Gravity-mode period spacings and near-core rotation rates of 611 γ Doradus stars with Kepler

Abstract

We report our survey of γ Dor stars from the 4-yr Kepler mission. These stars pulsate mainly in g modes and r modes, showing period-spacing patterns in the amplitude spectra. The period-spacing patterns are sensitive to the chemical composition gradients and the near-core rotation, hence they are essential for understanding the stellar interior. We identified period-spacing patterns in 611 γ Dor stars. Almost every star pulsates in dipole g modes, while about 30% of stars also show clear patterns for quadrupole g modes and 16% of stars present r mode patterns. We measure periods, period spacings, and the gradient of the period spacings. These three observables guide the mode identifications and can be used to estimate the near-core rotation rate. We find many stars are hotter and show longer period-spacing patterns than theory. Using the Traditional Approximation of Rotation (TAR), we inferred the asymptotic spacings, the near-core rotation rates, and the radial orders of the g and r modes. Most stars have a near-core rotation rate around 1 d −1 and an asymptotic spacing around 4000 s. We also find that many stars rotate more slowly than predicted by theory for unclear reasons. 11 stars show rotational splittings with fast rotation rates. We compared the observed slope-rotation relation with the theory and find a large spread. We detected rotational modulations in 58 stars and used them to derive the core-tosurface rotation ratios. The interiors rotate faster than the cores in most stars, but by no more than 5%.

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

“…However, if the core rotates more rapidly than the surface, which is consistent with the theory and observation (e.g. Rieutord 2006;Hypolite & Rieutord 2014;Li et al 2020), r modes will be more sensitive to the outer layers, whereas the g modes are more sensitive to the nearcore regions. This situation is rare in the observations but provides a new approach to detect radial differential rotation (Van Reeth et al 2018).…”

“…In addition to g modes, we also see Rossby modes (r modes) in about one-fifth of the γ Dor stars (Van Reeth et al 2016;Li et al 2019bLi et al , 2020. These modes are restored primarily by the Coriolis force (e.g.…”

“…The g-and r-mode patterns were identified by the algorithm described by Li et al (2019a). Mode identification was made based on the slope-period diagram founded on the 611 γ Dor stars by Li et al (2020), where the patterns clustered into different groups due to different kinds of modes. Fig.…”

“…We fitted the period spacings in each star using the TAR to obtain the near-core rotation rates (Van Reeth et al 2016;Li et al 2019bLi et al , 2020. The pulsation periods in the corotating frame are given by…”

Inverse tides in pulsating binary stars

“…All of our results apply equally well to γ Dor stars, and in fact several very slowly rotating γ-Dor stars in close binaries were recently discovered in Li et al (2020a). These include KIC 4142768 (P orb = 14.0 d, Prot = 2700 +1300 −660 d, see also Guo et al 2019) Lampens et al 2018 andLi et al 2020b). We note that KIC 4142768 is a heartbeat star in an eccentric orbit, with a periastron orbital period of Pperi = (1 − e) 3/2 P orb ≈ 3.8 d, which is more relevant when considering the strength of tidal forces.…”