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H. Izumiura - O. Hashimoto - K. Kawara - I. Yamamura - L. B. F. M. Waters
This paper reports the first clear detection of a detached dust shell surrounding the prototypical J-type carbon star Y CVn in 90 micron and 160 micron maps taken with the ISO/ISOPHOT. The projected inner radius of the shell is 180"-190", corresponding to (6.4-7.1)1017cm at a distance of 250 pc. The shell thickness is obtained to be (2-5)1017 cm. The mass-loss rate at the formation of the shell is estimated to be in the range (7-20) 10-6 Msolar yr-1, 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)10-2 Msolar. It is concluded that the mass-loss rate decreased by two orders of magnitude on a short time scale 1.4 104 years ago assuming an average shell expansion velocity of 15 km s-1, 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 2 104 years even if the asymmetry in the shell geometry is taken into account. The evolutionary status of Y CVn is also discussed.
Keywords:
Stars: carbon - Stars: evolution - Stars: imaging -
Stars: individual: Y CVn - Stars: mass-loss - Stars: AGB and post-AGB - Dust