Gravity modes in rapidly rotating stars

Ballot, J.; Lignières, F.; Reese, D. R.; Rieutord, M.

doi:10.1051/0004-6361/201014426

Cited by 81 publications

(86 citation statements)

References 30 publications

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“…Finally, since our goal is to obtain a complete and coherent picture of the transport of angular momentum in stellar radiation zones for every stellar type or evolutionary stage, it will be important to extend this work to cases of gravito-inertial waves, where the action of Coriolis and centrifugal accelerations is considered (e.g. Lee & Saio 1997;Dintrans & Rieutord 2000;Mathis 2009;Ballot et al 2010) and magneto-gravito-inertial waves, when radiation zones are magnetized (e.g. …”

Section: Resultsmentioning

confidence: 99%

Coupling between internal waves and shear-induced turbulence in stellar radiation zones: the critical layers

Alvan

Mathis

Decressin

2013

A&A

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Context. Internal gravity waves (IGW) are known as one of the candidates for explaining the angular velocity profile in the Sun and in solar-type main-sequence and evolved stars due to their role in the transport of angular momentum. Our contribution deals with critical layers, which are defined as the locations where the Doppler-shifted frequency of the wave approaches zero (i.e., they correspond to corotation resonances). Aims. The IGW propagate through stably stratified radiative regions, where they extract or deposit angular momentum through two processes: radiative and viscous dampings and critical layers. Our goal is to obtain a complete picture of the effects of these processes. Methods. First, we expose a mathematical resolution of the equation of propagation for IGW in adiabatic and non-adiabatic cases near critical layers. Then, the use of a dynamical stellar evolution code, which treats the secular transport of angular momentum, allows us to apply these results to the case of a solar-like star. Results. The analysis reveals two cases depending on the value of the Richardson number at critical layers: a stable one, where IGW are attenuated as they pass through a critical level, and an unstable turbulent case, where they can be reflected/transmitted by the critical level with a coefficient larger than one. Such over-reflection/transmission can have strong implications on our vision of angular momentum transport in stellar interiors. Conclusions. This paper highlights the existence of two regimes defining the interaction between an IGW and a critical layer. An application exposes the effect of the first regime, showing a strengthening of the damping of the wave. Moreover, this work opens up new ways concerning the coupling between IGW and shear instabilities in stellar interiors.

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Section: Resultsmentioning

confidence: 99%

Coupling between internal waves and shear-induced turbulence in stellar radiation zones: the critical layers

Alvan

Mathis

Decressin

2013

A&A

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“…The Coriolis acceleration (and the centrifugal one) therefore modifies the propagation of internal waves as soon as the 2Ω/ω c ratio increases (ω c is the frequency at which the internal wave is excited). The induced transport of angular momentum and mixing is modified in two ways: -First, internal waves are trapped in an equatorial belt when ω c < 2Ω because of the Coriolis acceleration action (Lee & Saio 1997;Mathis 2009;Ballot et al 2010). The convective kinetic energy is then transmitted less efficiently to the internal waves in the radiative envelope.…”

Section: Internal Wavesmentioning

confidence: 99%

Seismic modelling of the late Be stars HD 181231 and HD 175869 observed with CoRoT: a laboratory for mixing processes

Neiner

Mathis

Saio

et al. 2012

A&A

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Context. HD 181231 and HD 175869 are two late rapidly rotating Be stars, which have been observed using high-precision photometry with the CoRoT satellite during about five consecutive months and 27 consecutive days, respectively. An analysis of their light curves, by Neiner and collaborators and Gutiérrez-Soto and collaborators respectively, showed that several independent pulsation g-modes are present in these stars. Fundamental parameters have also been determined by these authors using spectroscopy. Aims. We aim to model these results to infer seismic properties of HD 181231 and HD 175869, and constrain internal transport processes of rapidly rotating massive stars. Methods. We used an adiabatic (NRO) and a non-adiabatic (Tohoku) oscillation code that accounts for the combined action of Coriolis and centrifugal accelerations on stellar pulsations as needed for rapid rotator modelling. We coupled these codes with a 2D (ROTORC) stellar structure model to take the rotational deformation of the star into account. The action of transport processes was parametrised with the mixing parameter α ov , which represents the "non-standard" extension of the convective core, and determined by matching observed pulsation frequencies assuming a single star evolution scenario. In a second step, we used (Geneva) evolution models to evaluate the contribution of the secular rotational transport and mixing processes in the radiative envelope. A Monte Carlo analysis of spectropolarimetric data was also performed to examine the role of a potential fossil magnetic field. Finally, based on state-of-the-art modelling of penetrative convection and internal waves, we unravelled their respective contribution to the needed "non-standard" mixing.Results. We find that extra mixing of α ov = 0.3−0.35H p is needed in HD 181231 and HD 175869 to match the observed frequencies with those of prograde sectoral g-modes. We also detect the possible presence of r-modes. We investigated the respective contributions of several transport processes to this mixing: the hydrodynamical processes in particular the meridional circulation and shear-induced turbulence caused by the radiative envelope differential rotation, the possible magnetic field, the penetrative convection at the top of the convective core, and the transport by internal waves. Conclusions. We showed that the extension of the convective core needed to match observations and models may be explained by mixing induced by the penetrative movements at the bottom of the radiative envelope and by the secular hydrodynamical transport processes induced by the rotation in the envelope. We showed how asteroseismology opens a new door to probe transport processes in stellar interiors.

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“…While this can be done using the traditional approximation for modes whose frequency is above twice the rotation frequency (Aerts & Dupret 2012;Ballot et al 2012), the lowest frequency modes of HD 48977 correspond to so-called gravito-inertial waves and require a treatment that does not rely on perturbative methods (Ballot et al 2010).…”

Section: Discussionmentioning

confidence: 99%

High-precision CoRoT space photometry and fundamental parameter determination of the B2.5V star HD 48977

Thoul

Degroote

Catala

et al. 2013

A&A

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We present the CoRoT light curve of the bright B2.5V star HD 48977 observed during a short run of the mission in 2008, as well as a high-resolution spectrum gathered with the HERMES spectrograph at the Mercator telescope. We use several time series analysis tools to explore the nature of the variations in the light curve. We performed a detailed analysis of the spectrum of the star to determine its fundamental parameters and its element abundances. We find a large number of high-order g-modes, and one rotationally induced frequency. We find stable low-amplitude frequencies in the p-mode regime as well. We conclude that HD 48977 is a new slowly pulsating B star with fundamental parameters found to be T eff = 20 000 ± 1000 K and log g = 4.2 ± 0.1. The element abundances are similar to those found for other B stars in the solar neighbourhood. HD 48977 was observed during a short run of the CoRoT satellite implying that the frequency precision is insufficient to perform asteroseismic modelling of the star. Nevertheless, we show that a longer time series of this star would be promising for such modelling. Our present study contributes to a detailed mapping of the instability strips of B stars in view of the dominance of g-mode pulsations in the star, several of which occur in the gravito-inertial regime.

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Gravity modes in rapidly rotating stars

Cited by 81 publications

References 30 publications

Coupling between internal waves and shear-induced turbulence in stellar radiation zones: the critical layers

Coupling between internal waves and shear-induced turbulence in stellar radiation zones: the critical layers

Seismic modelling of the late Be stars HD 181231 and HD 175869 observed with CoRoT: a laboratory for mixing processes

High-precision CoRoT space photometry and fundamental parameter determination of the B2.5V star HD 48977

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