J/A+A/668/A167 Superflares on solar-like stars (Vasilyev+, 2022)
Superflares on solar-like stars:
A new method for identifying the true flare sources in photometric surveys.
Vasilyev V., Reinhold T., Shapiro A.I., Krivova N.A., Usoskin I.,
Montet B.T., Solanki S.K., Gizon L.
<Astron. Astrophys. 668, A167 (2022)>
=2022A&A...668A.167V 2022A&A...668A.167V (SIMBAD/NED BibCode)
ADC_Keywords: Stars, flare ; Stars, G-type
Keywords: methods: data analysis - stars: solar-type - stars: flare -
stars: activity
Abstract:
Over the past years, thousands of stellar flares have been detected by
harvesting data from large photometric surveys. These detections,
however, do not account for potential sources of contamination such as
background stars appearing in the same aperture as the primary target.
We present a new method for identifying the true flare sources in
large photometric surveys using data from the Kepler mission.
Potential flares are identified in two steps: first, we search the
light curves for at least two subsequent data points exceeding a
5σ threshold above the running mean. For these two cadences, we
subtract the "quiet" stellar flux from the Kepler pixel data to obtain
new images where the potential flare is the main light source. In the
second step, we use a Bayesian approach to fit the point spread
function of the instrument to determine the most likely location of
the flux excess on the detector. We applied our method to 5862
main-sequence stars with near-solar effective temperatures. We found
2274 events exceeding the 5-sigma in at least two consecutive points
in the light curves. Applying the second step reduced this number to
342 superflares. Of these, 283 flares happened on 178 target stars, 47
events are associated with fainter background stars, and in 10 cases,
the flare location cannot be distinguished between the target and a
background star. We also present cases where flares have been reported
previously but our technique could not attribute them to the target
star. We conclude that 1) identifying outliers in the light curves
alone is insufficient to attribute them to stellar flares and 2)
flares can only be uniquely attributed to a certain star when the
instrument pixel-level data together with the point spread function
are taken into account. As a consequence, previous flare statistics
are likely contaminated by instrumental effects and unresolved
astrophysical sources.
Description:
We presented a new method to identify the flare location in the target
pixel files using the PSF-fitting procedure. Previous flare detection
methods were mostly based on the analysis of the light curves only.
Our light curve analysis detected 2274 cases that could potentially be
interpreted as a flare on the target star. However, the PSF-fitting of
the pixel data revealed that for more than 1900 of these cases the
target star was not enclosed in the ellipses for both cadences tflare
and tflare+Δt. Thus, the flux excess detected in the light
curve might arise from some other source of contamination, and cannot
be uniquely attributed to the target star. Even after the PSF-fitting
of the pixel data, not all detected flares can be associated with the
target star. Of the 342 detected flares, only 283 actually happened on
the 178 target stars, while the remaining cases either happened on a
fainter background star or cannot be uniquely attributed. Out of these
283 events, 45 flares happened on 22 stars for which rotational
periods have been measured by McQuillan et al. (2014ApJS..211...24M 2014ApJS..211...24M,
Cat. J/ApJS/211/24), and 238 flares occurred on 156 solar-like stars
with unknown rotation periods.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 84 340 The catalog of detected flares for 210 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 Kepler KIC number of the target star
10- 28 I19 --- GaiaDR2 Gaia DR2 ID of the target star
30- 37 F8.3 d Time Time when the flare starts
39- 44 F6.2 min dt Duration of the flare
46- 54 E9.2 10-7J Energy ?=-9.99E+02 Flare energy
56- 62 F7.2 d Prot ?=-999 Rotation period of the target star
measured by McQuillan et al.
(2014ApJS..211...24M 2014ApJS..211...24M, Cat. J/ApJS/211/24)
64 I1 --- Type [1/3] Classification flag for flare (1)
66- 84 I19 --- GaiaDR2Bckg ?=-999 GAIA DR2 ID of background stars for
types 2 and 3
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Note (1): Classification flag for flare as follows:
1 = flare associated to the target star
2 = flare associated to a background star
3 = flare that location cannot be distinguished between the target
and a background star
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Acknowledgements:
Valeriy Vasilyev, vasilyev(at)mps.mpg.de
(End) Patricia Vannier [CDS] 25-Oct-2022