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

• Published in: The Astrophysical journal 2018-01, Vol.852 (2), p.116
• Main Authors: Kılıçoğlu, Tolgahan, Çalışkan, Şeyma, Ünal, Kübraözge
• Format: Article
• Language: English
• Subjects: A stars; Abundance; Aluminum; Astrophysics; Barium; Chemical evolution; Chromium; Heavy elements; Iron; Magnesium; Manganese; Nickel; Organic chemistry; Peculiar stars; Rotation; Silicon; Stellar evolution; Strontium; Titanium; Yttrium; Zinc
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aa9f14

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 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 ⊙ and 2.9 ± 0.1  M ⊙ . 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 ( 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 ( km s −1 ), reduced carbon abundance, and enhanced heavy element abundances suggest that the star is most likely an evolved HgMn star.