HD 54361: evidence for the status of a low mass TP-AGB star

Abstract

The mass of the cool carbon star HD 54361 was suspected to be high, assuming the membership in the stellar association CMa OB1, in conflict with the theory of stellar evolution. The Gaia parallax and a high-resolution spectrum in the wavelength region from about 4800 to 6900 Å was employed in order to update the distance, atmospheric parameters and abundances using the method of spectral synthesis and new model atmospheres. Absorption lines are broad in the spectrum presumably because of a large macroturbulence, ξRT=10±1kms‑1. Radial-velocity monitoring revealed a scatter of about 4 km s^‑1, which reflects probably a large scale convection in the atmosphere. The effective temperature was found to be about 3200 K by modelling the wings of Na I D doublet, a somewhat higher than that estimated from the angular diameter. The difference in the temperature could be due to the light/colour variation. The abundances of iron peak elements calculated from less blended lines blueward of 5000 Å are near solar, [M/H]=0.0±0.2dex. The neutron-capture elements are enhanced up to 1 dex. The parallax leads to the distance of 554‑41+49pc, the absolute magnitude, MK=‑7.7±0.2mag, and the bolometric magnitude, Mbol(K)=‑4.6±0.2mag. The observed stellar parameters and abundances are typical values for the low mass ∼1.8M⊙ star on the TP-AGB branch according to the isochrone calculated for logAge(yr)=9.20 with solar initial metallicity. HD 54361 possibly belongs to the spike in the TP-AGB star numbers associated with the AGB-boosting effect.