J/ApJS/209/5 Superflares of Kepler stars. I. (Shibayama+, 2013)
Superflares on solar-type stars observed with Kepler.
I. Statistical properties of superflares.
Shibayama T., Maehara H., Notsu S., Notsu Y., Nagao T., Honda S.,
Ishii T.T., Nogami D., Shibata K.
<Astrophys. J. Suppl. Ser., 209, 5 (2013)>
=2013ApJS..209....5S 2013ApJS..209....5S
ADC_Keywords: Stars, G-type ; Stars, variable ; Stars, flare
Keywords: stars: activity - stars: flare - stars: rotation - stars: solar-type -
starspots
Abstract:
By extending our previous study by Maehara et al. (2012,
Cat. J/other/Nat/485.478), we searched for superflares on G-type
dwarfs (solar-type stars) using Kepler data for a longer period
(500 days) than that (120 days) in our previous study. As a result, we
found 1547 superflares on 279 G-type dwarfs, which is much more than
the previous 365 superflares on 148 stars. Using these new data, we
studied the statistical properties of the occurrence rate of
superflares, and confirmed the previous results, i.e., the occurrence
rate (dN/dE) of superflares versus flare energy (E) shows a power-law
distribution with dN/dE∝E-α, where α∼2. It is
interesting that this distribution is roughly similar to that for
solar flares. In the case of the Sun-like stars (with surface
temperature 5600-6000K and slowly rotating with a period longer than
10 days), the occurrence rate of superflares with an energy of
1034-1035erg is once in 800-5000yr. We also studied long-term
(500 days) stellar brightness variation of these superflare stars and
found that in some G-type dwarfs the occurrence rate of superflares
was extremely high, ∼57 superflares in 500 days (i.e., once in
10 days). In the case of Sun-like stars, the most active stars show a
frequency of one superflare (with 1034erg) in 100 days. There is
evidence that these superflare stars have extremely large starspots
with a size about 10 times larger than that of the largest sunspot. We
argue that the physical origin of the extremely high occurrence rate
of superflares in these stars may be attributed to the existence of
extremely large starspots.
Description:
Kepler carries an optical telescope with a 95cm aperture and 105deg2
field-of-view (about 12° diameter), which is in Cygnus, Lyra, and
Draco. This spacecraft is designed to obtain high-precision and
long-period light curves of many stars. The typical precision is
0.1mmag for a star of 12mag and the number of observed stars is more
than 160000 (Koch et al. 2010ApJ...713L..79K 2010ApJ...713L..79K).
The data we used were taken during the period from 2009 May to 2010
September. We retrieved the data from the Multimission Archive at the
Space Telescope Science Institute and analyzed the long-cadence (the
time resolution is about 30 minutes) corrected flux of 9511, 75598,
82811, 82586, 89188, 86248, and 82052 stars in quarters 0, 1, 2, 3, 4,
5, and 6, respectively (all public light curves of G-type dwarfs
observed by Kepler). Since the aim of this study is to detect
superflares on G-type dwarfs, we selected G-type dwarfs in all of the
observed stars using the Kepler Input Catalog (Brown et al. 2011,
Cat. J/AJ/142/112). The condition is 5100K≤Teff<6000K and logg>4.0
and the number of selected stars is about 80000 in 160000.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 31 279 The 279 G-type dwarfs with superflares
(table added by CDS)
table7.dat 67 1547 Parameters of the observed flares
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
J/other/Nat/485.478 : Superflares on solar-type stars (Maehara+, 2012)
J/AJ/142/112 : KIC photometric calibration (Brown+, 2011)
J/AJ/141/50 : White-light flares on cool stars from Kepler (Walkowicz+, 2011)
http://archive.stsci.edu/kepler/data_release.html : Kepler DR archive
Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- KIC [2012690/12401269] Kepler identifier (Cat. V/133)
10- 13 I4 K Teff [5101/5999] Effective temperature
15- 17 F3.1 [cm/s2] log(g) [4/5] Log of the surface gravity
19- 21 F3.1 Rsun Rad [0.5/2] Stellar radius
23- 26 F4.1 mag Kpmag [10.6/16.4] Kepler band magnitude
28- 31 F4.1 d Prot [0.1/37]? Stellar rotational period (G1)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- KIC [2012690/12401269] Kepler identifier (Cat. V/133)
10- 13 I4 K Teff [5101/5999] Effective temperature
15- 17 F3.1 [cm/s2] log(g) [4/5] Log of the surface gravity
19- 21 F3.1 Rsun Rad [0.5/2] Stellar radius
23- 26 F4.1 mag Kpmag [10.6/16.4] Kepler band magnitude
28- 31 F4.1 d Prot [0.1/37]? Stellar rotational period (G1)
33- 38 F6.4 --- BVAmp [0.0003/0.21] Brightness variation amplitude (2)
40- 41 I2 --- Nf [1/57] Number of flares (3)
43- 50 F8.2 d Date Date of flare peak; BJD-2400000
52- 55 F4.1 --- FAmp [0.1/31] Flare amplitude (1)
57- 60 F4.2 d Dur [0.04/0.25] Duration (4)
62- 67 E6.2 10-7J E [1.2e+33/1.3e+36] Estimated bolometric flare
energy; in erg units
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Note (1): defined as ΔF/Fav = (F/Fav)-1, if Fav is the average flux.
Note (2): The amplitude of the brightness variaton corresponds to the
apparent fraction of the spot area to the disk area. It is defined
from the flux variations in the quarter ΔF(t)=F(t)-Fav (Fav
is the average flux) as: BVAmp=[max(ΔF)-min(ΔF)]/Fav,
after removing the 1% points with the largest |ΔF| values.
Note (3): Detected in whole observation period.
Note (4): Difference between flare-end-date and flare-start-date.
--------------------------------------------------------------------------------
Global Notes:
Note (G1): Estimated from brightness variation.
History:
From electronic version of the journal
References:
Notsu et al. Paper II. 2013ApJ...771..127N 2013ApJ...771..127N
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 18-Nov-2013