Letter to the Editor

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

¹ INAF – Osservatorio Astrofisico di Catania, Via S.Sofia 78, 95123 Catania, Italy
e-mail: giovanni.catanzaro@inaf.it
² INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Naples, Italy
e-mail: vincenzo.ripepi@inaf.it
³ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
e-mail: m.salaris@ljmu.ac.uk
⁴ INAF – Osservatorio Astronomico di Abruzzo, Via M. Maggini, s/n, 64100 Teramo, Italy
⁵ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁶ Institut für Physik und Astronomie, Universität Potsdam, Haus 28, Karl-Liebknecht-Str. 24/25, 14476 Golm (Potsdam), Germany

Received: 4 January 2024
Accepted: 8 February 2024

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.