Chemical abundances and Doppler imaging of the Ap Si/He-wk star HD 100357

Abstract

We present the results of time-resolved photometry, abundance analysis, and Doppler imaging of an Ap star, HD 100357. The TESS photometry revealed rotational modulation with a period of 1.6279247 d. Upon inspecting the residuals after removing the rotational period and its harmonics, we found additional frequencies around 15.8054 d−1 , which we later confirmed with ground-based observations as originating from a nearby star. Using high-resolution spectroscopy, we identified HD 100357 as an Ap Si/He-wk star exhibiting rotational modulation caused by surface abundance spots. The stellar parameters of HD 100357 were determined as Teff = 11 850 K, log g = 4.57, υ sin i = 60 km s−1 , and an inclination angle i = 72◦. The detailed abundance analysis revealed strongly overabundant stratified silicon, an overabundance of iron-peak elements and rare earth elements combined with remarkably deficient helium. Mapping of Fe and Cr abundances revealed the existence of ring-shaped regions with a lower concentration of the elements. Their geometry might reflect the orientation of the hypothetical magnetic field of the star, oriented ∼ 90◦ to the rotational axis. HD 100357, with its strong chemical peculiarities and indications of possible magnetic fields, represents an interesting candidate for follow-up spectropolarimetric observations aimed at investigating its magnetic field topology and stellar activity.