We report the preliminary results of a survey for water vapor in a sample of
eight C stars with large mid-IR continuum fluxes: V384 Per, CIT 6, V Hya, Y
CVn, IRAS 15194-5115, V Cyg, S Cep, and IRC+40540. This survey, performed using
the HIFI instrument on board the Herschel Space Observatory, entailed
observations of the lowest transitions of both ortho- and para-water: the
556.936 GHz 1(10)-1(01) and 1113.343 GHz 1(11)-0(00) transitions, respectively.
Water vapor was unequivocally detected in all eight of the target stars. Prior
to this survey, IRC+10216 was the only carbon-rich AGB star from which thermal
water emissions had been discovered, in that case with the use of the
Submillimeter Wave Astronomy Satellite (SWAS). Our results indicate that
IRC+10216 is not unusual, except insofar as its proximity to Earth leads to a
large line flux that was detectable with SWAS. The water spectral line widths
are typically similar to those of CO rotational lines, arguing against the
vaporization of a Kuiper belt analog (Ford & Neufeld 2001) being the general
explanation for water vapor in carbon-rich AGB stars. There is no apparent
correlation between the ratio of the integrated water line fluxes to the 6.3
micron continuum flux - a ratio which measures the water outflow rate - and the
total mass-loss rate for the stars in our sample.Comment: Accepted for publication in the Astrophysical Journal Letter