J/A+A/626/A121 Buoyancy radius of γ Dor stars (Ouazzani+, 2019)
γ Doradus stars as test of angular momentum transport models.
Ouazzani R.-M., Marques J.P., Goupil M-J., Christophe S., Antoci V.,
Salmon S.J.A.J., Ballot J.
<Astron. Astrophys. 626, A121 (2019)>
=2019A&A...626A.121O 2019A&A...626A.121O (SIMBAD/NED BibCode)
ADC_Keywords: Asteroseismology ; Stars, variable
Keywords: stars: evolution - stars: low-mass - stars: oscillations -
stars: rotation - stars: statistics - asteroseismology
Abstract:
Helioseismology and asteroseismology of red giant stars have shown
that distribution of angular momentum in stellar interiors, and the
evolution of this distribution with time remains an open issue in
stellar physics. Owing to the unprecedented quality and long baseline
of Kepler photometry, we are able to seismically infer internal
rotation rates in γ Doradus stars, which provide the
main-sequence counterpart to the red-giants puzzle. Here, we confront
these internal rotation rates to stellar evolution models which
account for rotationally induced transport of angular momentum, in
order to test angular momentum transport mechanisms. On the one hand,
we used a stellar model-independent method developed by our team in
order to obtain accurate, seismically inferred, buoyancy radii and
near-core rotation for 37 γ Doradus stars observed by Kepler. We
show that the stellar buoyancy radius can be used as a reliable
evolution indicator for field stars on the main sequence. On the other
hand, we computed rotating evolutionary models of intermediate-mass
stars including internal transport of angular momentum in radiative
zones, following the formalism developed in the series of papers
started by Zahn (1992A&A...265..115Z 1992A&A...265..115Z), with the cestam code. This code
calculates the rotational history of stars from the birth line to the
tip of the RGB. The initial angular momentum content has to be set
initially, which is done here by fitting rotation periods in young
stellar clusters. We show a clear disagreement between the near-core
rotation rates measured in the sample and the rotation rates obtained
from the evolutionary models including rotationally induced transport
of angular momentum following Zahn's prescriptions. These results
show a disagreement similar to that of the Sun and red giant stars in
the considered mass range. This suggests the existence of missing
mechanisms responsible for the braking of the core before and along
the main sequence. The efficiency of the missing mechanisms is
investigated. The transport of angular momentum as formalized by Zahn
and Maeder cannot explain the measurements of near-core rotation in
main-sequence intermediate-mass stars we have at hand.
Description:
We compare measurements for Kepler observations of γ Doradus
stars obtained using Christophe et al. (2018A&A...618A..47C 2018A&A...618A..47C) to the
evolutionary models including angular momentum transport as described
in Sect.2 in a near-core rotation versus buoyancy radius plane. The
results are given in Fig. 7 of the paper. We compared rotational
evolution on the main sequence for a typical mass of γ Dor
stars: 1.6M☉, each time considering two metallicities:
[M/H]=-0.06 and [M/H]=+0.28. The evolutionary models account for
transport of angular momentum via different prescriptions/mechanisms:
This corresponds to the files :
"evolRot-vs-BRm1.6z0.0114DL3-2.4_Z92.dat" and
"evolRot-vs-BRm1.6z0.0234DL5-7.2_Z92.dat".
* meridional circulation and shear-induced turbulence according to the
formalism of Z92, with overshooting of alphaov=0.15.
Files:
"evolRot-vs-BRm1.6z0.0234DL5-7.2_ov0.15.dat" and
"evolRot-vs-BRm1.6z0.0114DL3-2.4_ov0.15.dat".
* meridional circulation and shear-induced turbulence according to the
formalism of Z92, with enhanced horizontal viscosity (multiplied by a
factor a hundred compared to the first case).
Files:
"evolRot-vs-BRm1.6z0.0234DL5-7.2_Dhx100.dat", and
"evolRot-vs-BRm1.6z0.0114DL3-2.4_Dhx100.dat".
* meridional circulation and shear-induced turbulence according to the
formalism of Z92, with additional vertical viscosity (of
Nuv,add=1x108cm2/s).
Files:
"evolRot-vs-BRm1.6z0.0234DL5-7.2_Dv1d8.dat" and
"evolRot-vs-BRm1.6z0.0234DL5-7.2_Dv1d8.dat".
* solid body enforced along evolution:
"evolRot-vs-BRm1.6z0.0234DL5-7.2_SB.dat" and
"evolRot-vs-BRm1.6z0.0234DL5-7.2_SB.dat".
Finally, the file "obs.dat" gives the measurements of
buoyancy radii and near-core rotation frequencies obtained by the
method of Christophe et al. (2018A&A...618A..47C 2018A&A...618A..47C) for a sample of 37
γ Dor stars observed by the Kepler nominal mission.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
obs.dat 60 37 Buoyancy radii and near-core rotation frequencies
for 37 γ Dors observed by Kepler
list.dat 202 10 List of files files buoyancy radii and
near-core rotation frequency
files/* . 10 All buoyancy radii and near-core rotation
frequency results
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Byte-by-byte Description of file: obs.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
5- 12 I8 --- KIC KIC number
16- 24 F9.4 s BR Buoyancy radius
28- 36 F9.4 s e_BR Uncertainty on buoyancy radius
42- 48 F7.4 uHz Nurot Near-core rotation frequency
55- 60 F6.4 uHz e_Nurot Uncertainty on near-core rotation frequency
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Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 31 A31 --- FileName Name of the file with buoyancy radii and
near-core rotation frequency
in subdirectory files
33-202 A170 --- Com Model informations
--------------------------------------------------------------------------------
Byte-by-byte Description of file:files/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
4- 22 E19.13 s BR Buoyancy radius
26- 44 E19.13 uHz Nurot Near-core rotation frequency
--------------------------------------------------------------------------------
Acknowledgements:
Rhita M. Ouazzani, Rhita-Maria.Ouazzani(at)obspm.fr
(End) Patricia Vannier [CDS] 11-Apr-2019