Non-radial oscillation modes with long lifetimes in giant stars

Ridder, J. De; Barban, C.; Baudin, F.; Carrier, F.; Hatzes, A. P.; Hekker, S.; Kallinger, T.; Weiß, W. W.; Baglin, A.; Auvergne, M.; Samadi, R.; Barge, P.; Deleuil, M.

doi:10.1038/nature08022

Cited by 283 publications

(268 citation statements)

References 20 publications

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“…An important new tool comes from mixed modes that were recently identified in red giants 3,4 . Stochastically excited solar-like oscillations in evolved G and K giant stars 8 have been well studied in terms of theory [9][10][11][12] , and the main results are consistent with recent observations from space-based photometry 13,14 . Whereas pressure modes are completely trapped in the outer acoustic cavity, mixed modes also probe the central regions and carry additional information from the core region, which is probed by gravity modes.…”

supporting

confidence: 81%

Fast core rotation in red-giant stars as revealed by gravity-dominated mixed modes

Beck

Montalbán

Kallinger

et al. 2011

Nature

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486

544

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When the core hydrogen is exhausted during stellar evolution, the central region of a star contracts and the outer envelope expands and cools, giving rise to a red giant. Convection takes place over much of the star's radius. Conservation of angular momentum requires that the cores of these stars rotate faster than their envelopes; indirect evidence supports this 1,2 . Information about the angular-momentum distribution is inaccessible to direct observations, but it can be extracted from the effect of rotation on oscillation modes that probe the stellar interior. Here we report an increasing rotation rate from the surface of the star to the stellar core in the interiors of red giants, obtained using the rotational frequency splitting of recently detected 'mixed modes' 3,4 . By comparison with theoretical stellar models, we conclude that the core must rotate at least ten times faster than the surface. This observational result confirms the theoretical prediction of a steep gradient in the rotation profile towards the deep stellar interior 1,5,6 .The asteroseismic approach to studying stellar interiors exploits information from oscillation modes of different radial order n and angular degree l, which propagate in cavities extending at different depths 7 . Stellar rotation lifts the degeneracy of non-radial modes, producing a multiplet of (2l 1 1) frequency peaks in the power spectrum for each mode. The frequency separation between two mode components of a multiplet is related to the angular velocity and to the properties of the mode in its propagation region. More information on the exploitation of rotational splitting of modes may be found in the Supplementary Information. An important new tool comes from mixed modes that were recently identified in red giants 3,4 . Stochastically excited solar-like oscillations in evolved G and K giant stars 8 have been well studied in terms of theory [9][10][11][12] , and the main results are consistent with recent observations from space-based photometry 13,14 . Whereas pressure modes are completely trapped in the outer acoustic cavity, mixed modes also probe the central regions and carry additional information from the core region, which is probed by gravity modes. Mixed dipole modes (l 5 1) appear in the Fourier power spectrum as dense clusters of modes around those that are best trapped in the acoustic cavity. These clusters, the components of which contain varying amounts of influence from pressure and gravity modes, are referred to as 'dipole forests'.We present the Fourier spectra of the brightness variations of stars KIC 8366239 (Fig. 1a), KIC 5356201 ( Supplementary Fig. 3a) and KIC 12008916 ( Supplementary Fig. 5a), derived from observations with the Kepler spacecraft. The three spectra show split modes, the spherical degree of which we identify as l 5 1. These detected multiplets cannot have been caused by finite mode lifetime effects from mode damping, because that would not lead to a consistent multiplet appearance over several orders such as that shown in Fig. 1. ...

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supporting

confidence: 81%

Fast core rotation in red-giant stars as revealed by gravity-dominated mixed modes

Beck

Montalbán

Kallinger

et al. 2011

Nature

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486

544

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“…Solar-like oscillations have now been firmly detected in several red giant stars, from both Doppler velocity measurements (see the review by Bedding & Kjeldsen 2006) as well as from space based photometry measurements (Barban et al 2007;de Ridder et al 2006). More recently, detection of solar-like oscillations by CoRoT in a huge number of red giant stars has been announced by de Ridder et al (2009). Why look at solar-like oscillations in red giant stars?…”

Section: Discussion and Perspectivesmentioning

confidence: 99%

Stochastic Excitation of Acoustic Modes in Stars

Samadi

2011

The Pulsations of the Sun and the Stars

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Abstract. For more than ten years, solar-like oscillations have been detected and frequencies measured for a growing number of stars with various characteristics (e.g. different evolutionary stages, effective temperatures, gravities, metal abundances ...).Excitation of such oscillations is attributed to turbulent convection and takes place in the uppermost part of the convective envelope. Since the pioneering work of Goldreich & Keely (1977), more sophisticated theoretical models of stochastic excitation were developed, which differ from each other both by the way turbulent convection is modelled and by the assumed sources of excitation. We review here these different models and their underlying approximations and assumptions.We emphasize how the computed mode excitation rates crucially depend on the way turbulent convection is described but also on the stratification and the metal abundance of the upper layers of the star. In turn we will show how the seismic measurements collected so far allow us to infer properties of turbulent convection in stars.

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“…De Ridder et al 2009. CoRoT continues to produce excellent results on red giants, main-sequence and subgiant stars.…”

Section: Solar-like Oscillationsmentioning

confidence: 99%

Commission 27: Variable Stars

Kawaler¹,

Handler²,

Aerts³

et al. 2008

Proc. IAU

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The Organizing Committee of Commission 27 has decided to again provide a somewhat abbreviated bibliography as part of this triennial report, as astronomy-centered search engines and on-line publications continue to blossom. We focus on selected highlights in variable star research over the past three years. Further results can be found in numerous proceedings of conferences held in the time frame covered by this report.

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Non-radial oscillation modes with long lifetimes in giant stars

Cited by 283 publications

References 20 publications

Fast core rotation in red-giant stars as revealed by gravity-dominated mixed modes

Fast core rotation in red-giant stars as revealed by gravity-dominated mixed modes

Stochastic Excitation of Acoustic Modes in Stars

Commission 27: Variable Stars

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