Dileep, Athul ; Joshi, Santosh ; Alexeeva, Sofya ; Kochukhov, Oleg ; Semenko, Eugene ; De Cat, Peter ; Zúñiga-Fernández, Sebastián ; Trust, Otto ; Pollard, Karen ; Crause, Lisa ; Barkaoui, Khalid ; Gillon, Michaël ; Jehin, Emmanuel ; Rathore, Neeraj

published in Monthly Notices of the Royal Astronomical Society, 542 issue 2, pp. 747--761 (2025)

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 T_eff = 11 850 K, logg = 4.57, υsini = 60 kms^{-1}, and an inclination angle i = 72 deg. 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 deg 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.

Keyword(s): Line: profiles ; Stars: abundances ; Stars: chemically peculiar ; Stars: individual: HD100357 ; Stars: rotation ; Stars: starspots ; Solar and Stellar Astrophysics
DOI: 10.1093/mnras/staf1247