DOI: 10.5281/zenodo.7555867
title: Tidally perturbed g-mode pulsations in a sample of close eclipsing binaries

description: Description:<br> Reduced Kepler and TESS light curves of KIC 3228863, KIC 3341457, KIC 4947528, KIC 9108579, and<br> KIC 12785282, as well as various data products obtained at different steps of the analysis presented in Van Reeth<br> et al. (2023): the residual pulsation light curves (after subtracting the harmonic model for the binarity), the<br> optimised prewhitened (Kepler) frequency lists, measured g-mode patterns, and detected tidal g-mode<br> perturbations (both measured directly from orbital-phase-binned data and reconstructed using detected<br> orbital-frequency-spaced multiplets). Abstract:<br> Context. Thanks to the high-precision photometry from space missions such as Kepler and TESS, tidal<br> perturbations and tilting of pulsations have been detected in more than a dozen binary systems. However, only<br> two of these were gravity-mode (g-mode) pulsators.<br> Aims. We aim to detect tidally perturbed g modes in additional binary systems and characterise them<br> observationally.<br> Methods. We perform a custom data reduction of the available Kepler and TESS photometry of a well-studied,<br> published sample of 35 binary systems with gamma Doradus (gamma Dor) pulsators. For each target, we model<br> the binary signal using a sum of 100 sine waves, with frequencies at orbital harmonics, and measure significant<br> pulsation frequencies in an iterative prewhitening analysis of the residual light curve. Pulsations are<br> labelled as tidally perturbed g modes if they are part of both period-spacing patterns and multiplets spaced by<br> integer multiples of the orbital frequency. After visual inspection and confirmation, the properties of these<br> targets and g modes are characterised.<br> Results. We detect tidally perturbed g-mode pulsations for five short-period binaries that are circularised and<br> (almost) synchronously rotating: KIC 3228863, KIC 3341457, KIC 4947528, KIC 9108579, and KIC 12785282.<br> Tidally perturbed g modes that occur within the same star and have the same mode identification (k,m), are found<br> to have near-identical relative amplitude and phase modulations, which are within their respective 1-sigma<br> uncertainties also identical for the Kepler and TESS photometric passbands. By contrast, pulsations with<br> different mode identification (k,m) are found to exhibit different modulations. Moreover, the observed<br> amplitude and phase modulations are correlated, indicating that the binary tides primarily distort the g-mode<br> amplitudes on the stellar surface. The phase modulations are then primarily a geometric effect of the<br> integration of the stellar flux over the visible stellar surface. All selected binaries also exhibit signal<br> that resembles rotational modulation in the Fourier domain. In the case of KIC 3228863, this is caused by the<br> presence of the known tertiary component, and for the other systems we hypothesise that it is caused by<br> temperature variations on the stellar surface. Alternatively, the signal can be overstable convective modes in<br> the stellar core or belong to the non-pulsating companion.<br> Conclusions. While g-mode pulsation periods are known to be a direct probe of the deep interior stellar<br> structure, the binary tides which cause the pulsation modulations are dominant in the outer stellar layers.<br> Hence, in future tidally perturbed g modes may allow us to do core-to-surface asteroseismic modelling of<br> tidally distorted stars.
description: TVR and DMB gratefully acknowledge funding from the research foundation Flanders (FWO) by means of junior and senior postdoctoral fellowships with grant agreements Nrs. 12ZB620N and 1286521N, respectively, and FWO long stay travel grants Nrs. V414021N and V411621N, respectively. JVB acknowledges receiving support from the Research Foundation Flanders (FWO) under grant agreement Nr. V421221N. The research leading to these results also received partial funding from the KU Leuven Research Council (grant C16/18/005: PARADISE), and was supported in part by the National Science Foundation under Grant No. NSF PHY-1748958. CJ gratefully acknowledges support from the Netherlands Research School of Astronomy (NOVA). This paper includes data collected with the Kepler and TESS missions, obtained from the MAST data archive at the Space Telescope Science Institute (STScI). Funding for the Kepler and TESS missions are provided by NASA's Science Mission Directorate and the NASA Explorer Program, respectively. We thank the whole teams for the development and operations of these missions. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Support to MAST for these data is provided by the NASA Office of Space Science via grant NAG5-7584 and by other grants and contracts. This research also made use of the SIMBAD database, operated at CDS, Strasbourg, France, the SAO/NASA Astrophysics Data System, and the VizieR catalogue access tool, CDS, Strasbourg, France. The data analysis was done using Astropy (a community-developed core Python package for Astronomy; Astropy Collaboration et al. 2013, 2018), Astroquery (Ginsburg et al. 2019), Lightkurve (a Python package for Kepler and TESS data analysis; Lightkurve Collaboration et al. 2018), lmfit (Newville et al. 2019), Matplotlib (the Python library for publication quality graphics; Hunter 2007), Numpy (Harris et al. 2020), and Scipy (Virtanen et al. 2020).