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

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 similar to 14,000) and high (R similar to 40,000) resolution spectroscopic data of the stars. The abundances 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-circle dot and 2.9 +/- 0.1. M-circle dot. The ages are found to be 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 (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.