Evolutionary Status of the Ap Stars HD 110066 and HD 153882
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utionary Status of the Ap Stars HD 110066 and HD 153882 A. M. Romanovskaya1* , T. A. Ryabchikova1, and D. V. Shulyak2 1
Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya ul. 48, Moscow, 109017 Russia 2 Max-Planck Institut fur ¨ Sonnensystemforschung, Gottingen, ¨ Germany Received April 19, 2020; revised April 19, 2020; accepted April 28, 2020
Abstract—We present the results of our determination of the fundamental atmospheric parameters for the magnetic chemically peculiar Ap stars HD 110066 (AX CVn) and HD 153882 (V451 Her). The determination of the atmospheric parameters (Teff , log g, R/R , and L/L ) is based on a self-consistent analysis of high-resolution spectra (ESPaDOnS with R = 65 000) and the observed flux distribution in a wide spectral range. We have derived the radial magnetic field components Br = 4015 ± 180 G for HD 110066 and Br = 3800 ± 200 G for HD 153882 from the observed line splitting and magnetic differential broadening. We have analyzed the chemical composition and the vertical distribution (stratification) of Fe and Cr in atmospheric depth, because the lines of these elements make the greatest contribution to the absorption and stratification affects the distribution of the outgoing flux. We have constructed model atmospheres and determined the evolutionary status of these stars by taking into account the anomalous chemical composition and stratification. The positions of HD 110066 and HD 153882 on the Hertzsprung–Russell diagram confirm the observed decrease in the magnetic field strength with stellar age for stars with masses greater than 2.5 M . DOI: 10.1134/S1063773720050060 Keywords: magnetic stars, stellar atmospheres, spectroscopy.
INTRODUCTION Determining the fundamental parameters of stars (effective temperature Teff , surface gravity log g, radius R/R , and luminosity L/L ) is one of the main problems in astrophysics, because they determine the position of a star on the Hertzsprung–Russell (H–R) diagram, i.e., its evolutionary status and, consequently, age. This problem is very important for the theory of the formation and subsequent evolution of the magnetic fields of Ap stars and chemical anomalies. The evolution of the magnetic field and chemical anomalies over the lifetime of a star on the main sequence (MS) still remains uncertain mainly because of the difficulties in determining the age and/or position of an Ap star on the MS. Kochukhov and Bagnulo (2006) carried out a statistical analysis of the evolutionary status of 194 magnetic Ap stars and concluded that the surface-averaged magnetic field strength decreases with stellar age. The effective temperatures and luminosities were estimated from calibrations of narrow-band photometry and known parallaxes. Landstreet et al. (2007) studied the evolution of the magnetic fields of Ap stars based on *
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81 objects in open clusters of known age whose membership in the cluster was established with sufficient confidence. Based on this study, they reached the preliminary conclusion that the magnetic field decrease
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