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

Taozhi Yang, Zhaoyu Zuo

TL;DR

The study addresses the challenge of accurately classifying high-amplitude δ Scuti (HADS) stars to enable precise asteroseismic inferences. It analyzes 50 HADS candidates with high-precision TESS photometry, identifying 46 as genuine HADS and determining the dominant pulsation modes for most, including mono-mode, F+non-radial, and F+1O configurations, with 4 misclassifications reclassified as non-HADS (hot subdwarfs and related objects). A revised period-luminosity relation is derived as $M_V = (-3.31 \pm 0.39) \log P + (-1.68 \pm 0.39)$, and the HR diagram placement reveals HADS spanning a broader temperature range than the traditional instability strip, challenging the notion of a narrow HADS IS. The refined classifications yield a high-quality sample for future detailed modelling and provide a solid benchmark for machine-learning–assisted searches of HADS in large photometric surveys.

Abstract

Asteroseismic modelling of high-amplitude $δ$ 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.

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

TL;DR

The study addresses the challenge of accurately classifying high-amplitude δ Scuti (HADS) stars to enable precise asteroseismic inferences. It analyzes 50 HADS candidates with high-precision TESS photometry, identifying 46 as genuine HADS and determining the dominant pulsation modes for most, including mono-mode, F+non-radial, and F+1O configurations, with 4 misclassifications reclassified as non-HADS (hot subdwarfs and related objects). A revised period-luminosity relation is derived as , and the HR diagram placement reveals HADS spanning a broader temperature range than the traditional instability strip, challenging the notion of a narrow HADS IS. The refined classifications yield a high-quality sample for future detailed modelling and provide a solid benchmark for machine-learning–assisted searches of HADS in large photometric surveys.

Abstract

Asteroseismic modelling of high-amplitude 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: . 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.

Paper Structure

This paper contains 13 sections, 4 equations, 11 figures.

Table of Contents

  1. Introduction
  2. TESS observations and Data Reduction
  3. Frequency Analysis and Mode Identification
  4. Results
  5. Mono-mode HADS stars
  6. HADS stars with F mode and non-radial modes
  7. Double-mode HADS stars
  8. Double-mode HADS stars with non-radial modes
  9. Other types of variable stars
  10. Period-Luminosity Relation
  11. Location in H-R Diagram
  12. Discussion
  13. Summary

Figures (11)

  • Figure 1: Top pannel: A portion of light curve of TIC 710783 for about 3 days; Middle pannel: Phased diagram (folded by the dominant frequency $f = 12.74450$ c/day); Lower pannel: Amplitude spectra with a frequency range of $0 < f < 80$ c/day.
  • Figure 2: The upper panel shows a portion of the light curve of TIC 17153995 for about 3 days; The middle panel shows the phase diagram folded by the fundamental frequency $f = 8.54480$ c/day; The lower panel shows the Fourier amplitude spectra.
  • Figure 3: The upper panel shows a portion of the light curve of TIC 16283570 for about 3 days; The middle panel shows the phase diagram folded by the fundamental frequency $f = 11.02399$ c/day; The lower panel shows the Fourier amplitude spectra.
  • Figure 4: The upper panel shows a portion of the light curve of TIC 7082633 for about 3 days; The middle panel shows the phase diagram folded by the fundamental frequency $f = 10.32293$ c/day; The lower panel shows the Fourier amplitude spectra.
  • Figure 5: The Peterson diagram of the double-mode HADS stars. Red squares represent 5 pure double-mode HADS stars, blue triangles are 13 HADS in this group. The shaded bands represent the period ratios of the first three overtone modes to fundamental mode, as well as the period ratio of the second overtone to first overtone mode 1979ApJ...227..935S.
  • ...and 6 more figures