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

TL;DR

This study provides the first detailed chemical abundance analysis of two A-type stars, HD 23193 and HD 170920, revealing peculiar abundance patterns and evolutionary statuses, and compares observations with theoretical models.

Contribution

It offers new detailed chemical abundance data for these stars and insights into their evolutionary states and peculiarities, especially regarding HgMn characteristics.

Findings

HD 23193 shows overabundances of Sr, Y, Ba.

HD 170920 has nearly solar abundances with some heavy element enhancements.

The observed abundances generally agree with theoretical models including rotational mixing.

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$\sim$14000) and high (R$\sim$40000) 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 $2.3\pm0.1$ $M_{\odot}$ and $2.9\pm0.1$ $M_{\odot}$. The ages are found $635\pm33$ Myr for HD 23193 and $480\pm50$ 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 ($v$sin$i = 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 ($v$sin$i = 14.5 $ km s$^{-1}$), reduced carbon abundance, and enhanced heavy element abundances suggest that the star is most-likely an evolved HgMn star.