A detached dust shell surrounding the J-type carbon star Y Canum Venaticorum

H. Izumiura - O. Hashimoto - K. Kawara - I. Yamamura - L. B. F. M. Waters

Abstract:

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 M_solar 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 M_solar. 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

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