Testing the presence of lithium on the surfaces of cool Ap stars

Abstract

Abstract. The possibility of a quite high Li abundance in the Ap stars was first raised by Wallerstein & Merchant (1965). Since then many studies investigated the problem of Li. The more recent observations in the lithium region indicate that in some Ap stars the λ6708 feature is variable and this variability can be explained by the existence of Li rich spots on the stellar surface. Atomic data for the Ce ii λ6708.099 were released by the D.R.E.A.M. database in 2002. The line was used to identify the prominent suspected Li-feature in post AGB stars and might as well be responsible for the absorption feature in Ap stars. Recent studies have mentioned this possibility, but it has yet to be investigated in more detail. Other physical phenomena, such as the occurrence of a partial Paschen-Back effect in the presence of magnetic fields, as well as possible hyperfine structure splitting of some Rare Earth transitions, must be taken into account to provide correct line identifications in the wavelength region around the Li-doublet at λ6708. We discuss a possible strategy to clarify the presence of Li in Ap stars.

The Paschen-Back effect in the Li I 6708 Å line and the presence of lithium in cool magnetic Ap stars

“…Mathys (1991) presented another theoretical calculation of the Paschen-Back splitting in the lithium line. Mathys (1990) and Nesvacil et al (2004) stressed the importance of taking this effect into account in the analyses of the Li feature in Ap stars. However, several recent studies of the Li i line in magnetic stars, even those supposedly presenting refined modelling of the Li transition in the magnetic fields exceeding 3-5 kG (e.g.…”