Multi-element abundance Doppler imaging of the rapidly oscillating Ap star HR 3831

Abstract

Abstract. We investigate magnetic field geometry and surface distribution of chemical elements in the rapidly oscillating Ap star HR 3831. Results of the model atmosphere analysis of the spectra of this star are combined with the Hipparcos parallax and evolutionary models to obtain new accurate estimates of the fundamental stellar parameters: T eff = 7650 K, log L/L = 1.09, M/M = 1.77 and an inclination angle i = 68• of the stellar axis of rotation. We find that the variation of the longitudinal magnetic field of HR 3831 and the results of our analysis of the magnetic intensification of Fe  lines in the spectrum of this star are consistent with a dipolar magnetic topology with a magnetic obliquity β = 87• and a polar strength B p = 2.5 kG. We apply a multi-element abundance Doppler imaging inversion code for the analysis of the spectrum variability of HR 3831, and recover surface distributions of 17 chemical elements, including Li, C, O, Na, Mg, Si, Ca, Ti, Cr, Mn, Fe, Co, Ba, Y, Pr, Nd, Eu. Our study represents the most thorough examination of the surface chemical structure in a magnetic Ap star and provides important observational constraints for modelling radiative diffusion in magnetic stars. The exceedingly high quality of some of our spectroscopic data allowed us to reconstruct unprecedented details of abundance distributions, demonstrating a high level of complexity in the surface structure down to the resolution limit of the Doppler maps. The Doppler imaging analysis of HR 3831 forms a basis for subsequent detailed observational investigations and theoretical modelling of non-radial oscillations in this star. We discuss the compound effect of the chemical nonuniformities and pulsational velocity field on the rapid line profile variations, and assess the possibility of identifying pulsation modes by using spatial filtering produced by an inhomogeneous abundance distribution. The results of our study of the surface chemical structure suggest that differences in pulsational behaviour of lines of different ions observed for HR 3831 are not a consequence of horizontal atmospheric inhomogeneities, but predominantly a depth effect.

Multi-element Doppler imaging of the CP2 star HD 3980

“…Further information on the final linelist used for reconstructing abundance maps is given in the Table 2. The observed line profiles were inverted with the invers12 code (Kochukhov et al 2004). The code uses a regularized minimization algorithm and can treat many individual lines and their blends simultaneously.…”

“…The code uses a regularized minimization algorithm and can treat many individual lines and their blends simultaneously. A detailed description of the software and some practical applications are given by, e.g., Piskunov & Rice (1993), Lüftinger et al (2010), and Kochukhov et al (2004).…”

Pulsation of magnetic stars

“…Surface magnetic field moduli of some roAp stars are plotted with respect to the dominant oscillation frequencies. The magnetic field strengths were taken from Shulyak et al (2013), Ryabchikova et al (2008), Mathys et al (1997), Hubrig et al (2005), Kochukhov et al (2004), Balona et al (2013).…”

The fundamental parameters of the roAp star 10 Aquilae

“…Vertical and horizontal microscopic diffusion of the chemical elements (Michaud 1970) is thus believed to occur, leading to spotted surfaces that have been reconstructed by Doppler or ZeemanDoppler imaging for several (ro)Ap stars (Lüftinger et al 2003(Lüftinger et al , 2010Kochukhov et al 2004;Kochukhov & Wade 2010). Such abnormal surface layers might generate systematic errors when Article published by EDP Sciences A21, page 1 of 8 A&A 559, A21 (2013) determining stellar luminosities and effective temperatures by spectrometric or photometric techniques (Matthews et al 1999).…”