2005PASP..117.1182K

We report on the discovery of two lithium Cepheids in the Galaxy, based on observations made with the echelle spectrograph of the Apache Point Observatory. We have used high-resolution, high signal-to-noise ratio spectra to determine abundances of chemical elements in 16 classical Cepheids. Only two of our program stars show a lithium line, RX Aur and YZ Aur (RX Aur has been also classified by us as a new nonradial pulsator). For the others, including the stars with [N/C]<0.2, Li is depleted up to logN(Li)<1.0. Hence, it appears that mixing depletes Li before stars enter the instability strip. According to stellar models, the main mixing event takes place when T_effdrops below 4000 K, which is outside the red edge of the instability strip; i.e., after stars have crossed the instability strip for the first time.