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

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.

Two High-amplitude δ Scuti–γ Doradus Hybrids Constrained by the Radial Fundamental p and Equally Spaced g Modes

“…Recently, the first HADS star with regular-period-spaced g modes was discovered by Yang et al (2021) from TESS photometric data. Such a star is very interesting, since its δ Scuti-type oscillations may be easily recognized.…”

Uncorrelated Amplitude and Frequency Variations of the Harmonics in SX Phoenicis Star XX Cygni

“…High-amplitude δ Scuti stars (hereafter HADS) are a subclass of δ Scuti stars, who always have larger amplitudes and slower rotations. Most of the HADS show single or double radial pulsation modes (Niu et al 2013(Niu et al , 2017Xue et al 2018;Alton 2019;Bowman et al 2021;Daszyńska-Daszkiewicz et al 2022;Alton 2022a,b,c), and some of them have three radial pulsation modes (Handler et al 1998;Wils et al 2008;Mow et al 2016;Yang et al 2021;Kazarovets et al 2020;Khruslov 2014Khruslov , 2022Poleski et al 2010; or even some non-radial pulsation modes (Poretti et al 2011). SX Phoenicis (SX Phe) stars, a subgroup of HADS, are old Population II stars, which are characterized by high amplitudes of pulsation, low metallicity, and large spatial motion.…”

Uncorrelated Amplitude and Frequency Variations of the Harmonics in SX Phoenicis Star XX Cygni

“…High-amplitude δ-Scuti stars (hereafter HADS) are a subclass of δ-Scuti stars, which always have larger amplitudes and slower rotations. Most of the HADS show single or double radial-pulsation modes (Niu et al 2013(Niu et al , 2017Xue et al 2018;Alton 2019, Bowman et al 2021Alton 2022aAlton , 2022bDaszyńska-Daszkiewicz et al 2022), and some of them have three radial-pulsation modes (Handler et al 1998;Wils et al 2008;Mow et al 2016;Yang et al 2021, Poleski et al 2010Khruslov 2014;Kazarovets et al 2020;Khruslov 2022;, or even some nonradial pulsation modes (Poretti et al 2011) , V = 11.86 mag) is an Population II SX Phe star pulsating with a single radial mode (Ceraski 1904;Nijland 1923;McNamara & Feltz 1980;Szeidl & Mahdy 1981;Joner 1982;Hintz & Joner 1997;Kiss & Derekas 2000;Zhou et al 2002;Blake et al 2003), which shows a continuous linearperiod variation rate of (1/P 0 )( dP 0 / dt) = 1.19(13) × 10 −8 yr −1 (Yang et al 2012). Although XX Cyg has a clean periodogram (which consists of the fundamental frequency f 0 = 7.4148 c day −1 and its harmonics), the residuals in the O − C diagram have deviations of about 0.001-0.005 day, which is an order of magnitude larger than the uncertainties of the times of maximum light (TML; about 0.0001 day).…”