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Catalogue POP – Notice individuelle de publication

Cordiner M. A., Biver Nicolas, Crovisier Jacques, Bockelée-Morvan Dominique, Mumma Michael J., Charnley Steven B., Villanueva Gerónimo L., Paganini Lucas, Lis Darek C., Milam Stefanie N., Remijan Anthony J., Coulson I. M., Kuan Yi-Jehng, Boissier Jérémie

Thermal Physics of the Inner Coma: ALMA Studies of the Methanol Distribution and Excitation in Comet C/2012 K1 (PanSTARRS)

The Astrophysical Journal, 2017, vol. 837

Référence DOI : 10.3847/1538-4357/aa6211
Référence ADS : 2017ApJ...837..177C

Résumé :

We present spatially and spectrally resolved observations of CH<SUB>3</SUB>OH emission from comet C/2012 K1 (PanSTARRS), using the Atacama Large Millimeter/submillimeter Array on 2014 June 28--29. Two-dimensional maps of the line-of-sight average rotational temperature (T <SUB>rot</SUB>) were derived, covering spatial scales 0."3--1."8 (corresponding to sky-projected distances rho ~ 500--2500 km). The CH<SUB>3</SUB>OH column density distributions are consistent with isotropic, uniform outflow from the nucleus, with no evidence for extended sources of CH<SUB>3</SUB>OH in the coma. The {T}<SUB>{rot</SUB>}(rho ) radial profiles show a significant drop within a few thousand kilometers of the nucleus, falling from about 60 to 20 K between rho =0 and 2500 km on June 28, whereas on June 29, T <SUB>rot</SUB> fell from about 120 to 40 K between rho = 0 km and 1000 km. The observed T <SUB>rot</SUB> behavior is interpreted primarily as a result of variations in the coma kinetic temperature due to adiabatic cooling of the outflowing gas, as well as radiative cooling of the CH<SUB>3</SUB>OH rotational levels. Our excitation model shows that radiative cooling is more important for the J=7-6 transitions (at 338 GHz) than for the K=3-2 transitions (at 252 GHz), resulting in a strongly sub-thermal distribution of levels in the J=7-6 band at rho &gsim; 1000 {km}. For both bands, the observed temperature drop with distance is less steep than predicted by standard coma theoretical models, which suggests the presence of a significant source of heating in addition to the photolytic heat sources usually considered.

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