s-Process Enhancement and the Presence of Tc in 84 Carbon Stars

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Session 46 -- Late Type Stars
Display presentation, Wednesday, 9:20-6:30, Heller Lounge Room

[46.17] s-Process Enhancement and the Presence of Tc in 84 Carbon Stars

C. Barnbaum (UCB), M. Morris (UCLA)

The Third Dredge-up in Asymptotic Giant Branch stars enhances s- process elements in the atmosphere of these stars. $^{99}Tc$, an s- process element with a half-life on the order of the lifetime of an AGB star, is thereby expected to be present in oxygen- and carbon-rich AGB stars. However, Little et al. (1987) found 140 of 206 of oxygen-rich AGB stars to lack Tc. Furthermore, Smith \& Lambert (1988) found that 22 of 58 of S and MS stars without Tc are s-process enhanced. Smith \& Lambert and Brown et al. (1990) conclude that these S stars are likely to be mass transfer binaries, akin to the CH and Ba stars. To date, only 19 carbon stars have been observed for the presence of Tc. Clearly, a larger sample is needed to make adequate comparisons with the results for M and S stars. However, the relatively strong blue resonance lines of Tc are very difficult to observe in carbon stars, since carbon stars are extremely faint in this region (near 4300 \AA). We have determined that an easily observed intercombination line of Tc at 6085 \AA, although weak, traces the presence of Tc in carbon stars.

We present Tc and s-process detections in 84 carbon stars. We find that the ratio of Tc to Fe line depths is generally correlated with the carbon abundance and temperature classification of the carbon stars in our sample, as are the line depths of the light s-process elements Zr and Y. That 26\% of these carbon stars do not have Tc is consistent with the results for S stars. Of these 22 carbon stars lacking Tc, 6 stars do not have enhanced s-process elements and might not be on the AGB. The other 16 without Tc, yet having s-process enhancement, are candidates for mass transfer binaries.

This work was partially supported by NSF grant AST-9218157

Brown et al. 1990, AJ, 99, 1930 Little et al. 1987, AJ, 84, 1374 Smith \& Lambert 1988, ApJ, 333, 219

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