TIC 308396022: a $\delta$ Scuti--$\gamma$ Doradus hybrid with large-amplitude radial fundamental mode and regular g-mode period spacing

TL;DR

This paper analyzes TIC 308396022, a hybrid star exhibiting both high-amplitude radial pulsations and regular gravity-mode period spacing, revealing insights into its binary nature and stellar evolution.

Contribution

It is the first detailed study of a $ ext{delta}$ Scuti--$ ext{gamma}$ Doradus hybrid with a high-amplitude radial mode and regular g-mode spacing, including evidence of a binary companion.

Findings

Radial fundamental mode identified at 13.2036 d$^{-1}$.

Regular g-mode period spacing of about 2460 s.

Evidence of a binary companion, likely a white dwarf.

Abstract

We analyse the pulsating behaviour of TIC 308396022 observed by the TESS mission. The star is a high-amplitude $\delta$ Sct star (HADS) that shows a very rich amplitude spectrum using the 3-yr light curve. Among these frequencies, the strongest peak of $f_{1}= 13.20362567(12) \rm{d^{-1}}$ is identified as the radial fundamental mode, and we also find the first and second overtones ($f_2$ and $f_3$). In the low frequency range (< 2.5 $\rm{d^{-1}}$), 22 peaks are identified to be gravity modes, which show a regular period spacing of about 2460\,s and have the angular degree $l = 1$. The period spacing pattern does not show a significant downward trend, suggesting the star rotates slowly. We note that this is a $\delta$ Sct--$\gamma$ Dor hybrid star containing a high-amplitude radial fundamental mode and a regular g-mode period spacing pattern. With O-C analysis, we find the star shows a significant time delay, implying that the star has a companion which is likely to be a white dwarf. The history of possible mass transfer provides a great opportunity to test the current theories of binary evolution, mass transfer, and pulsation.