Evolutionary status of the spectral variable BD + 48°1220 = IRAS 05040+4820

Abstract

Based on high-resolution observations (R = 60 000 and 75 000), we have studied the optical spectral variability of the star BD + 48°1220, identified with the IR source IRAS 05040+4820. We have measured the equivalent widths of numerous absorption lines of neutral atoms and ions at wavelengths from 4500 A to 6760 A, as well as the corresponding radial velocities. We use model atmospheres to determine the effective temperature T eff = 7900 K, surface gravity log g = 0.0, microturbulence velocity ξ t = 6.0, and the abundances for 16 elements. The star’s metallicity differs little from the solar value: [Fe/H] = −0.10 dex. The main peculiarity of the chemical composition of the star is a large helium excess, derived from the Hel λ 5876 A absorption, [He/H] = +1.04, and the equally large oxygen excess, [O/Fe] = +0.72 dex. The carbon excess is small, [C/Fe] = +0.09 dex, and the ratio [C/O] < 1. We obtained an altered relation for the light-metal abundances: [Na/Fe] = +0.87 dex with [Mg/Fe] = −0.31 dex. The barium abundance is low, [Ba/Fe] = −0.84 dex. It is concluded that the selective separation of elements onto dust grains of the envelope is probably efficient. The radial velocity of the star measured from photospheric absorption lines over three years of observations varies in the interval V ⊙ = −(7–15) km/s. Time-variable differential line shifts have been revealed. The entire set of available data (the luminosity M v ≈ −5 m , velocity V lsr ≈ −20 km/s, metallicity [Fe/H] = −0.10, and peculiarities of the optical spectrum and chemical composition) confirms the status of BD + 48°1220 as a post-AGB star with He and O excesses belonging to the Galactic disk.