Probing the core structure and evolution of red giants using gravity-dominated mixed modes observed with Kepler

By B. Mosser, M. Goupil, K. Belkacem, E. Michel, D. Stello, J. Marques, Y. Elsworth, C. Barban, P. Beck, T. Bedding and 8 more. 2012

195 citations recorded by the source corpus.

Context. There are now more than 22 months of long-cadence data available for thousands of red giants observed with the Kepler space mission. Consequently, we are able to clearly resolve fine details in their oscillation spectra and see many components of the mixed modes that probe the stellar core. Aims. We report for the first time a parametric fit to the pattern of the � = 1 mixed modes in red giants, which is a powerful tool to identify gravity-dominated mixed modes. With these modes, which share the characteristics of pressure and gravity modes, we are able to probe directly the helium core and the surrounding shell where hydrogen is burning. Methods. We propose two ways for describing the so-called mode bumping that affects the frequencies of the mixed modes. Firstly, a phenomenological approach is used to describe the main features of the mode bumping. Alternatively, a quasi-asymptotic mixed-mode relation provides a powerful link between seismic observations and the stellar interior structure. We used period echelle diagrams to emphasize the detection of the gravity-dominated mixed modes. Results. The asymptotic relation for mixed modes is confirmed. It allows us to measure the gravity-mode period spacings in more than two hundred red giant stars. The identification of the gravity-dominated mixed modes allows us to complete the identification of all major peaks in a red giant oscillation spectrum, with significant consequences for the true identification of � = 3 modes, of � = 2 mixed modes, for the mode widths and amplitudes, and for the � = 1 rotational splittings. Conclusions. The accurate measurement of the gravity-mode period spacing provides an effective probe of the inner, g-mode cavity. The derived value of the coupling coefficient between the cavities is different for red giant branch and clump stars. This provides a probe of the hydrogen-shell burning region that surrounds the helium core. Core contraction as red giants ascend the red giant branch can be explored using the variation of the gravity-mode spacing as a function of the mean large separation.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/937ad952d5d93394599f052adfa81f89bebd9b19

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In Astronomy and Astrophysics

1. D. Huber
2. D. Stello
3. W. Chaplin
4. Jo Bovy
5. A. Miglio
6. Hans-Walter Rix
7. T. Bedding
8. B. Mosser

In Instrumentation

1. D. Huber
2. D. Stello
3. W. Chaplin
4. B. Mosser
5. T. Bedding
6. A. Miglio
7. Jo Bovy
8. Y. Elsworth

Citations in the corpus

• Asteroseismology of Solar-Type and Red-Giant Stars (2013, methodology): “…results have been obtained from peak-bagging (e.g., Baudin et al. 2011, Appourchaux et al. 2012) and from other techniques (Huber et al. 2011b, Mosser et al. 2012a) developed from ground-based analysis methods (e.g., Kjeldsen et al. 2008), including results on stars in open clusters (Stello…”
• The connection between stellar granulation and oscillation as seen by the Kepler mission (2014, background): “…analysis of an individual star (di Mauro et al. 2011) and of the radial (Kallinger et al. 2012) and non-radial mixed mode spectra (Bedding et al. 2011; Mosser et al. 2012c), and how the latter are used to constrain rotational properties (Beck et al. 2012) and their evolution (Mosser et al. 2012b).”
• Spin down of the core rotation in red giants (2012, methodology): “The model indicates that the coefficient η decreases towards unity when a star evolves along the RGB, due to the significant increase of the gravity radial orders605 (Mosser et al. 2012c).”
• ASTEROSEISMIC CLASSIFICATION OF STELLAR POPULATIONS AMONG 13,000 RED GIANTS OBSERVED BY KEPLER (2013, methodology): “A detailed study of the difference between the period spacing of uncoupled g-modes and that of the mixed modes was conducted by Mosser et al. (2012a).”
• ANGULAR MOMENTUM TRANSPORT WITHIN EVOLVED LOW-MASS STARS (2014, methodology): “In the era of space asteroseismology, the Kepler satellite enabled the measurement of the core rotation in many red giant branch (RGB) stars using the splitting of mixed modes (Beck et al. 2012; Deheuvels et al. 2012; Mosser et al. 2012b; Deheuvels et al. 2014).”
• Seismic diagnostics for transport of angular momentum in stars. I. Rotational splittings from the pre-main sequence to the red-giant branch. (2012, background): “Such rotation splittings lead to a core rotation rate that is closer to the observations but still too high by almost one order of magnitude compared with what is seen in recent observations (Beck et al. 2012; Deheuvels et al. 2012; Mosser et al. 2012a).”
• THE APOKASC CATALOG: AN ASTEROSEISMIC AND SPECTROSCOPIC JOINT SURVEY OF TARGETS IN THE KEPLER FIELDS (2014, background): “Rapid rotation in the cores of red giants has been discovered (Beck et al. 2012; Deheuvels et al. 2012; Mosser et al. 2012a).”
• Mixed modes in red giants: a window on stellar evolution (2014, methodology): “1) occupy a small region of the ΔΠ1-Δν diagram, around 300 s and 4.1μHz (Mosser et al. 2012b).”