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Astron. Astrophys. 315, L221-L224 (1996)

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

H. Izumiura1, O. Hashimoto2, K. Kawara3,4, I. Yamamura5,6, and L.B.F.M. Waters7,6

1 Okayama Astrophysical Observatory, National Astronomical Observatory, Kamogata, Asakuchi, Okayama 719-02, Japan
2 Department of Applied Physics, Seikei University, 3 Kichijojikita, Musashino, Tokyo 180, Japan
3 Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229, Japan
4 ISO Science Operations Centre, Astrophysics Division of ESA, Villafranca, E-28080 Madrid, Spain
5 Institute of Astronomy, Faculty of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181, Japan
6 SRON Laboratory for Space Research Groningen, P.O. Box 800, 9700 AV Groningen, The Netherlands
7 Astronomical Institute, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

Received 18 July 1996 / Accepted 22 August 1996

Abstract. This paper reports the first clear detection of a detached dust shell surrounding the prototypical J-type carbon star Y CVn in 90 img1.gifm and 160 img1.gifm maps taken with the ISO/ISOPHOT*. The projected inner radius of the shell is 180''-190'', corresponding to (6.4-7.1)1017 cm 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 Mimg5.gif 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 Mimg5.gif . 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.

Key words: stars: carbon - stars: evolution - stars: imaging - stars: individual: Y CVn - stars: mass-loss - stars: AGB and post-AGB - dust

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA

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