Lithium Cepheid V708 Car with an unusual chemical composition

¹ Astronomical Observatory, Odessa National University, Shevchenko Park, 65014 Odessa, Ukraine
e-mail: vkovtyukh@ukr.net; andrievskii@ukr.net
² Institut für Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
³ GEPI, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
⁴ Physics of stars department, Crimean Astrophysical Observatory, Nauchny 298409, Crimea
⁵ South African Astronomical Observatory, PO Box 9, 7935 Observatory, Cape Town, South Africa
⁶ Southern African Large Telescope Foundation, PO Box 9, 7935 Observatory, Cape Town, South Africa

Received: 27 November 2023
Accepted: 9 February 2024

Abstract

Aims. The purpose of this work is to spectroscopically analyse the classical Cepheid V708 Car. A preliminary check of the spectrum of V708 Car showed that this is a lithium-rich supergiant. We also found that V708 Car has an unusual chemical composition in that the abundances of various elements correlate with their condensation temperatures. We tried to find an explanation of this feature, which is unusual for classical Cepheids.

Methods. For the spectroscopic analysis, we used methods based on the assumption of local and non-local thermodynamic equilibrium.

Results. We determined the fundamental parameters of our program star V708 Car. This long-period Cepheid has a mass of about 12 M_⊙. We derived the abundances of 27 chemical elements in this star. They are clearly correlated with their condensation temperature: the higher the condensation temperature, the lower the abundance (there are exceptions for sodium and barium, however). We explain this peculiar chemical composition of the V708 Car atmosphere by the gas–dust separation in the envelope of this star. A similar mechanism leads to the observed peculiarities of the chemical composition of λ Boo, W Vir, and asymptotic giant branch stars.