The high spectral resolution and sensitivity of Herschel/HIFI allows for the detection of multiple rotational water lines and accurate determinations of water production rates in comets. In this letter we present HIFI observations of the fundamental 110-101 (557 GHz) ortho and 111-000 (1113 GHz) para rotational transitions of water in comet 81P/Wild 2 acquired in February 2010. We mapped the extent of the water line emission with five point scans. Line profiles are computed using excitation models which include excitation by collisions with electrons and neutrals and solar infrared radiation. We derive a mean water production rate of 1.0×1028 molecules s−1 at a heliocentric distance of 1.61 AU about 20 days before perihelion, in agreement with production rates measured from the ground using observations of the 18-cm OH lines. Furthermore, we constrain the electron density profile and gas kinetic temperature, and estimate the coma expansion velocity by fitting the water line shapes.
@article{arxiv.1007.0149,
title = {Water production in comet 81P/Wild 2 as determined by Herschel/HIFI},
author = {M. de Val-Borro and P. Hartogh and J. Crovisier and D. Bockelée-Morvan and N. Biver and D. C. Lis and R. Moreno and C. Jarchow and M. Rengel and S. Szutowicz and M. Banaszkiewicz and F. Bensch and M. I. Błęcka and M. Emprechtinger and T. Encrenaz and E. Jehin and M. Küppers and L. -M. Lara and E. Lellouch and B. M. Swinyard and B. Vandenbussche and E. A. Bergin and G. A. Blake and J. A. D. L. Blommaert and J. Cernicharo and L. Decin and P. Encrenaz and T. de Graauw and D. Hutsemékers and M. Kidger and J. Manfroid and A. S. Medvedev and D. A. Naylor and R. Schieder and D. Stam and N. Thomas and C. Waelkens and R. Szczerba and P. Saraceno and A. M. Di Giorgio and S. Philipp and T. Klein and V. Ossenkopf and P. Zaal and R. Shipman},
journal= {arXiv preprint arXiv:1007.0149},
year = {2010}
}
Comments
Accepted for publication in A&A (special issue on HIFI first results)