Theoretical power spectra of mixed modes in low-mass red giant stars

Grosjean, M.; Dupret, Marc‐Antoine; Belkacem, K.; Montalbán, J.; Samadi, R.; Mosser, B.

doi:10.1051/0004-6361/201423827

Cited by 68 publications

(97 citation statements)

References 71 publications

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“…Further confirmation of the evolutionary state is derived from a comparison of the oscillation spectrum of HD 181907 with spectra of Kepler red giants with similar large separations and ν max values, and with identified evolutionary stages (Mosser et al 2014). In that respect, the spectrum of HD 181907 looks like a red-clump star spectrum, with significant power in the gravity-dominated mixed modes (Grosjean et al 2014). We therefore believe this star to be a core-He-burning star, based on both spectrometric and asteroseismic arguments.…”

Section: Carbon Isotopic Ratiomentioning

confidence: 83%

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints

Lagarde

Miglio

Eggenberger

et al. 2015

A&A

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Context. The availability of asteroseismic constraints for a large sample of red giant stars from the CoRoT and Kepler missions paves the way for various statistical studies of the seismic properties of stellar populations. Aims. We use a detailed spectroscopic study of 19 CoRoT red giant stars to compare theoretical stellar evolution models to observations of the open cluster NGC 6633 and field stars. Methods. In order to explore the effects of rotation-induced mixing and thermohaline instability, we compare surface abundances of carbon isotopic ratio and lithium with stellar evolution predictions. These chemicals are sensitive to extra-mixing on the red giant branch. Results. We estimate mass, radius, and distance for each star using the seismic constraints. We note that the Hipparcos and seismic distances are different. However, the uncertainties are such that this may not be significant. Although the seismic distances for the cluster members are self consistent they are somewhat larger than the Hipparcos distance. This is an issue that should be considered elsewhere. Models including thermohaline instability and rotation-induced mixing, together with the seismically determined masses can explain the chemical properties of red giant targets. However, with this sample of stars we cannot perform stringent tests of the current stellar models. Tighter constraints on the physics of the models would require the measurement of the core and surface rotation rates, and of the period spacing of gravity-dominated mixed modes. A larger number of stars with longer times series, as provided by Kepler or expected with Plato, would help ensemble asteroseismology.

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Section: Carbon Isotopic Ratiomentioning

confidence: 83%

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints

Lagarde

Miglio

Eggenberger

et al. 2015

A&A

Self Cite

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“…In red giants, mixed modes are generally observable when the evanescent region separating the core and envelope is quite narrow, which occurs for RGB stars below the luminosity bump (Dupret et al 2009;Grosjean et al 2014). As stars evolve further up the RGB and expand, the evanescent region thickens, and mixed modes become undetectable.…”

Section: Red Clumpmentioning

confidence: 99%

Asteroseismic Signatures of Evolving Internal Stellar Magnetic Fields

Cantiello

Fuller

Bildsten

2016

ApJ

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Recent asteroseismic analyses indicate the presence of strong (B  10 5 G) magnetic fields in the cores of many red giant stars. Here, we examine the implications of these results for the evolution of stellar magnetic fields, and we make predictions for future observations. Those stars with suppressed dipole modes indicative of strong core fields should exhibit moderate but detectable quadrupole mode suppression. The long magnetic diffusion times within stellar cores ensure that dynamo-generated fields are confined to mass coordinates within the main-sequence (MS) convective core, and the observed sharp increase in dipole mode suppression rates above 1.5 M e is likely explained by the larger convective core masses and faster rotation of these more massive stars. In clump stars, core fields of ∼10 5 G can suppress dipole modes, whose visibility should be equal to or less than the visibility of suppressed modes in ascending red giants. High dipole mode suppression rates in low-mass (M  2 M e ) clump stars would indicate that magnetic fields generated during the MS can withstand subsequent convective phases and survive into the compact remnant phase. Finally, we discuss implications for observed magnetic fields in white dwarfs and neutron stars, as well as the effects of magnetic fields in various types of pulsating stars.

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“…We can thus detect l = 2 modes only when their frequencies are very close to those of pure p modes. Outside these frequency ranges, the l = 2 modes have inertias that are too large for the modes to have detectable heights in the oscillation spectra, even with the longest Kepler datasets (see, e.g., Grosjean et al 2014). This makes it much harder to precisely estimate the asymptotic properties of l = 2 pure g modes, which are required if we want to apply the method of Goupil et al (2013) to l = 2 modes.…”

Section: Preliminary Testmentioning

confidence: 99%

Near-degeneracy effects on the frequencies of rotationally-split mixed modes in red giants

Deheuvels

Ouazzani

Basu

2017

A&A

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Context. The Kepler space mission has made it possible to measure the rotational splittings of mixed modes in red giants, thereby providing an unprecedented opportunity to probe the internal rotation of these stars. Aims. Asymmetries have been detected in the rotational multiplets of several red giants. This is unexpected since all the red giants whose rotation profiles have been measured thus far are found to rotate slowly, and low rotation, in principle, produces symmetrical multiplets. Our aim here is to explain these asymmetries and find a way of exploiting them to probe the internal rotation of red giants. Methods. We show that in the cases where asymmetrical multiplets were detected, near-degeneracy effects are expected to occur, because of the combined effects of rotation and mode mixing. Such effects have not been taken into account so far. By using both perturbative and non-perturbative approaches, we show that near-degeneracy effects produce multiplet asymmetries that are very similar to the observations. We then propose and validate a method based on the perturbative approach to probe the internal rotation of red giants using multiplet asymmetries. Results. We successfully apply our method to the asymmetrical l = 2 multiplets of the Kepler young red giant KIC 7341231 and obtain precise estimates of its mean rotation in the core and the envelope. The observed asymmetries are reproduced with a good statistical agreement, which confirms that near-degeneracy effects are very likely the cause of the detected multiplet asymmetries. Conclusions. We expect near-degeneracy effects to be important for l = 2 mixed modes all along the red giant branch (RGB). For l = 1 modes, these effects can be neglected only at the base of the RGB. They must therefore be taken into account when interpreting rotational splittings and as shown here, they can bring valuable information about the internal rotation of red giants.

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Theoretical power spectra of mixed modes in low-mass red giant stars

Cited by 68 publications

References 71 publications

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints

Asteroseismic Signatures of Evolving Internal Stellar Magnetic Fields

Near-degeneracy effects on the frequencies of rotationally-split mixed modes in red giants

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