J/A+A/574/A17 Period spacings in gamma Dor stars (Van Reeth+, 2015)
Detecting non-uniform period spacings in the Kepler photometry of gamma Doradus
stars: methodology and case studies.
Van Reeth T., Tkachenko A., Aerts C., Papics P. I., Degroote P.,
Debosscher J., Zwintz K., Bloemen S., De Smedt K., Hrudkova M.,
Raskin G., Van Winckel H.
<Astron. Astrophys. 574, A17 (2015)>
=2015A&A...574A..17V 2015A&A...574A..17V
ADC_Keywords: Models, evolutionary ; Stars, F-type ; Stars, variable
Keywords: asteroseismology - methods: data analysis -
stars: fundamental parameters - stars: variables: general
Abstract:
The analysis of stellar oscillations is one of the most reliable ways
to probe stellar interiors. Recent space missions such as Kepler have
provided us with an opportunity to study these oscillations with
unprecedented detail. For many multi-periodic pulsators such as gamma
Doradus stars, this led to the detection of dozens to hundreds of
oscillation frequencies that could not be found from ground-based
observations.
We aim to detect non-uniform period spacings in the Fourier spectra of
a sample of gamma Doradus stars observed by Kepler. Such detection is
complicated by both the large number of significant frequencies in the
space photometry and by overlapping non-equidistant rotationally split
multiplets.
Guided by theoretical properties of gravity-mode oscillation of gamma
Doradus stars, we developed a period-spacing detection method and
applied it to Kepler observations of a few stars, after having tested
the performance from simulations.
The application of the technique resulted in the clear detection of
non-uniform period spacing series for three out of the five treated
Kepler targets. Disadvantages of the technique are also discussed, and
include the disability to distinguish between different values of the
spherical degree and azimuthal order of the oscillation modes, without
additional theoretical modelling.
Despite the shortcomings, the method is shown to enable solid
detections of period spacings for gamma Doradus stars, which will
allow future asteroseismic analyses of these stars.
Description:
In Section 4.1 of the paper, we illustrate the proposed methodology by
applying it on a simulated normalized light curve. The oscillation
frequencies which we used as input were computed by means of the MESA
stellar evolution code (Paxton et al. 2011ApJS..192....3P 2011ApJS..192....3P,
2013ApJS..208....4P 2013ApJS..208....4P) and the GYRE stellar oscillation code (Townsend &
Teitler, 2013MNRAS.435.3406T 2013MNRAS.435.3406T). The models were computed for a
1.6M☉ star at different phases of its evolution. We used the
standard MESA input physics with the Schwarzschild criterion for
convection and an overshoot value of 0.014 local pressure scale
heights in the formulation by Herwig (2000). The oscillation
frequencies were then shifted for a rotation velocity of 73km/s, using
the approximation by Chlebowski (1978AcA....28..441C 1978AcA....28..441C).
The computed input frequencies are listed in the data file described
below, together with the corresponding values for the spherical degree
l and the azimuthal order m.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 29 184 Oscillation frequencies used in the simulated
light curve in Section 4.1
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 24 E24.18 d-1 Freq [0.07/4.27] Input frequency value
26 I1 --- l [1/2] Spherical degree l
28- 29 I2 --- m [-2/2] Azimuthal order m
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Acknowledgements:
Timothy Van Reeth, timothy.vanreeth(at)ster.kuleuven.be
(End) Timothy Van Reeth [IvS,Leuven], Patricia Vannier [CDS] 28-Oct-2014