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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 (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:
FileName Lrecl Records Explanations
ReadMe 80 . This file stars.dat 33 3203 List of studied stars rvar.dat 57 49991 Rvar time series and fit parameters
See also: V/133 : Kepler Input Catalog (Kepler Mission Team, 2009) Byte-by-byte Description of file: stars.dat
Bytes Format Units Label Explanations
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
Byte-by-byte Description of file: rvar.dat
Bytes Format Units Label Explanations
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
Acknowledgements: Timo Reinhold, reinhold(at)mps.mpg.de
(End) T. Reinhold [MPS Goettingen, Germany], P. Vannier [CDS] 31-May-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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