J/A+A/701/A61ivo://CDS.VizieR/J/A+A/701/A61doi:10.26093/cds/vizier/bc-nx/lgbCDSHmiddouch S.Jehin E.Lippi M.Vander Donckt M.Aravind K.,Hutsemekers D.Manfroid J.Jabiri A.Moulane Y.Benkhaldoun Z.2026-08-03T06:57:33Z2025-09-02T07:53:18ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frcometschemical-abundancesvisible-astronomyinfrared-astronomyBy 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, C_3_, and C_2_, using a Haser model as well as the dust proxy parameter A(0)f{rho}. 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 C_2_ probably originating from C_2_H_2_ rather than C_2_H_6_.2025A&A...701A..61Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/701/A61CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/701/A61https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/701/A61http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/701/A61https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/701/A61https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/701/A61http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/701/A61GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticalInfrareddefaultJ/A+A/701/A61/tablea2Gas production rates and A(0)f{rho} parameter of comet C/2017 K2 (PanSTARRS) from TRAPPIST datarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintDateUT Date'Y:M:D'time.epochnullablerhHeliocentric distanceaupos.distance;pos.heliocentricfloatrDeltaGeocentric distanceaupos.distance;pos.geocentricfloatOH? OH production rate (in molecules/s unit)s**-1phys.atmoldoublenullablee_OH? OH production rate error (in molecules/s unit)s**-1stat.errordoublenullableNH? NH production rate (in molecules/s unit)s**-1phys.atmoldoublenullablee_NH? NH production rate error (in molecules/s unit)s**-1stat.errordoublenullableCN? CN production rate (in molecules/s unit)s**-1phys.atmoldoublenullablee_CN? CN production rate error (in molecules/s unit)s**-1stat.errordoublenullableC2? C_2_ production rate (in molecules/s unit)s**-1phys.atmoldoublenullablee_C2? C_2_ production rate error (in molecules/s unit)s**-1stat.errordoublenullableC3? C_3_ production rate (in molecules/s unit)s**-1phys.atmoldoublenullablee_C3? C_3_ production rate error (in molecules/s unit)s**-1stat.errordoublenullableBC? Narrow-band BC at 445.3nm dust proxy parameter A(0)f{rho} (1)cmphys.atmoldoublenullablee_BC? Narrow-band BC at 445.3nm dust proxy parameter errorcmstat.errorfloatnullableRC? Narrow-band RC at 713.3nm dust proxy parameter A(0)f{rho} (1)cmphys.atmoldoublenullablee_RC? Narrow-band RC at 713.3nm dust proxy parameter errorcmstat.errorfloatnullableGC? Narrow-band GC at 525.9nm dust proxy parameter A(0)f{rho} (1)cmphys.atmoldoublenullablee_GC? Narrow-band GC at 525.9nm dust proxy parameter errorcmstat.errorfloatnullableRc? Broad-band dust continuum filter Rc filter dust proxy parameter A(0)f{rho} (1)phys.atmoldoublenullablee_Rc? Broad-band dust continuum filter Rc dust proxy parameter A(0)f{rho} errorstat.errorfloatnullable