TIC 308396022: δ Scuti–γ Doradus hybrid with large-amplitude radial fundamental mode and regular g-mode period spacing

¹ Ministry of Education Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, School of Physics, Xi’an Jiaotong University, 710049 Xi’an, PR China
e-mail: zuozyu@xjtu.edu.cn
² IRAP, Université de Toulouse, CNRS, CNES, UPS, Toulouse, France
³ Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, Camperdown, NSW 2006, Australia
⁴ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
⁵ Space Telescope Science Institute in Baltimore, Baltimore, MD, USA

Received: 10 September 2021
Accepted: 30 September 2021

Abstract

We analyse the pulsating behaviour of TIC 308396022, based on observations by the TESS mission. The star is a high-amplitude δ Sct star that shows a very rich amplitude spectrum using the 3-yr light curve. Among these frequencies, the strongest peak of f₁ = 13.20362567(12) d⁻¹ is identified as the radial fundamental mode, and we also find the first and second overtones (f₂ and f₃). In the low-frequency range (< 2.5 d⁻¹), 22 peaks are identified as gravity modes, which show a regular period spacing of about 2460 s and have an angular degree of l = 1. The period spacing pattern does not show a significant downward trend, suggesting the star is rotating slowly. We note that this is a δ Sct–γ Dor hybrid star containing a high-amplitude radial fundamental mode and a regular g-mode period spacing pattern. With the O − C analysis, we find the star shows a significant time delay, implying that the star has a companion and it is likely to be a white dwarf. The history of possible mass transfer provides a great opportunity for testing the current theories of binary evolution, mass transfer, and pulsation.