Pulsation Mode Identification and Classification of 46 High-Amplitude $\delta$ Scuti Stars from 50 Candidates with TESS observations

TL;DR

This study confirms 46 high-amplitude δ Scuti stars using TESS data, identifies their pulsation modes, refines the period-luminosity relation, and broadens understanding of their distribution in the HR diagram.

Contribution

It provides the first detailed pulsation mode identification for 40 HADS stars, refines the PL relation, and expands the known HR distribution of these variables.

Findings

46 confirmed HADS stars with detailed pulsation modes

Revised period-luminosity relation: M_V = -3.31 log P - 1.68

HADS stars are distributed beyond the narrow instability strip

Abstract

Asteroseismic modelling of high-amplitude $\delta$ Scuti (HADS) variables critically depends on their accurate classification, which provides robust constraints on stellar physical parameters. As a foundational step in this direction, we present a detailed analysis of the pulsational behavior of 50 HADS star candidates using high-precision photometric data from the Transiting Exoplanet Survey Satellite (TESS). We confirm 46 as genuine HADS variables, with 40 stars having their dominant frequencies identified for the first time. Among them, 7 pulsate solely in the fundamental mode; 21 exhibit the fundamental mode alongside at least one low-amplitude nonradial mode; 5 are pure double-mode pulsators (the fundamental and first-overtone modes), 13 show double-mode pulsations accompanied by additional low-amplitude nonradial modes. The remaining four stars are classified as other types of variables: two (TIC 69546708 and TIC 110937533) are confirmed hot subdwarfs, one (TIC 8765832) is a cataclysmic variable, and one (TIC 32302937) is a likely hot subluminous star, but it requires further spectroscopic confirmation. We investigate the period-luminosity (PL) relation, also known as the Leavitt law, for these 46 confirmed HADS stars, deriving a revised relation: $M_{V}= (-3.31 \pm0.39)~\mathrm{log}~P+(-1.68 \pm 0.39)$. This result is consistent with previous studies. Their distribution in the Hertzsprung-Russell diagram indicates that HADS stars are not strictly confined to be within a narrow instability strip previously found, but can extend beyond it, with a distribution toward lower temperatures. The refined classifications presented here establish a high-quality sample for precise asteroseismic modelling and enhance the potential for future machine-learning-assisted searches and classifications of HADS stars in large-scale photometric surveys.