SOLAR-LIKE OSCILLATIONS IN LOW-LUMINOSITY RED GIANTS: FIRST RESULTS FROM
                    <i>KEPLER</i>

Bedding, Timothy R.; Huber, Daniel; Stello, Dennis; Elsworth, Y.; Hekker, S.; Kallinger, T.; Mathur, S.; Mosser, B.; Preston, H. L.; Ballot, J.; Barban, C.; Broomhall, Anne Marie; Buzasi, Derek L.; Chaplin, W. J.; García, Rafael A.; Gruberbauer, M.; Hale, Steven J.; Ridder, J. De; Frandsen, S.; Borucki, W. J.; Brown, T. M.; Christensen‐Dalsgaard, J.; Gilliland, Ronald L.; Jenkins, Jon M.; Kjeldsen, H.; Koch, David; Belkacem, K.; Bildsten, Lars; Bruntt, H.; Campante, Tiago L.; Deheuvels, S.; Derekas, A.; Dupret, Marc‐Antoine; Goupil, M. J.; Hatzes, A. P.; Houdek, G.; Ireland, Michael; Jiang, Chen; Karoff, C.; Kiss, L. L.; Lebreton, Y.; Miglio, A.; Montalbán, J.; Noels, A.; Roxburgh, I. W.; Sangaralingam, Vinothini; Stevens, I. R.; Suran, M. D.; Tarrant, N. J.; Weiß, Achim

doi:10.1088/2041-8205/713/2/l176

Cited by 225 publications

(181 citation statements)

References 47 publications

(65 reference statements)

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“…Claims of non-rigid rotation in white dwarfs have also been discussed 21 . The low-luminosity red giants 22 discussed here are in the early phase of hydrogen-shell burning, and have a core-to-envelope rotation rate more than twice as high as those of the massive stars 19,20 . When these stars enter the subsequent phase of core-helium burning, we believe that the core will undergo a slight expansion and the envelope will shrink, leading to a surface rotation on the horizontal branch larger than that on the red-giant branch 1 .…”

Section: Research Lettermentioning

confidence: 95%

“…The mean period spacing DPobs and its standard deviation were derived from the central multiplet components of the dipole modes. These three stars are classified as low-luminosity red-giant stars 22 . The observationally derived mean period spacing of the mixed modes indicates that they are in an early phase of red-giant evolution 4 , in which they are burning hydrogen in a shell around the helium core.…”

Section: Research Lettermentioning

confidence: 99%

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

Beck

Montalbán

Kallinger

et al. 2011

Nature

485

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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Section: Research Lettermentioning

confidence: 95%

Section: Research Lettermentioning

confidence: 99%

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

Beck

Montalbán

Kallinger

et al. 2011

Nature

485

544

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“…Theoretical calculations for the C-D diagram have been carried out for main-sequence stars (e.g., Monteiro et al 2002;Otí Floranes et al 2005;Mazumdar 2005;Gai et al 2009;White et al 2011) but prior to Kepler, observations were only available for a small number of stars. An observational C-D diagram has now been produced for red giants using Kepler observations (Bedding et al 2010a;Huber et al 2010). In this Letter we present an observational C-D diagram for main-sequence and subgiant stars.…”

Section: Asteroseismic Parametersmentioning

confidence: 98%

ASTEROSEISMIC DIAGRAMS FROM A SURVEY OF SOLAR-LIKE OSCILLATIONS WITH KEPLER

White

Bedding

Stello

et al. 2011

ApJ

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Photometric observations made by the NASA Kepler Mission have led to a dramatic increase in the number of mainsequence and subgiant stars with detected solar-like oscillations. We present an ensemble asteroseismic analysis of 76 solar-type stars. Using frequencies determined from the Kepler time-series photometry, we have measured three asteroseismic parameters that characterize the oscillations: the large frequency separation (Δν), the small frequency separation between modes of l = 0 and l = 2 (δν 02 ), and the dimensionless offset ( ). These measurements allow us to construct asteroseismic diagrams, namely the so-called Christensen-Dalsgaard diagram of δν 02 versus Δν, and the recently re-introduced diagram. We compare the Kepler results with previously observed solar-type stars and with theoretical models. The positions of stars in these diagrams places constraints on their masses and ages. Additionally, we confirm the observational relationship between and T eff that allows for the unambiguous determination of radial order and should help resolve the problem of mode identification in F stars.

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“…The observed oscillation spectra are indeed remarkably Sun-like, with a broad range of radial and nonradial modes in a characteristic comb pattern [7][8][9][10][11] …”

mentioning

confidence: 99%

Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars

Bedding

Mosser

Huber

et al. 2011

Nature

571

622

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Red giants are evolved stars that have exhausted the supply of hydrogen in their cores and instead burn hydrogen in a surrounding shell 1,2 . Once a red giant is sufficiently evolved, the helium in the core also undergoes fusion 3 . Outstanding issues in our understanding of red giants include uncertainties in the amount of mass lost at the surface before helium ignition and the amount of internal mixing from rotation and other processes 4 . Progress is hampered by our inability to distinguish between red giants burning helium in the core and those still only burning hydrogen in a shell. Asteroseismology offers a way forward, being a powerful tool for probing the internal structures of stars using their natural oscillation frequencies 5 . Here we report observations of gravity-mode period spacings in red giants 6 that permit a distinction between evolutionary stages to be made. We use high-precision photometry obtained by the Kepler spacecraft over more than a year to measure oscillations in several hundred red giants. We find many stars whose dipole modes show sequences with approximately regular period spacings. These stars fall into two clear groups, allowing us to distinguish unambiguously between hydrogen-shell-burning stars (period spacing mostly 50 seconds) and those that are also burning helium (period spacing 100 to 300 seconds).Oscillations in red giants, like those in the Sun, are thought to be excited by near-surface convection. The observed oscillation spectra are indeed remarkably Sun-like, with a broad range of radial and nonradial modes in a characteristic comb pattern [7][8][9][10][11]

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SOLAR-LIKE OSCILLATIONS IN LOW-LUMINOSITY RED GIANTS: FIRST RESULTS FROM KEPLER

Cited by 225 publications

References 47 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

ASTEROSEISMIC DIAGRAMS FROM A SURVEY OF SOLAR-LIKE OSCILLATIONS WITH KEPLER

Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars

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