J/A+A/616/A24 Rotation in RGBs from Kepler asteroseismology (Gehan+, 2018)
Core rotation braking on the red giant branch for various mass ranges.
Gehan C., Mosser B., Michel E., Samadi R., Kallinger T.
<Astron. Astrophys. 616, A24 (2018)>
=2018A&A...616A..24G 2018A&A...616A..24G (SIMBAD/NED BibCode)
ADC_Keywords: Asteroseismology ; Stars, giant
Keywords: asteroseismology - methods: data analysis - stars: interiors -
stars: oscillations - stars: rotation - stars: solar-type
Abstract:
Asteroseismology allows us to probe stellar interiors. In the case of
red giant stars, conditions in the stellar interior are such as to
allow for the existence of mixed modes, consisting in a coupling
between gravity waves in the radiative interior and pressure waves in
the convective envelope. Mixed modes can thus be used to probe the
physical conditions in red giant cores. However, we still need to
identify the physical mechanisms that transport angular momentum
inside red giants, leading to the slow-down observed for red giant
core rotation. Thus large-scale measurements of red giant core
rotation are of prime importance to obtain tighter constraints on the
efficiency of the internal angular momentum transport, and to study
how this efficiency changes with stellar parameters.
This work aims at identifying the components of the rotational
multiplets for dipole mixed modes in a large number of red giant
oscillation spectra observed by Kepler. Such identification provides
us with a direct measurement of the red giant mean core rotation.
We compute stretched spectra that mimic the regular pattern of pure
dipole gravity modes. Mixed modes with the same azimuthal order are
expected to be almost equally spaced in stretched period, with a
spacing equal to the pure dipole gravity mode period spacing. The
departure from this regular pattern allows us to disentangle the
various rotational components and therefore to determine the mean core
rotation rates of red giants.
We automatically identify the rotational multiplet components of 1183
stars on the red giant branch with a success rate of 69 per cent with
respect to our initial sample. As no information on the internal
rotation can be deduced for stars seen pole-on, we obtain mean core
rotation measurements for 875 red giant branch stars. This large
sample includes stars with a mass as large as 2.5 solar masses,
allowing us to test the dependence of the core slow-down rate on the
stellar mass.
Disentangling rotational splittings from mixed modes is now possible
in an automated way for stars on the red giant branch, even for the
most complicated cases, where the rotational splittings exceed half
the mixed-mode spacing. This work on a large sample allows us to
refine previous measurements of the evolution of the mean core
rotation on the red giant branch. Rather than a slight slow-down, our
results suggest rotation is constant along the red giant branch, with
values independent of the mass.
Description:
Seismic global parameters, mean core rotational splitting and number
of rotational components in the oscillation spectrum of the stars
analysed in the paper. Each star is identified with its KIC number
(Kepler Input Catalog, Cat. V/133).
Rotational splittings of gravity-dominated mixed modes were measured
for for hundreds of red giant branch stars. Zero rotational splitting
values correspond to stars nearby pole-on, where only one rotation
component is visible and no measurement of the mean core rotational
splitting is possible. Evolutionary stages are identified from Vrard
et al. (2016, Cat. J/A+A/588/A87). The period spacings measured by
Vrard et al. (2016, Cat. J/A+A/588/A87) were used as first estimates
and refined in this paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
rotation.dat 43 1140 Seismic global parameters and rotational splittings
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
J/A+A/540/A143 : Oscillations of red giants observed by Kepler (Mosser+, 2012)
J/A+A/588/A87 : Seismic global parameters of 6111 KIC (Vrard+, 2016)
Byte-by-byte Description of file: rotation.dat
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Bytes Format Units Label Explanations
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1- 9 I9 --- KIC KIC number
11- 15 F5.2 muHz Dnu Large separation
17- 22 F6.2 muHz numax Frequency of maximum oscillation power
24- 29 F6.2 s DPi1 Period spacing
31- 35 F5.1 nHz dnurot Rotational splitting
37- 41 F5.2 nHz e_dnurot Uncertainty on dnurot
43 I1 --- Ncomp Number of rotational components
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Acknowledgements:
Charlotte Gehan, charlotte.gehan(at)obspm.fr
References:
Mosser et al., Paper I 2015A&A...584A..50M 2015A&A...584A..50M
Vrad et al., Paper II 2016A&A...588A..87V 2016A&A...588A..87V, Cat. J/A+A/588/A87
(End) Charlotte Gehan [PSL/Paris Obs.], Patricia Vannier [CDS] 30-Aug-2018