Tidally perturbed g-mode pulsations in a sample of close eclipsing binaries

Description:
    Reduced Kepler and TESS light curves of KIC 3228863, KIC 3341457, KIC 4947528, KIC 9108579, and
    KIC 12785282, as well as various data products obtained at different steps of the analysis presented in Van Reeth
    et al. (2023): the residual pulsation light curves (after subtracting the harmonic model for the binarity), the
    optimised prewhitened (Kepler) frequency lists, measured g-mode patterns, and detected tidal g-mode
    perturbations (both measured directly from orbital-phase-binned data and reconstructed using detected
    orbital-frequency-spaced multiplets).

Abstract:
    Context. Thanks to the high-precision photometry from space missions such as Kepler and TESS, tidal
    perturbations and tilting of pulsations have been detected in more than a dozen binary systems. However, only
    two of these were gravity-mode (g-mode) pulsators.
    Aims. We aim to detect tidally perturbed g modes in additional binary systems and characterise them
    observationally.
    Methods. We perform a custom data reduction of the available Kepler and TESS photometry of a well-studied,
    published sample of 35 binary systems with gamma Doradus (gamma Dor) pulsators. For each target, we model
    the binary signal using a sum of 100 sine waves, with frequencies at orbital harmonics, and measure significant
    pulsation frequencies in an iterative prewhitening analysis of the residual light curve. Pulsations are
    labelled as tidally perturbed g modes if they are part of both period-spacing patterns and multiplets spaced by
    integer multiples of the orbital frequency. After visual inspection and confirmation, the properties of these
    targets and g modes are characterised.
    Results. We detect tidally perturbed g-mode pulsations for five short-period binaries that are circularised and
    (almost) synchronously rotating: KIC 3228863, KIC 3341457, KIC 4947528, KIC 9108579, and KIC 12785282.
    Tidally perturbed g modes that occur within the same star and have the same mode identification (k,m), are found
    to have near-identical relative amplitude and phase modulations, which are within their respective 1-sigma
    uncertainties also identical for the Kepler and TESS photometric passbands. By contrast, pulsations with
    different mode identification (k,m) are found to exhibit different modulations. Moreover, the observed
    amplitude and phase modulations are correlated, indicating that the binary tides primarily distort the g-mode
    amplitudes on the stellar surface. The phase modulations are then primarily a geometric effect of the
    integration of the stellar flux over the visible stellar surface. All selected binaries also exhibit signal
    that resembles rotational modulation in the Fourier domain. In the case of KIC 3228863, this is caused by the
    presence of the known tertiary component, and for the other systems we hypothesise that it is caused by
    temperature variations on the stellar surface. Alternatively, the signal can be overstable convective modes in
    the stellar core or belong to the non-pulsating companion.
    Conclusions. While g-mode pulsation periods are known to be a direct probe of the deep interior stellar
    structure, the binary tides which cause the pulsation modulations are dominant in the outer stellar layers.
    Hence, in future tidally perturbed g modes may allow us to do core-to-surface asteroseismic modelling of
    tidally distorted stars.