J/A+A/603/A52 Activity cycles in 3203 Kepler stars (Reinhold+, 2017)
Evidence for photometric activity cycles in 3203 Kepler stars.
Reinhold T., Cameron R.H., Gizon L.
<Astron. Astrophys. 603, A52 (2017)>
=2017A&A...603A..52R 2017A&A...603A..52R (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Photometry
Keywords: Sun: activity - stars: activity - starspots - stars: rotation -
techniques: photometric
Abstract:
In recent years it has been claimed that the length of stellar
activity cycles is determined by the stellar rotation rate. It has
been observed that the cycle period increases with rotation period
along two distinct sequences, known as the active and inactive
sequences. In this picture the Sun occupies a solitary position
between the two sequences. Whether the Sun might undergo a
transitional evolutionary stage is currently under debate. Our goal is
to measure cyclic variations of the stellar light curve amplitude and
the rotation period using four years of Kepler data. Periodic changes
in the light curve amplitude or the stellar rotation period are
associated with an underlying activity cycle. Using a recent sample of
active stars we compute the rotation period and the variability
amplitude for each individual Kepler quarter and search for periodic
variations of both time series. To test for periodicity in each
stellar time series we consider Lomb-Scargle periodograms and use a
selection based on a false alarm probability (FAP). We detect
amplitude periodicities in 3203 stars between 0.5-6 years covering
rotation periods between 1-40 days. Given our sample size of 23,601
stars and our selection criteria that the FAP is less than 5%, this
number is almost three times higher than that expected from pure
noise. We do not detect periodicities in the rotation period beyond
those expected from noise. Our measurements reveal that the cycle
period shows a weak dependence on rotation rate, slightly increasing
for longer rotation periods. We further show that the shape of the
variability deviates from a pure sine curve, consistent with
observations of the solar cycle. The cycle shape does not show a
statistically significant dependence on effective temperature. We
detect activity cycles in more than 13% of our final sample with a FAP
of 5% (calculated by randomly shuffling the measured 90-day
variability measurements for each star). Our measurements do not
support the existence of distinct sequences in the Prot-Pcyc plane,
although there is some evidence for the inactive sequence for rotation
periods between 5-25 days. Unfortunately,the total observing time is
too short to draw sound conclusions on activity cycles with similar
lengths to that of the solar cycle.
Description:
Rvar time series, sine fit parameters, mean rotation periods, and
false alarm probabilities of all 3203 Kepler stars are presented. For
simplicity, the KIC number and the fit parameters of a certain star
are repeated in each line. The fit function to the Rvar(t) time series
equals y_fit=Acyc*sin(2*pi/(Pcyc*365)*(t-t0))+Offset.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 33 3203 List of studied stars
rvar.dat 57 49991 Rvar time series and fit parameters
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 8 I8 --- KIC Unique Kepler input catalog number
10- 19 F10.6 deg RAdeg KIC right ascension (J2000)
21- 30 F10.6 deg DEdeg KIC declination (J2000)
32- 33 I2 --- Nmeas Number of measurements in rvar.dat table
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Byte-by-byte Description of file: rvar.dat
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Bytes Format Units Label Explanations
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1- 8 I8 - KIC Unique Kepler input catalog number
10- 16 F7.2 d t Midpoints of the quarters: t=BJD-2454833
18- 22 F5.2 % Rvar Variability range
24- 27 F4.2 yr Pcyc Cycle period
29- 32 F4.2 % Acyc Cycle amplitude
34- 40 F7.2 d t0 Phase t0=BJD-2454833
42- 46 F5.2 % Offset Offset of sine fit, i.e., mean activity level
48- 52 F5.2 d Prot Mean rotation period
54- 57 F4.2 % FAP False alarm probability
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Acknowledgements:
Timo Reinhold, reinhold(at)mps.mpg.de
(End) T. Reinhold [MPS Goettingen, Germany], P. Vannier [CDS] 31-May-2017