Seungwon Lee^a et al. (>10)*
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^aJet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

We present sub-millimeter observations of the ground-state rotational transition (1₁₀–1₀₁) of water vapour from comet C/2002 T7 (LINEAR) obtained with the MIRO Instrument on the ESA Rosetta Spacecraft (s/c) Orbiter on April 30, 2004. At the time of the observations, the comet was at a distance of 0.63 AU from the Sun, 0.68 AU from the MIRO telescope, and about 7.5 days after its perihelion. The ground state rotation transition of ortho-water at 556.936 GHz was observed and integrated for ∼ 8 hours using a frequency switched radiometer to provide short and long term stability. The MIRO beam size is 7.5 arcmin in terms of full width half maximum, corresponding to a radius of 1.1×10⁵ km at the comet location. The observed signal line area of the water line spectrum is 4.3±0.8 K km/s. Using a molecular excitation and radiation transfer model and assuming the spherically symmetric and constant radial expansion of gas in the coma, we estimate that the production rate of water is (1.0±0.2)x10³⁰ molecules/s and the expansion velocity is 1.1±0.2 km/s at the time of the MIRO observation. The present estimation of the water outgassing rate of the comet is in good agreement with other observation-based estimations when the outgassing rates with respect to the time after perihelion are compared. The Doppler-correctd center velocity of the observed line was red-shifted by 0.67±0.13 km/s, of which only 0.18 km/s shift is explained by the model and attributed to a self-absorption effect. The potential sources of the additional red shift are discussed.

Reference
Lee et al. (in press) Sub-millimeter Observation of Water Vapor at 557 GHz in Comet C/2002 T7 (LINEAR). Icarus
[doi:10.1016/j.icarus.2014.05.004]
Copyright Elsevier

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