Probing stellar rotation in the Pleiades with gravity-mode pulsators

TL;DR

The paper identifies and analyzes gravity-mode pulsators in the Pleiades to measure near-core rotation in young, upper-main-sequence stars using TESS data. It reports 28 g-mode pulsators (including 19 hybrids) among 105 targets, with 3 stars showing clear period-spacing patterns enabling direct f_rot and Pi_0 determinations, while the rest yield f_rot from the dominant mode; these near-core rotations span 1–3 d^-1 with no strong mass dependence. Buoyancy periods Pi_0 across the Pleiades are broadly similar to those in the NGC 2516 cluster, consistent with a similar asteroseismic age, and supporting the Pleiades as a valuable ensemble asteroseismic benchmark. By combining asteroseismic, photometric, and spectroscopic rotation indicators for 62 stars, the work reveals a wide rotation dispersion on the upper main sequence and highlights the Pleiades as a key laboratory for probing angular momentum transport in young stars and for calibrating rotating stellar models.

Abstract

Due to their proximity, the Pleiades are an important benchmark open cluster. Despite its status, asteroseismic analyses of its members are rare. In particular, the gravity-mode (g-mode) pulsators, which allow inference of stellar near-core properties have not been analysed yet. We aim to identify and analyse the population of g-mode pulsators in the Pleiades. Our focus lies on the internal rotation as measured from asteroseismology to obtain a well defined sample of stellar rotation on the early main sequence. Based on full-frame images from the Transiting Exoplanet Survey Satellite (TESS), we constructed light curves for intermediate-mass Pleiades members and searched for g-mode pulsators among them. For pulsators exhibiting period spacing patterns, we determined their near-core rotation rate and buoyancy periods. For all other g-mode pulsators, we estimated the near-core rotation rate based on the dominant mode frequency to obtain a comprehensive rotation rate distribution. Among our 105 target stars, we find 28 g-mode pulsators distributed across the entire upper main sequence, 19 of which are hybrid pulsators, but only three stars exhibit period spacing patterns in the current TESS data. The near-core rotation rates in A- and early F-type members are distributed between 1 and 3 d$^{-1}$ without any clear mass-dependence. This distribution is much broader than the one in the similar open cluster NGC 2516. A comparison of the buoyancy periods shows that the Pleiades and NGC 2516 are of similar asteroseismic age. With the large population of g-mode and hybrid pulsators, the Pleiades constitute a valuable asteroseismic benchmark cluster, reaffirming its important role in stellar astrophysics.

Figures (10)

• Figure 1: Colour-magnitude diagram of the Pleiades overlaid with rotating isochrones at 125 Myr. In orange, we show MIST2016ApJS..222....8D2016ApJ...823..102C and in blue PARSEC2022AA...665A.126N. The green isochrone is the MIST model with the YBC bolometric corrections 2019AA...632A.105C. The inset highlights the bump around spectral type F. The top axis indicates the spectral type.
• Figure 2: Colour-magnitude diagram of the upper main sequence of the Pleiades. We mark our discovered g-mode pulsators with orange and known p-mode pulsators from Bedding2023 with black dots. The dotted and dashed lines crossing the cluster sequence, indicate the $\gamma$ Dor and $\delta$ Sct instability strips, respectively 2004AA...414L..17D2019MNRAS.485.2380M. The grey lines show the isochrones from Fig. \ref{['fig:clusterCMD']} with MIST dashed, PARSEC dotted, and MIST with the YBC bolometric corrections adopted in PARSEC dash-dotted. Stars with proper names are labelled.
• Figure 3: Periodograms of Pleiades g-mode pulsators ordered by their intrinsic colour with the hottest stars (SPB stars) at the top and the typical $\gamma$ Dor pulsators at the bottom. The orange dashed lines mark the derived near-core rotation periods. The amplitude of each periodogram is normalized by the dominant g-mode amplitude. The names of stars for which we constructed period-spacing patterns are highlighted in orange.
• Figure 4: Period spacing patterns for the three Pleiads with regularly-spaced gravity modes. The top panels show the frequency spectra with the extracted periods marked by crosses. The selected modes of the period spacing pattern are shown by solid orange lines. The best-fit asymptotic pulsation solution is indicated by dashed lines. The lower panel shows the observed period spacing pattern (crosses and solid line) together with the best fit (dashed) for $f_\mathrm{rot}$ and $\Pi_0$.
• Figure 5: Stellar rotation rates for upper main-sequence stars in the Pleiades. Asteroseismic near-core rotation rates are shown with large symbols, while surface rotation rates are shown with small symbols. The different shapes correspond to the different methods. Squares indicate near-core rotation inferred from period spacing patterns using the traditional approximation of rotation, circles are based on the dominant mode frequency of the g-mode pulsators. Photometric surface rotation rates are marked with plusses for stars from Rebull2016 and with crosses for new detection in this work. Finally, we show rotation rates estimated from $v\sin i$ measurements in the Pleiades with triangles. Stars with both surface and near-core rotation rates are connected by lines. The grey hatched areas indicate the approximate range of the theoretical $\gamma$ Dor 2004AA...414L..17D and observational $\delta$ Sct 2019MNRAS.485.2380M instability strips. The asteroseismic uncertainties are mostly within the symbol sizes and have been omitted for clarity.