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Session 97 - Planetary Nebulae.
Display session, Thursday, January 16
It has long been a mystery that \sim1% of K giants have Li enhancement, given that models for the red giant stage predict Li depletion due to mixing. The carbon isotope ratio is also a measure of the degree of internal mixing that has taken place in the star, so one would expect a correlation of ^12C/^13C with Li strength. However, da Silva et al.\ [1995, ApJ, 448, L41] have found no clear correlation of the carbon isotope ratio with Li abundance for five extreme Li-rich giants, yet these exceptional stars, as a group, have lower ^12C/^13C than normal K giants.
The central star in IRAS09371+1212 (the Frosty Leo Nebula) is a K 7 III giant, believed to be a post-asymptotic giant branch object. Our high resolution optical spectra show some unusual features: the resonance line of K I is an inverse P-Cygni profile, and Li is enhanced (W_eq=0.3 ÅOur millimeter observations of ^12CO(J=1--0) and ^13CO(J=1--0) yield a particularly low isotopic ratio (^12C/^13C), possibly as low as or lower than 2, giving Frosty the lowest value ever reported for K giants. We will discuss the relation of this object to others with large Li abundances and small carbon isotope ratios, such as the other Li-rich K giants and the J-type carbon stars.
Program listing for Thursday