A DETACHED DUST SHELL SURROUNDING THE J-TYPE CARBON STAR Y CANUM VENATICORUM
This paper reports the first clear detection of a de- tached dust shell surrounding the prototypical J-type carbon star Y CVn in 90 m and 160 m maps taken with the ISO/ISOPHOT 1 . The projected inner radius of the shell is 180 -190 , corresponding to (6.4-7.1) 10 17 cm at a distance of 250 pc. The shell thickness is obtained to be (2-5) 10 17 cm. The mass-loss rate at the formation of the shell is estimated to be in the range (7-20) 10 6 M yr 1 , about two orders of magni- tude 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. It is concluded that the mass-loss rate decreased by two orders of magnitude on a short time scale 1.4 10 4 years ago as- suming an average shell expansion velocity of 15 km s 1 ,a nd 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 10 4 years even if the asymmetry in the shell geometry is taken into account. The evolutionary status of Y CVn is also discussed.
Abundance analysis of cool carbon stars
Curve-of-growth analyses for thirty cool carbon stars have been made, and physical parameters and relative abundances for fourteen elements have been determined. In J-type cool carbon stars, abundances of s-process elements with respect to Fe are nearly normal. In normal carbon stars of C5~C8, heavy metals are overabundant by factors of l0~100, and rare-earth elements are overabundant by a factor of about 10.
Finite Difference Modeling on the Temperature Field of Substrate in Friction Surfacing
Friction surfacing is an advanced process of great potential, especially in the field of repair and reclamation of worn and damaged components. As a kind of thermal processing technology, the temperature profile and changes of the substrate in friction surfacing are important factors to get coatings of high quality. In this paper, the temperature field of the substrate during the process is simulated by finite difference method. The results are consistent with experiments, reappearing the temperature change of the substrate during friction surfacing, allowing further study on figuration and quality of coatings.