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BlackGEM observations of compact pulsating stars: Mode identification for the DOV PG 1159-035 using multi-colour photometry

P. Ranaivomanana, C. Johnston, M. Uzundag, P. J. Groot, T. Kupfer, S. Bloemen, P. M. Vreeswijk, J. C. J. van Roestel, D. L. A. Pieterse, J. Paice, A. Kosakowski, G. Ramsay, C. Aerts

Abstract

While space-based telescopes offer unparalleled precision for asteroseismology, ground-based observations remain crucial for identifying compact pulsator candidates and enabling their pulsational study through multi-colour photometry. The BlackGEM telescope array significantly enhances the detection and characterisation possibilities for compact pulsators that tend to be much fainter than dwarf or giant pulsators. Using BlackGEM multi-colour photometry of the hot pre-white dwarf PG 1159-035, we demonstrate its capability to detect short, multi-periodic pulsations with amplitudes down to a few milli-magnitudes. The primary aim of this study is to establish the feasibility of pulsation mode identification in hot subdwarfs and white dwarfs via mode amplitude-ratio analysis derived from BlackGEM multi-colour observations. Pulsation frequencies were extracted from our target using iterative pre-whitening analysis. To validate our data-driven mode identification concept using multi-colour photometry, we used the well-studied hot pre-white dwarf PG 1159-035, with previously identified pulsation modes, as a prototypical object that served for validation. The pre-whitening analysis using BlackGEM's standard q-, u-, and i-band light curves of PG 1159-035 revealed pulsation frequencies of l=1 and l=2 modes, consistent with values obtained from the literature. Subsequent amplitude ratio calculations resulted in discernible distributions for the l=1 and l=2 modes. The future assembly of more BlackGEM amplitude ratios for well-known white dwarfs with already identified modes will lead to density estimators suitable for identifying newly detected modes in known or as-yet-undiscovered pulsators. Our proof-of-concept study paves the way for large-scale asteroseismic analyses of optically faint compact pulsating stars using ground-based facilities, such as BlackGEM.

BlackGEM observations of compact pulsating stars: Mode identification for the DOV PG 1159-035 using multi-colour photometry

Abstract

While space-based telescopes offer unparalleled precision for asteroseismology, ground-based observations remain crucial for identifying compact pulsator candidates and enabling their pulsational study through multi-colour photometry. The BlackGEM telescope array significantly enhances the detection and characterisation possibilities for compact pulsators that tend to be much fainter than dwarf or giant pulsators. Using BlackGEM multi-colour photometry of the hot pre-white dwarf PG 1159-035, we demonstrate its capability to detect short, multi-periodic pulsations with amplitudes down to a few milli-magnitudes. The primary aim of this study is to establish the feasibility of pulsation mode identification in hot subdwarfs and white dwarfs via mode amplitude-ratio analysis derived from BlackGEM multi-colour observations. Pulsation frequencies were extracted from our target using iterative pre-whitening analysis. To validate our data-driven mode identification concept using multi-colour photometry, we used the well-studied hot pre-white dwarf PG 1159-035, with previously identified pulsation modes, as a prototypical object that served for validation. The pre-whitening analysis using BlackGEM's standard q-, u-, and i-band light curves of PG 1159-035 revealed pulsation frequencies of l=1 and l=2 modes, consistent with values obtained from the literature. Subsequent amplitude ratio calculations resulted in discernible distributions for the l=1 and l=2 modes. The future assembly of more BlackGEM amplitude ratios for well-known white dwarfs with already identified modes will lead to density estimators suitable for identifying newly detected modes in known or as-yet-undiscovered pulsators. Our proof-of-concept study paves the way for large-scale asteroseismic analyses of optically faint compact pulsating stars using ground-based facilities, such as BlackGEM.
Paper Structure (9 sections, 8 figures, 6 tables)

This paper contains 9 sections, 8 figures, 6 tables.

Table of Contents

  1. Introduction
  2. Data and methods
  3. Target
  4. Pulsations extractions
  5. Results
  6. Combination frequencies and resonant mode coupling
  7. Amplitude ratios
  8. Conclusion and future prospects
  9. Additional material

Figures (8)

  • Figure 1: Number of observations per month per filter for PG 1159--035's BlackGEM light curve.
  • Figure 2: Periodograms of the first five iterations and the last iteration in the iterative pre-whitening processes of the frequencies obtained from the $q$ band.
  • Figure 3: Amplitude evolution of the K2 triplet mode, estimated using BlackGEM $q$-, $u$-, and $i$-band light curves. The x-axis represents the median of the time-series in each of the four time-series bins, while the y-axis their corresponding amplitudes.
  • Figure 4: Relative amplitude as a function of relative phase of the two combination frequencies and the triplet mode. Parameter $f(m=0)$ represents the frequency of the central component of the triplet mode.
  • Figure 5: Amplitude ratio distribution of the eight pulsation modes in the $q$-band-extracted frequencies. The left panel shows the amplitude ratios derived from $q$-band frequencies, while the middle and right panels correspond to amplitude ratios estimated by imposing the K2 and WET frequencies, respectively.
  • ...and 3 more figures