We have used the unique far-UV imaging capability offered by a sounding rocket borne instrument to acquire observations of C/2012 S1 (ISON) when its angular separation with respect to the sun was 26.3deg, on 2013 November 20.49. At the time of observation the comet's heliocentric distance and velocity relative to the sun were rh = 0.43 AU and rh_dot = -62.7 km s^-1. Images dominated by C I 1657 A and H I 1216 A were acquired over a 1e6 x 1e6 km^2 region. The water production rate implied by the Lyman alpha observations is constrained to be Q_H2O approximately 8e29 s^-1 while the neutral carbon production rate was Q_C approximately 4e28 s^-1. The radial profile of C I was consistent with it being a dissociation product of a parent molecule with a lifetime approximately 5e4 seconds, favoring a parent other than CO. We constrain the Q_CO production rate to 5(+1.5, -7.5)e28 s^-1 with 1sigma errors derived from photon statistics. The upper limit on the Q_CO/Q_H2O < 6%.
@article{arxiv.1606.05873,
title = {Far-ultraviolet Observations of Comet C/2012 S1 (ISON) from FORTIS},
author = {Stephan R. McCandliss and Paul D. Feldman and Harold Weaver and Brian Fleming and Keith Redwine and Mary J. Li and Alexander Kutyrev and S. Harvey Moseley},
journal= {arXiv preprint arXiv:1606.05873},
year = {2016}
}
Comments
11 pages, 10 figures, Accepted for publication in AJ, 2016-June-17