J/A+A/621/A21 Activity of Kepler stars (Reinhold+, 2019)
Transition from spot to faculae domination.
An alternate explanation for the dearth of intermediate Kepler rotation periods.
Reinhold T., Bell K.J., Kuszlewicz J., Hekker S., Shapiro A.I.
<Astron. Astrophys. 621, A21 (2019)>
=2019A&A...621A..21R 2019A&A...621A..21R (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable
Keywords: stars: activity - stars: rotation
Abstract:
The study of stellar activity cycles is crucial to understand the
underlying dynamo and how it causes magnetic activity signatures such
as dark spots and bright faculae. Having knowledge about the dominant
source of surface activity might allow us to draw conclusions about
the stellar age and magnetic field topology, and to put the solar
cycle in context.
We investigate the underlying process that causes magnetic activity by
studying the appearance of activity signatures in contemporaneous
photometric and chromospheric time series.
Lomb-Scargle periodograms are used to search for cycle periods present
in the photometric and chromospheric time series. To emphasize the
signature of the activity cycle we account for rotation-induced
scatter in both data sets by fitting a quasi-periodic Gaussian process
model to each observing season. After subtracting the rotational
variability, cycle amplitudes and the phase difference between the two
time series are obtained by fitting both time series simultaneously
using the same cycle period.
We find cycle periods in 27 of the 30 stars in our sample. The phase
difference between the two time series reveals that the variability in
fast-rotating active stars is usually in anti-phase, while the
variability of slowly rotating inactive stars is in phase. The
photometric cycle amplitudes are on average six times larger for the
active stars. The phase and amplitude information demonstrates that
active stars are dominated by dark spots, whereas less-active stars
are dominated by bright faculae. We find the transition from spot to
faculae domination to be at the Vaughan-Preston gap, and around a
Rossby number equal to one.
We conclude that faculae are the dominant ingredient of stellar
activity cycles at ages ≳2.55Gyr. The data further suggest that the
Vaughan-Preston gap cannot explain the previously detected dearth of
Kepler rotation periods between 15 and 25 days. Nevertheless, our
results led us to propose an explanation for the lack of rotation
periods to be due to the non-detection of periodicity caused by the
cancelation of dark spots and bright faculae at ∼800Myr.
Description:
In the current study, data from three different sources have been
used. Long-term V band and Stroemgren b and y photometric
time series have successfully been requested from Messina &
Guinan (2002A&A...393..225M 2002A&A...393..225M, Cat. J/A+A/393/225) and Lockwood et al.
(2007ApJS..171..260L 2007ApJS..171..260L), respectively. For all stars, chromospheric
emission data from the Mount Wilson survey are publicly available
(ftp://solis.nso.edu/MountWilson_HK).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 135 30 Basic stellar parameters of the sample taken
from Simbad
tableb1.dat 106 30 Physical parameters of the sample
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See also:
J/ApJ/457/L99 : 25yr CaII-HK observations of F-K nearby stars (Baliunas+, 1996)
J/A+A/393/225 : Starspot cycles of six young solar analogues (Messina+, 2002)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- HD HD number
9- 18 A10 --- Name Name
20- 22 A3 --- Type Object type (1)
24- 30 A7 --- SpType Spectral type (2)
32- 35 I4 K Teff Effective temperature
37- 39 I3 K E_Teff Error on Teff (upper value)
41- 43 I3 K e_Teff Error on Teff (lower value)
45- 48 F4.2 [cm/s2] logg Surface gravity
50- 53 F4.2 [cm/s2] E_logg Error on logg (upper value)
55- 58 F4.2 [cm/s2] e_logg Error on logg (lower value)
60- 64 F5.2 [-] [Fe/H] Metallicity
66- 69 F4.2 [-] E_[Fe/H] Error on [Fe/H] (upper value)
71- 74 F4.2 [-] e_[Fe/H] Error on [Fe/H] (lower value)
76-135 A60 --- Ref References
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Note (1): The object type reads as follows:
BY* = Variable of BY Dra type
RS* = Variable of RS CVn type
PM* = High proper-motion star
SB* = Spectroscopic binary
** = Double or multiple star
Fl* = Flare star
Note (2): Spectral types have been adopted from Messina & Guinan
(2002A&A...393..225M 2002A&A...393..225M, Cat. J/A+A/393/225) and Lockwood et al.
(2007ApJS..171..260L 2007ApJS..171..260L).
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Byte-by-byte Description of file: tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- HD HD number
9- 12 F4.2 mag B-V B-V colour index (1)
14- 19 F6.3 [-] logR'HK Activity index (1)
21- 25 F5.2 d Prot Rotation period (2)
27- 31 F5.2 yr Pcyc ?=- Cycle period (3)
33- 36 F4.2 yr e_Pcyc ?=- rms uncertainty on Pcyc
38- 42 F5.1 yr Plcp ?=- Possible long period subtracted from the
photometric time series
44- 48 F5.1 yr Plcc ?=- Possible long periods subtracted from the
chromospheric time series
50- 54 F5.2 mmag Ampp ? Amplitude to the photometric time series
56- 59 F4.2 mmag e_Ampp ? rms uncertainty on Ampp
61- 65 F5.2 mmag Ampc ? Amplitude to the chromospheric time series
67- 70 F4.2 mmag e_Ampc ? rms uncertainty on Ampc
72- 76 F5.2 --- Dphi ?=- Phase difference between the
two time series
78- 81 F4.2 --- e_Dphi ?=- rms uncertainty on Dphi
83- 85 A3 --- Flagp Photometric flag (4)
87- 89 A3 --- Flagc Chromospheric flag (4)
91- 94 F4.2 --- chi2p ?=- Photometric time series chi2 value
96-100 F5.2 --- chi2c ?=- Chromospheric time series chi2 value
102-106 F5.2 --- chi2s ?=- Combined time series chi2 value
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Note (1): adopted from Lockwood et al. (2007ApJS..171..260L 2007ApJS..171..260L) and
Baliunas et al. (1996ApJ...457L..99B 1996ApJ...457L..99B, Cat. J/ApJ/457/L99).
Note (2): Rotation periods have been taken from Baliunas et al.
(1996ApJ...457L..99B 1996ApJ...457L..99B, Cat. J/ApJ/457/L99 and Messina & Guinan
(2002A&A...393..225M 2002A&A...393..225M, Cat. J/A+A/393/225).
Note (3): Cycle periods are the best sine fit periods to both data sets
simultaneously.
Note (4): The values for Flagp and Flagc provide quality flags for the goodness
of the periodicity in the respective time series.
The values represent the following:
1 = weak periodicity
2 = moderate to good periodicity
3 = excellent periodicity
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 18-Dec-2018