Asteroseismology of the mild Am $\delta$ Sct star HD 118660 : TESS photometry and modelling

TL;DR

This study uses TESS photometry and seismic modelling to analyze the pulsations of the mild Am star HD 118660, revealing high-order radial modes and providing insights into its internal structure and stellar parameters.

Contribution

It presents the first detailed asteroseismic analysis of HD 118660, identifying pulsation modes and exploring stellar model parameters with seismic data.

Findings

Detected 15 and 16 pulsation frequencies in TESS sectors 23 and 50.

Identified radial and dipolar pulsation modes, including high-order overtones.

Radial mode analysis alone is insufficient to constrain overshooting and metallicity.

Abstract

We present the results of an asteroseismic study of HD 118660 (TIC 171729860), being a chemically peculiar (mild Am) star exhibiting $\delta$ Scuti ($\delta$ Sct) pulsations. It is based on the analysis of two sectors of time-series photometry from the space mission TESS and seismic modelling. It yielded the detection of 15 and 16 frequencies for TESS sectors 23 and 50, respectively. The identified pulsation modes include four radial ($\ell=0$) and five dipolar ($\ell=1$) ones. The radial modes are overtones with order $n$ ranging from $3$ and $6$. Such high values of $n$ are theoretically not expected for stars with the effective temperature of HD 118660 ($\rm T_{\rm eff}\approx 7550 \rm K$ ) located near the red edge of the $\delta$ Sct instability strip. To estimate the asteroseismic parameters, we have generated a grid of stellar models assuming a solar metallicity ($Z=0.014$) and different values for the convective overshooting parameter ($0.1\leq \alpha_{\rm ov}\leq 0.3$). We conclude that the analysis of the radial modes is insufficient to constrain $\alpha_{\rm ov}$ and $Z$ for $\delta$ Sct stars. The value for the equatorial velocity of HD 118660 derived from the seismic radius and the rotational frequency is consistent with values found in the literature.