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On the origin of sinusoidal brightness variations in F to O-type stars through radial velocities

E. Šipková, M. Skarka, M. Vaňko, V. Chmelař, T. Pribulla, Z. Mikulášek

TL;DR

This study addresses the origin of sinusoidal brightness variations in hot main-sequence stars (spectral types F–O) by distinguishing binarity, pulsations, and rotational spot modulation through a joint analysis of TESS photometry and high-resolution spectroscopy. Starting from a large TIC-based catalog, the authors define a subset of 108 targets with clean low-frequency sinusoidal variability and perform spectroscopic follow-up on 35 of them using northern and southern facilities, deriving radial velocities via cross-correlation. The objects are categorized into binaries (SB1/SB2), pulsators, spotted-star candidates, or uncertain cases based on the interplay between light curves and RVs, refined period analyses with Period04, and spectral features; the results reveal that at least half of sinusoidal hot-star variables are binaries, with 8 new binaries identified. The work highlights the necessity of object-by-object classification, as photometry alone can be insufficient to reveal the true variability mechanism, and it provides refined multiplicity and variability statistics for hot, radiative-envelope stars. Overall, the study demonstrates the value of integrating time-domain photometry with targeted spectroscopy to unravel the origins of stellar variability and informs future surveys and interpretation of hot-star light curves.

Abstract

Stellar variability may originate from various phenomena such as binarity, pulsations, or rotation. These mechanisms can induce flux variations of similar magnitudes, shapes, and periods. We aim to determine mechanisms responsible for the sinusoidal variations in main-sequence stars hotter than 6500 K. We conducted our analysis using TESS long-cadence data complemented with high-resolution spectra from three spectrographs. From the initial sample of almost 46000 objects, we selected 35 targets for spectroscopic follow-up. Comparison of light curves and radial velocity curves allowed for robust classification of these targets. Among the 35 selected objects, 18 displayed variability, suggesting the presence of a companion (including the discovery of 7 new binary systems and 1 candidate for a triple-star system), 1 was identified as a new pulsator, 9 as new candidates for spotted stars, and 7 objects had uncertain classification. Our analysis shows that at least half of randomly selected stars with sinusoidal brightness variations are binaries. The presented results illustrate the need for an individual approach to stellar classification, especially in cases where the photometric data alone is insufficient for determining the underlying phenomena behind the observed variations.

On the origin of sinusoidal brightness variations in F to O-type stars through radial velocities

TL;DR

This study addresses the origin of sinusoidal brightness variations in hot main-sequence stars (spectral types F–O) by distinguishing binarity, pulsations, and rotational spot modulation through a joint analysis of TESS photometry and high-resolution spectroscopy. Starting from a large TIC-based catalog, the authors define a subset of 108 targets with clean low-frequency sinusoidal variability and perform spectroscopic follow-up on 35 of them using northern and southern facilities, deriving radial velocities via cross-correlation. The objects are categorized into binaries (SB1/SB2), pulsators, spotted-star candidates, or uncertain cases based on the interplay between light curves and RVs, refined period analyses with Period04, and spectral features; the results reveal that at least half of sinusoidal hot-star variables are binaries, with 8 new binaries identified. The work highlights the necessity of object-by-object classification, as photometry alone can be insufficient to reveal the true variability mechanism, and it provides refined multiplicity and variability statistics for hot, radiative-envelope stars. Overall, the study demonstrates the value of integrating time-domain photometry with targeted spectroscopy to unravel the origins of stellar variability and informs future surveys and interpretation of hot-star light curves.

Abstract

Stellar variability may originate from various phenomena such as binarity, pulsations, or rotation. These mechanisms can induce flux variations of similar magnitudes, shapes, and periods. We aim to determine mechanisms responsible for the sinusoidal variations in main-sequence stars hotter than 6500 K. We conducted our analysis using TESS long-cadence data complemented with high-resolution spectra from three spectrographs. From the initial sample of almost 46000 objects, we selected 35 targets for spectroscopic follow-up. Comparison of light curves and radial velocity curves allowed for robust classification of these targets. Among the 35 selected objects, 18 displayed variability, suggesting the presence of a companion (including the discovery of 7 new binary systems and 1 candidate for a triple-star system), 1 was identified as a new pulsator, 9 as new candidates for spotted stars, and 7 objects had uncertain classification. Our analysis shows that at least half of randomly selected stars with sinusoidal brightness variations are binaries. The presented results illustrate the need for an individual approach to stellar classification, especially in cases where the photometric data alone is insufficient for determining the underlying phenomena behind the observed variations.
Paper Structure (14 sections, 2 equations, 11 figures, 5 tables)

This paper contains 14 sections, 2 equations, 11 figures, 5 tables.

Table of Contents

  1. Introduction
  2. Sample definition
  3. Initial sample
  4. Finalisation of sample
  5. Spectroscopic observations
  6. Analysis
  7. Binary stars
  8. Pulsating stars
  9. Candidates for spots
  10. Uncertain classification
  11. Discussion
  12. Conclusions
  13. Classification table
  14. Measured relative radial velocities

Figures (11)

  • Figure 1: Residuals after fitting the data with a single-sine (left panel) and a two-sine (right-hand panel) function. The figure contains standard deviations of residuals and their ratio used for identifying sinusoidal variability.
  • Figure 2: Example of LC (top plot) showing original (gray dots) and binned data (black crosses) and RV curve (bottom plot) for a spectroscopic binary with two visible components - TIC 257456854.
  • Figure 3: CCF of TIC 14400891. This object is a candidate for a triple star system, based on the number of correlation peaks.
  • Figure 4: Comparison of LC (top plots) showing original (gray dots) and binned data (black crosses) and RVs (bottom plots) for a spectroscopic binary with one visible component phased with 1P (first column) and 2P (second column) - TIC 21673730.
  • Figure 5: RV curve of TIC 174214184 measured with OES, where points highlighted with red show corresponding spectra zoomed on the $\mathrm{H\alpha}$ that shows lines of both components.
  • ...and 6 more figures