HIFI observations of water in the atmosphere of comet C/2008 Q3 (Garradd)

Abstract

High-resolution far-infrared and sub-millimetre spectroscopy of water lines is an important tool to understand the physical and chemical properties of cometary atmospheres. We present observations of several rotational ortho-and para-water transitions in comet C/2008 Q3 (Garradd) performed with HIFI on Herschel. These observations have provided the first detection of the 2 12 −1 01 (1669 GHz) ortho and 1 11 −0 00 (1113 GHz) para transitions of water in a cometary spectrum. In addition, the ground-state transition 1 10 −1 01 at 557 GHz is detected and mapped. By detecting several water lines quasi-simultaneously and mapping their emission we can constrain the excitation parameters in the coma. Synthetic line profiles are computed using excitation models which include excitation by collisions, solar infrared radiation, and radiation trapping. We obtain the gas kinetic temperature, constrain the electron density profile, and estimate the coma expansion velocity by analyzing the map and line shapes. We derive water production rates of 1.7−2.8 × 10 28 s −1 over the range r h = 1.83−1.85 AU.

Ammonia and other parent molecules in comet 10P/Tempel 2 fromHerschel/HIFI and ground-based radio observations

“…This value best explains the brightness distribution of the 557 GHz line observed on 19 July (Szutowicz et al 2011 and in prep. ) and is consistent with values found in other comets Hartogh et al 2010). The model reproduces both the line intensity and the Doppler shift of the water line if we set Q H 2 O to 2.2 × 10 28 mol s −1 (Table 1).…”

A HERSCHEL STUDY OF D/H IN WATER IN THE JUPITER-FAMILY COMET 45P/HONDA-MRKOS-PAJDUŠÁKOVÁ AND PROSPECTS FOR D/H MEASUREMENTS WITH CCAT

“…To convert the observed line intensities into production rates (Table 1), we used an excitation model similar to that of Hartogh et al (2010, and Bockelée-Morvan et al (2012). Collisions with electrons use an electron density factor x ne = 0.2.…”

Herschel/SPIRE observations of water production rates and ortho-to-para ratios in comets

“…At the nucleocentric distances observed a constant T kin = 40 K is assumed as previous work has shown this value to be a good approximation (Combi et al 1999). Observations of the 110 − 101 (557 GHz) water line in other comets have constrained xn e to 0.2 (Biver 1997;Biver et al 2007;Hartogh et al 2010). Previous observations of 1P/Halley have shown that xr e , a scaling factor that determines the boundary radius between collisional excitation predominantly caused by water-water and water-electron, is equal to unity (Balsiger 1990;Festou 1990).…”

“…Adopted values for the other model parameters mentioned above are given in Table 1. Although this model makes some simplistic assumptions such as spherical symmetry of the outgassing, and in the irradiation and photochemistry of the water, the omission of vibrationally excited levels, and radiative transfer at infrared wavelengths a number of comet observations have been modeled with considerable success (Zakharov et al 2007;Hartogh et al 2010;Bockelée-Morvan et al 2012).…”