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

## TL;DR

This study combines photometry, spectroscopy, and Doppler imaging to analyze the chemical surface inhomogeneities and potential magnetic features of the Ap star HD 100357, revealing complex abundance patterns and rotational modulation.

## Contribution

It provides the first detailed abundance mapping and characterization of surface features of HD 100357, highlighting its chemical peculiarities and potential magnetic field geometry.

## Key findings

- Detected rotational modulation with a 1.628-day period.
- Mapped ring-shaped abundance regions of Fe and Cr.
- Identified strong silicon overabundance and helium deficiency.

## Abstract

We present the results of time-resolved photometry, abundance analysis and Doppler imaging of an Ap star, HD 100357. The {\it TESS} photometry revealed rotational modulation with a period of 1.6279247 days. 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 $T_{\rm eff}$ = 11,850 K, $\log g$ = 4.57, $\upsilon\sin i$ = 60 km\,s$^{-1}$, and an inclination angle $i$ = 72$^{\circ}$. 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 $\sim$90$^{\circ}$ 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.