Sarkar, Mrinmoy ; Semenko, Eugene ; Dupret, Marc-Antoine ; Trust, Otto ; De Cat, Peter ; Joshi, Santosh ; Lampens, Patricia ; Goswami, Aruna ; Mkrtichian, David ; Karinkuzhi, Drisya ; Yakunin, Ilya

submitted to Monthly Notices of the Royal Astronomical Society (2024)

Abstract: We present the results of a photometric analysis and asteroseismic modelling of a pulsating star HD 118660 (TIC 171729860). This work is based exclusively on the space-based TESS photometry, and it is the first part of broader efforts aimed at the in-depth description of individual objects surveyed under the “Nainital-Cape Survey” project. For a pulsating chemically peculiar Am star HD 118660, we have identified four radial (ℓ = 0) and five dipole (ℓ = 1) modes of photometric frequencies in short (2-mins) cadence TESS (sector 23) data. The asteroseismic large frequency separation, Δ𝜈, has been estimated as 4.31 d−1 , which constrained the stellar position in the post-MS phase of evolution. From 462 stellar models (with no overshoot) of different masses (within 𝛿 Scuti limit) and metallicity grids, based on the seismic-𝜒2 distribution test, we have obtained the best-fit parameters of mass, metallicity, and age as 1.46 ± 0.06 M⊙ , 0.006 ± 0.002, 1.672 ± 0.154 Gyr, respectively. The eigenfrequencies corresponding to the best-fit model give a good visual fit in an échelle diagram and follow the Petersen diagram. Later we tuned the models by considering a grid of overshooting parameters ranging from 0 to 0.5 fixing the other parameters at the zero overshoot minimum. This results in a better estimation of 𝜒2 for AlphaOver=0.3, which modifies the age estimation and poses the star in the post-MS phase. In the example of HD 118660, we have shown that diffusion and convective mixing play a significant role in chemically peculiar stars. The current study could significantly impact the theory explaining the excitation of pulsation modes in this category of stars.

Funding: BL/33/IN12 (BINA)