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تسجيل مستخدم جديدThe effect of the centrifugal acceleration on period spacings of gravito-inertial modes in intermediate-mass stars
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The Kepler and TESS missions delivered high-precision, long-duration photometric time series for hundreds of main-sequence stars with gravito-inertial (g) pulsation modes. This high precision allows us to evaluate increasingly detailed theoretical stellar models. Recent theoretical work extended the traditional approximation of rotation (TAR), a framework to evaluate the effect of the Coriolis acceleration on g-modes, to include the effects of the centrifugal acceleration in the approximation of slightly deformed stars, which so far had mostly been neglected in asteroseismology. This extension of the TAR was conceived by rederiving the TAR in a centrifugally deformed, spheroidal coordinate system. We explore the effect of the centrifugal acceleration on g modes and assess its detectability in space-based photometry. We implement the new framework to calculate the centrifugal deformation of precomputed 1D spherical stellar structure models and compute the corresponding g-mode frequencies, assuming uniform rotation. The framework is evaluated for a grid of stellar structure models covering a relevant parameter space for observed g-mode pulsators. The centrifugal acceleration modifies the effect of the Coriolis acceleration on g modes, narrowing the equatorial band in which they are trapped. Furthermore, the centrifugal acceleration causes the pulsation periods and period spacings of the most common g modes (prograde dipole modes and r modes) to increase with values similar to the observational uncertainties in Kepler and TESS data. The effect of the centrifugal acceleration on g~modes is formally detectable in modern space photometry. Implementation of the new theoretical framework in stellar structure and pulsation codes will allow for more precise asteroseismic modelling of centrifugally deformed stars, to assess its effect on mode excitation, -trapping and -damping.
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Context. While rotation has a major impact on stellar structure and evolution, its effects are not well understood. Thanks to high- quality and long timebase photometric observations obtained with recent space missions, we are now able to study stell
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The relation of period spacing ($Delta P$) versus period ($P$) of dipole prograde g modes is known to be useful to measure rotation rates in the g-mode cavity of rapidly rotating $gamma$ Dor and slowly pulsating B (SPB) stars. In a rapidly rotating s
tar, an inertial mode in the convective core can resonantly couple with g modes propagative in the surrounding radiative region. The resonant coupling causes a dip in the $P$-$Delta P$ relation, distinct from the modulations due to the chemical composition gradient. Such a resonance dip in $Delta P$ of prograde dipole g modes appears around a frequency corresponding to a spin parameter $2f_{rm rot}{rm(cc)}/ u_{rm co-rot} sim 8-11$ with $f_{rm rot}$(cc) being the rotation frequency of the convective core and $ u_{rm co-rot}$ the pulsation frequency in the co-rotating frame. The spin parameter at the resonance depends somewhat on the extent of core overshooting, central hydrogen abundance, and other stellar parameters. We can fit the period at the observed dip with the prediction from prograde dipole g modes of a main-sequence model, allowing the convective core to rotate differentially from the surrounding g-mode cavity. We have performed such fittings for 16 selected $gamma$ Dor stars having well defined dips, and found that the majority of $gamma$ Dor stars we studied rotate nearly uniformly, while convective cores tend to rotate slightly faster than the g-mode cavity in less evolved stars.
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n the radiative zone of a differentially rotating star. We consider a simplified model where the radiative zone of the star is a linearly stratified rotating fluid within a spherical shell, with differential rotation due to baroclinic effects. We solve the eigenvalue problem with high-resolution spectral computations and determine the propagation domain of the waves through the theory of characteristics. We explore the propagation properties of two kinds of modes: those that can propagate in the entire shell and those that are restricted to a subdomain. Some of the modes that we find concentrate kinetic energy around short-period shear layers known as attractors. We describe various geometries for the propagation domains, conditioning the surface visibility of the corresponding modes.
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