT, and UVES, its
high-resolution ultraviolet-visual echelle spectrograph, to study
simultaneously the parent and daughter species, at three different
epochs from May to September 2022, when the comet crossed the water
sublimation region.
C/2017 K2 (PanSTARRS) light curve shows a complex evolution of its
brightness, with several slopes and a plateau around perihelion,
revealing the onset and competition of various species. The
photometric analysis shows constant coma colors across the whole
heliocentric range, indicating similar properties of the dust grains
released during the survey, and in agreement with the colors of other
active long-period comets. The production rates indicate a typical
C2/CN composition and a high dust-to-gas ratio. The analysis of the
oxygen forbidden lines shows the transition between CO and CO2
dominating the comet's activity to the onset of the water
sublimation below 3.0au. Molecular abundance analysis from the IR
spectra classified C/2017 K2 as a typical-to-enriched comet, with HCN
identified as the main parent molecule of CN, and C2 probably
originating from C2H2 rather than C2H6.
Description:
Production rates of several volatile species (OH, NH, C3 , CN, and C2)
in comet C/2017 K2 and dust proxy parameter Afρ, measured using
the broad-band dust continuum filter (Rc), and the narrow-band dust
continuum filters (RC, GC, BC).
Orbital Elements:
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Comet i Tj Teri Tp rh-range
(deg) (au) (UTC) Pre/Post (au)
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C/2017 K2 (PanSTARRS) 87.55 0.17 1.79 19.12.2022 15.18-1.79-8.46
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Dates (Start/End): 25.10.2017-20.04.2025
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea2.dat 177 219 Gas production rates and A(0)fρ parameter of
comet C/2017 K2 (PanSTARRS) from TRAPPIST data
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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- 10 A10 "date" Date UT Date
13- 17 F5.2 au rh Heliocentric distance
19- 23 F5.2 au rDelta Geocentric distance
25- 32 E8.3 s-1 OH ? OH production rate (in molecules/s unit)
34- 41 E8.3 s-1 e_OH ? OH production rate error
(in molecules/s unit)
43- 50 E8.3 s-1 NH ? NH production rate (in molecules/s unit)
52- 59 E8.3 s-1 e_NH ? NH production rate error
(in molecules/s unit)
61- 68 E8.3 s-1 CN ? CN production rate (in molecules/s unit)
70- 77 E8.3 s-1 e_CN ? CN production rate error
(in molecules/s unit)
79- 86 E8.3 s-1 C2 ? C2 production rate (in molecules/s unit)
88- 95 E8.3 s-1 e_C2 ? C2 production rate error
(in molecules/s unit)
97-104 E8.3 s-1 C3 ? C3 production rate (in molecules/s unit)
106-113 E8.3 s-1 e_C3 ? C3 production rate error
(in molecules/s unit)
115-122 F8.2 cm BC ? Narrow-band BC at 445.3nm dust proxy
parameter A(0)fρ (1)
124-129 F6.2 cm e_BC ? Narrow-band BC at 445.3nm dust proxy
parameter error
131-138 F8.2 cm RC ? Narrow-band RC at 713.3nm dust proxy
parameter A(0)fρ (1)
140-145 F6.2 cm e_RC ? Narrow-band RC at 713.3nm dust proxy
parameter error
147-154 F8.2 cm GC ? Narrow-band GC at 525.9nm dust proxy
parameter A(0)fρ (1)
156-161 F6.2 cm e_GC ? Narrow-band GC at 525.9nm dust proxy
parameter error
163-170 F8.2 --- Rc ? Broad-band dust continuum filter Rc filter
dust proxy parameter A(0)fρ (1)
172-177 F6.2 --- e_Rc ? Broad-band dust continuum filter Rc
dust proxy parameter A(0)fρ error
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Note (1): The A(0)fρ values are computed within a radius aperture of
5-arcsecond from the nucleus and corrected for the phase angle effect.
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Acknowledgements:
Said Hmiddouch, shmiddouch(at)uliege.be
(End) Patricia Vannier [CDS] 22-Jul-2025