J/MNRAS/447/2714 Flare stars across the H-R diagram (Balona+, 2015)
Flare stars across the H-R diagram.
Balona L.A.
<Mon. Not. R. Astron. Soc., 447, 2714-2725 (2015)>
=2015MNRAS.447.2714B 2015MNRAS.447.2714B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, flare ; Stars, variable
Keywords: stars: activity - stars: flare - stars: magnetic field - starspots
Abstract:
From Kepler data, we show that the incidence of flares on stars drops
by only a factor of 4 from K-M dwarfs to A-F stars. Allowing for
visibility effects, this implies that the true relative number of
flare stars does not change very much from cool dwarfs to hot A stars.
The idea that flares on A stars can be attributed to a cool companion
has to be rejected because it leads to flare amplitudes two orders of
magnitude smaller than actually observed. We confirm that spots on
flare stars are generally larger than those on non-flare stars and
that flare stars rotate significantly faster than non-flare stars.
Analysis of 209 flare stars observed in Kepler short-cadence mode
allows accurate measurements of flare shapes and duration. We find
that about one-third of the flares have a bump or slope discontinuity
on the decaying branch and that flares of long duration are to be
found in stars with low surface gravities. Flare energies are strongly
correlated with stellar luminosity and radius. The correlation with
radius leads to a rough estimate of several tens of gauss for the
typical magnetic field associated with a flare. The correlation with
stellar luminosity can be understood if the typical flare loop
length-scales approximately as the stellar radius. We examined the
flare frequency as a function of orbital phase in three eclipsing
binaries in which a large number of flares are visible. There appears
to be no correlation of flaring with orbital phase, which weakens the
hypothesis that flares in close binaries could be a result of
reconnection of field lines connecting the two stars.
Description:
Parameters of 3140 flares in 209 stars observed by Kepler in
short-cadence mode. This analysis made use of the public releases of
quarter 0-17 short-cadence light curves, which were downloaded from
the Kepler mission archive.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 63 209 Flare stars observed in SC mode,
stellar parameters
table3.dat 44 209 Flare stars observed in SC mode, parameters
of the strongest flare in each star
table1.dat 45 3140 Parameters of flares measured in short-cadence
Kepler observations for 209 stars
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 8 I8 --- KIC KIC number
10- 14 F5.2 mag kepmag Kepler magnitude
16- 19 I4 K Teff Effective temperature
21- 25 F5.3 [cm/s2] logg Surface gravity
27- 33 A7 --- Type Variable type (1)
35- 40 F6.3 d Prot ?=- Rotation period
41 A1 --- u_Prot Uncertainty flag on Prot
43- 50 F8.4 d Porb ?=- Orbital period
52- 63 A12 --- Notes Notes
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Note (1): The variability classification is as follows:
ROT = rotational variable
DSCT = Scuti star
E = eclipsing star
EA = detached eclipsing binary
EB = semi-detached eclipsing binary
SOL = solar-like oscillations
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 8 I8 --- KIC Kepler Input Catalog identifier
10- 15 F6.3 [h] log(EW) Total integrated flux of the flare (G1)
17- 22 F6.3 --- log(DF/F) Relative flare intensity
24- 28 F5.2 [h] Dt Total flare duration
30- 34 F5.2 [10-7W] log(E) Flare energy
36- 40 F5.3 d-1 f Flare frequency (in flare/d)
42- 44 I3 --- NFlare Number of flares
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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- 8 I8 --- KIC Kepler Input Catalog identifier
10- 17 F8.3 d tmax Time of flare maximum (BJD-2450000)
19- 24 F6.3 [h] log(EW) Total integrated flux of the flare (G1)
26- 31 F6.3 --- log(DF/F) Relative flare intensity
33- 38 F6.3 [h] Dt Total flare duration
40- 45 F6.3 [10-7W] log(E) Flare energy
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Global notes:
Note (G1): The integrated flux was measured by summing the flare intensity
relative to the background over the duration of the flare.
EW=Sumtime{F-FB)/F}.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 09-Sep-2015