The effect of tides on near-core rotation: analysis of 35 Kepler γ Doradus stars in eclipsing and spectroscopic binaries

Abstract

We systematically searched for gravity- and Rossby-mode period spacing patterns in Kepler eclipsing binaries with γ Doradus pulsators. These stars provide an excellent opportunity to test the theory of tidal synchronisation and angular momentum transport in F- and A-type stars. We discovered 35 systems that show clear patterns, including the spectroscopic binary KIC 10080943. Combined with 45 non-eclipsing binaries with γ Dor components that have been found using pulsation timing, we measured their near-core rotation rates and asymptotic period spacings. We find that many stars are tidally locked if the orbital periods are shorter than 10 days, in which the near-core rotation periods given by the traditional approximation of rotation (TAR) are consistent with the orbital period. Compared to the single stars, γ Dor stars in binaries tend to have slower near-core rotation rates, likely a consequence of tidal spin-down. We also find three stars that have extremely slow near-core rotation rates. To explain these, we hypothesise that unstable tidally excited oscillations can transfer angular momentum from the star to the orbit, and slow the star below synchronism, a process we refer to as ‘inverse tides’.

Tango of celestial dancers: A sample of detached eclipsing binary systems containingg-mode pulsating components

“…However, we list them here for completeness. KIC9850387 was first studied by Zhang et al (2020), who claimed that the system was a pre-main-sequence SB1 eclipsing system containing a hybrid p-and g-mode pulsator, and reported the detection of an = 1 period-spacing pattern with a mean period spacing of 2756.2 ± 0.8 s. This system was also studied by Li et al (2020a), who had reported a = 1, m = 1 and a = 2, m = 2 periodspacing pattern, with Π 0 = 3894 ± 7 s and a core-rotation rate f rot,core = 0.0053 d −1 .…”

“…The 45 systems without a reference in Table A.1 are therefore eclipsing binary systems whose g-mode pulsational characteristics were discovered during this study. Li et al (2020a) performed a study of 35 Kepler eclipsing and spectroscopic binaries in which they identified clear periodspacing patterns, with the majority of those selected from the catalogue of Gaulme & Guzik (2019). 11 of those are also in our sample as part of the 24 systems whose periodograms contain dense clusters of g-mode frequencies.…”

“…Morph = −1); (4) Undefined KIC temperatures (T eff = −1); (5) Higher-order eclipsing system (the quintuple system KIC4150611). We posit that our catalogue and that of Li et al (2020a) are complementary, as we include all g-mode (and hybrid p-and g-mode) pulsators independently identified in detached eclipsing binaries, with both pulsational and orbital characterisation.…”

“…the polyfit models described in Prša et al 2011) or a binned model of the light curve (e.g. Li et al 2020a) may inadvertently result in the removal of pulsational variation, and as such we chose not to adopt such techniques.…”

“…This would enable two independent calibrations of the amount of coreboundary mixing that would have to be included in the evolutionary models in order to match either the dynamical parameters or the observed g-mode period-spacing patterns, enabling simultaneous confrontation of dynamical, evolutionary and asteroseismic parameters. In addition, there has thus far only been one ensemble study of eclipsing binaries with g-mode periodspacing patterns (Li et al 2020a), which is a rather curious phenomenon considering that hundreds of stars with g-mode period-spacing patterns have been discovered (Li et al 2020b).…”