Lithium in the symbiotic Mira V407 Cyg

Abstract

We report an identification of the lithium resonance doublet Li i 6708 Å in the spectrum of V407 Cyg, a symbiotic Mira with a pulsation period of about 745 d. The resolution of the spectra used was R=λ/Δλ≈ 18 500 and the measured equivalent width of the line is ∼0.34 Å. It is suggested that the lithium enrichment is due to hot bottom burning in the intermediate-mass asymptotic giant branch (AGB) variable, although other possible origins cannot be totally ruled out. In contrast to lithium-rich AGB stars in the Magellanic Clouds, ZrO λλ5551, 6474 absorption bands were not found in the spectrum of V407 Cyg. These are the bands used to classify the S-type stars at low-resolution. Although we identified weak ZrO λλ5718, 6412 these are not visible in the low-resolution spectra, and we therefore classify the Mira in V407 Cyg as an M type. This, together with other published work, suggests lithium enrichment can precede the third dredge up of s-process enriched material in galactic AGB stars.