Behavior of Abundances in Chemically Peculiar Dwarf and Subgiant A-Type Stars: HD 23193 and HD 170920*

Abstract

To understand the origin of the abundance peculiarities of non-magnetic A-type stars, we present the first detailed chemical abundance analysis of a metallic line star HD 23193 (A2m) and an A-type subgiant HD 170920 (A5) which could have been a HgMn star on the main sequence. Our analysis is based on medium (R∼14 000) and high (R∼40 000) resolution spectroscopic data of the stars. The abundance of 18 elements are derived: C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Sr, Y, and Ba. The masses of HD 23193 and HD 170920 are estimated from evolutionary tracks, as 2.3±0.1 M and 2.9±0.1 M . The ages are found 635±33 Myr for HD 23193 and 480±50 Myr for HD 170920 using isochrones. The abundance pattern of HD 23193 shows deviations from solar values in the iron-peak elements and indicates remarkable overabundances of Sr (1.16), Y (1.03), and Ba (1.24) with respect to the solar abundances. We compare the derived abundances of this moderately rotating (vsini = 37.5 km s −1 ) Am star to the theoretical chemical evolution models including rotational mixing. The theoretically predicted abundances resemble our derived abundance pattern, except for a few elements (Si and Cr). For HD 170920, we find nearly solar abundances, except for C (−0.43), S (0.16), Ti (0.15), Ni (0.16), Zn (0.41), Y (0.57), and Ba (0.97). Its low rotational velocity (vsini = 14.5 km s −1 ), reduced carbon abundance, and enhanced heavy element abundances suggest that the star is most-likely an evolved HgMn star.

Mass–effective temperature–surface gravity relation for intermediate-mass main-sequence stars

“…The typical uncertainty of 2.8% for T eff agrees well with those obtained from spectroscopic studies today (e.g., T eff = 7500 ± 200, 11 000 ± 300, 18 000 ± 500). However, the typical uncertainty of 0.02 dex for log g in binary star solutions is much more precise than the ∼0.05−0.20 dex uncertainties that can be achieved by spectroscopic methods (see, e.g., Fossati et al 2011;Gebran et al 2016;Kılıçoglu et al 2018). Recent chemical abundance studies with spectral data of different quality also indicate that the iron abundance [Fe/H] of stars can be derived with an uncertainty mostly in the range 0.08-0.20 dex.…”