Asteroseismology of the mild Am δ Sct star HD 118660: TESS photometry and modelling

Abstract

We present the results of an asteroseismic study of HD 118660 (TIC 171729860), being a chemically peculiar (mild Am) star exhibiting δ Scuti ( δ Sct) pulsations. It is based on the analysis of two sectors of time-series photometry from the space mission TESS ( Transiting Exoplanet Survey Satellite ) 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 ( ℓ = 0) and five dipolar ( ℓ = 1) ones. The radial modes are o vertones 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 ( T eff ≈ 7550 K) located near the red edge of the δ 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 ≤ αov ≤ 0 . 3). We conclude that the analysis of the radial modes is insufficient to constrain αov and Z for δ 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