# Unveiling the Variability and Chemical Composition of AL Col

## TL;DR

This study characterizes AL Col as a chemically peculiar star with rotational variability, detailed chemical abundances, and evidence of differential rotation, providing insights into its evolutionary status and magnetic properties.

## Contribution

It offers a comprehensive analysis combining photometry, spectroscopy, and modeling to reveal AL Col's chemical peculiarities, rotation, and evolutionary stage, which was not previously detailed.

## Key findings

- Rotational frequency of 0.09655 d^{-1} identified from TESS data.
- Star exhibits over-abundances of rare earth elements, classifying it as Ap/Bp-type.
- Evidence of differential rotation from spot modeling.

## Abstract

Using \tess\ short-cadence (120\,s) SAP flux, we identified a rotational frequency of 0.09655\,$\mathrm{d}^{-1}$ ($P_\mathrm{rot}=10.35733$\,d). Wavelet analysis reveals that while the amplitudes of the harmonic components vary over time, the strength of the primary rotational frequency remains stable. A SED analysis of multi-band photometric data yields an effective temperature ($T_\mathrm{eff}$) of {11,750\,K.} %MDPI: Comma added for five digits in the whole text, please check. High-resolution spectroscopic observations covering wavelengthrange 4500--7000\,\AA\ provide refined estimates of \teff\, =\, 13,814\, $\pm$\, 400\,K, \logg\,=\, 4.09\, $\pm$\, 0.08\,dex, and \vsini\, =\, 16 $\pm$ 1\,\kms. Abundance analysis shows solar-like composition of O\,\textsc{ii}, Mg\,\textsc{ii}, S\,\textsc{ii}, and Ca\,\textsc{ii}, while helium is under-abundant by 0.62\,dex. Rare earth elements (REEs) exhibit over-abundances of up to 5.2\,dex, classifying the star as an Ap/Bp-type star. AL\,Col has a radius of $R = 3.74\,\pm\,0.48{\rm R_{\odot}}$, with its H--R diagram position estimating a mass of $M = 4.2\,\pm\,0.2{\rm M_{\odot}}$ and an age of $0.12\,\pm\,0.01$ Gyr, indicating that the star has slightly evolved from the main sequence. The \tess\ light curves were modeled using a three-evolving-spot configuration, suggesting the presence of differential rotation. This star is a promising candidate for future investigations of magnetic field diagnostics and the vertical stratification of chemical elements in its atmosphere.

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Source: https://tomesphere.com/paper/2508.20681