1996A&A...315L.221I

This paper reports the first clear detection of a detached dust shell surrounding the prototypical J-type carbon star Y CVn in 90µm and 160µm maps taken with the ISO/ISOPHOT. The projected inner radius of the shell is 180"-190", corresponding to (6.4-7.1)x10¹⁷cm at a distance of 250pc. The shell thickness is obtained to be (2-5)x10¹⁷cm. The mass-loss rate at the formation of the shell is estimated to be in the range (7-20)x10^–6M_☉/yr, about two orders of magnitude higher than the present-day mass-loss rate derived from CO gas observations. The obtained mass in the shell is (4-14)x10^–2M_☉. It is concluded that the mass-loss rate decreased by two orders of magnitude on a short time scale 1.4x10⁴ years ago assuming an average shell expansion velocity of 15km/s, and that Y CVn has been staying at the low mass-loss state. The duration of the previous higher mass-loss phase would be at most 2x10⁴ years even if the asymmetry in the shell geometry is taken into account. The evolutionary status of Y CVn is also discussed.