OGLE-GD-CEP-0516: The most metal-poor lithium-rich Galactic Cepheid

Abstract

Context. Classical Cepheids (DCEPs) are important astrophysical objects not only as standard candles for the determination of the cosmic distance ladder but also as a test-bed for stellar evolution theory thanks to the connection between their pulsation (periods, amplitudes) and stellar (luminosity, mass, effective temperature, metallicity) parameters. Aims. We aim to elucidate the nature of the Galactic DCEP OGLE-GD-CEP-0516 and other DCEPs showing an enhanced abundance of lithium in their atmospheres. Methods. We collected high-resolution spectra for OGLE-GD-CEP-0516 with UVES at VLT. Accurate stellar parameters, such as effective temperature, gravity, micro- and macro-turbulence, radial velocity, and metal abundances, were measured for this star using spectral synthesis techniques based on the LTE plane-parallel atmospheric model. Results. We find a chemical pattern, with most elements being under-abundant compared with the Sun; that is [Fe/H] = −0.54 ± 0.16 dex, [C/H] = −0.45 ± 0.05 dex, or [Mg/H] = −0.40 ± 0.16 dex, among others. In particular, we measured a lithium abundance of A(Li) = 3.06 ± 0.10 dex for OGLE-GD-CEP-0516, which makes this object the sixth Li-rich object to be identified among the Milky Way DCEPs. Conclusions. Our results favour the scenario in which the six Galactic Li-rich DCEPs are crossing the instability strip for the first time having had slowly rotating progenitors during their main sequence phase. This study explores the link between lithium abundance and the pulsation period in classical Cepheids. We find that brighter Cepheids, indicative of higher mass, show enhanced lithium abundance, contrary to predictions from evolutionary models considering rotation. Additionally, our analysis of lithium abundance versus [Fe/H] reveals a lack of significant correlation, contradicting expectations from galactic chemical evolution (GCE) models.