J/A+A/645/A42 Flares in 5 open clusters (Ilin+, 2021)
Flares in open clusters with K2.
II. Pleiades, Hyades, Praesepe, Ruprecht 147, and M67.
Ilin E., Schmidt S.J., Poppenhager K., Davenport J.R.A., Kristiansen M.H.,
Omohundro M.
<Astron. Astrophys. 645, A42 (2021)>
=2021A&A...645A..42I 2021A&A...645A..42I (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Stars, dwarfs ; Stars, variable ;
Photometry, photographic ; Effective temperatures
Keywords: stars: activity - stars: flare - stars: low-mas - stars: rotation -
methods: data analysis
Abstract:
Magnetic fields are a key component in the main sequence evolution of
low mass stars. Flares, energetic eruptions on the surfaces of stars,
are an unmistakable manifestation of magnetically driven emission. The
occurrence rates and energy distributions of flares trace stellar
characteristics such as mass and age. But before flares can be used to
constrain stellar properties, the flaring-age-mass relation requires
proper calibration. This work sets out to quantify flaring activity of
independently age-dated main sequence stars for a broad range of
spectral types using optical light curves obtained by the Kepler
satellite. Drawing from the complete K2 archive, we searched 3435 80
day long light curves of 2111 open cluster members for flares using
the open-source software packages K2SC to remove instrumental and
astrophysical variability from K2 light curves, and AltaiPony to
search and characterize the flare candidates. We confirmed a total of
3844 flares on high probability open cluster members with ages from
zero age main sequence (Pleiades) to 3.6Gyr (M67). We extended the
mass range probed in the first study of this series to span from
Sun-like stars to mid-M dwarfs. We added the Hyades (690Myr) to the
sample as a comparison cluster to Praesepe (750Myr), the 2.6Gyr old
Ruprecht 147, and several hundred light curves from the late K2
Campaigns in the remaining clusters. We found that the flare energy
distribution was similar in the entire parameter space, following a
power law relation with an exponent between 1.84 and 2.39. We
confirmed that flaring rates declined with age, and declined faster
for higher mass stars. Our results are in good agreement with most
previous statistical flare studies. We found evidence that a rapid
decline in flaring activity occurred in M1-M2 dwarfs around
Hyades/Praesepe age, when these stars spun down to rotation periods of
about 10 d, while higher mass stars had already transitioned to lower
flaring rates, and lower mass stars still resided in the saturated
activity regime. We conclude that some discrepancies between our
results and flare studies that used rotation periods for their age
estimates could be explained by sample selection bias toward more
active stars, but others may hint at limitations of using rotation as
an age indicator without additional constraints from stellar activity.
Description:
K2 30 minute cadence light curves were searched for flares using the
open source software AltaiPony.
stars.dat gives the relevant properties for all stars, flares.dat
contains the full list of flares with their respective equivalent
durations, amplitudes and times (Table 2 in the paper). ffds.dat
contains the results from the power law fits to flare frequency
distributions in individual cluster and effective temperature bins
(Table 3 in the paper).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
stars.dat 95 2111 Stellar parameters
flares.dat 176 3844 Stellar flares law fit parameters (table 2)
ffds.dat 211 22 Flare frequency distributions and power law fit
parameters (table 3)
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See also:
J/A+A/622/A133 : M45, M44 and M67 flare stars (Ilin+, 2019)
Byte-by-byte Description of file: stars.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 I9 --- ID EPIC ID
11- 12 I2 --- Campaign K2 observing campaign
14- 22 F9.5 deg RAdeg Right Ascension (J2000)
24- 32 F9.5 deg DEdeg Declination (J2000)
34- 37 F4.2 --- Pmemb [0.8/1.0] Mean membership probability (1)
39- 42 I4 K Teff [2780/5997] Stellar effective temperature
44- 46 I3 K e_Teff Uncertainty on effective temperature
48- 51 F4.2 Rsun R [0.13/1.15] stellar radius
53- 56 F4.2 Rsun e_R Uncertainty on stellar radius
58- 65 E8.3 10-7W Lbol Projected stellar bolometric luminosity
67- 74 E8.3 10-7W e_Lbol Uncertainty on projected stellar bolometric
luminosity
77- 84 E8.3 10-7W LKepler Projected stellar luminosity in the Kepler band
88- 95 E8.3 10-7W e_LKepler Uncertainty on projected stellar luminosity in
the Kepler band
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Note (1): See Table A1 and Figure A1 in the Appendix of the paper for membership
catalogs used to select high probability members in each open cluster.
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Byte-by-byte Description of file: flares.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 I9 --- ID EPIC ID
11- 12 I2 --- Campaign K2 observing campaign
14- 19 I6 --- cstart Flare start cadence number
21- 26 I6 --- cstop Flare end cadence number
28- 43 F16.11 d tstart Flare start time,
Barycentric Kepler Julian Date
45- 60 F16.11 d tstop Flare stop time,
Barycentric Kepler Julian Date
62- 69 F8.2 s ED [1.82/82185] Measured equivalent duration
71- 76 F6.2 s e_ED Uncertainty on ED
78- 83 F6.4 --- Ampl-rec [0.0003/9.6748] Measured relative flare
amplitude
87-112 A26 --- Note Note saturation of the detector
114-117 I4 --- dtp Number of accepted data points in light curve
119-128 E10.3 10-7W LKepler Stellar luminosity in the Kepler band
130-139 E10.3 10-7W e_LKepler Uncertainty on Lum_Kepler
140-143 I4 K Teff-med [2780/5996] Effective temperature
145-147 I3 K e_Teff-med Uncertainty on Teff-med
149-157 E9.3 10-7W Lbol Stellar bolometric luminosity
159-167 E9.3 10-7W e_Lbol Uncertainty on bolometric luminosity
169-176 A8 --- Cluster Open cluster name
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Byte-by-byte Description of file: ffds.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 K Teffmin [2500/5000] Minimum effective temperature
in bin
6- 9 I4 K Teffmax [3000/6000] Maximum effective temperature
in bin
11- 18 A8 --- Cluster Open cluster name
20- 23 F4.2 --- alpha [1.84/2.31] FFD power law index in
ED space (1)
25- 28 F4.2 --- E_alpha Upper uncertainty on alpha (1)
30- 33 F4.2 --- e_alpha Lower uncertainty on alpha (1)
35- 41 F7.2 1/s beta [0.85/4707.79] FFD intercept in ED space (1)
43- 50 F8.2 1/s E_beta Upper uncertainty on beta (1)
52- 58 F7.2 1/s e_beta Lower uncertainty on beta (1)
60- 62 I3 --- Nflares [1/970] Number of flares in bin
64- 66 I3 --- Nfit [1/612] Number of flares used in FFD fit
68- 71 I4 Myr Age [135/3639] Open cluster age (2)
73- 75 I3 Myr E_Age Upper uncertainty on open cluster age
77- 79 I3 Myr e_Age Upper uncertainty on open cluster age
81- 87 F7.2 s EDmin [9.9/1236] Minimum equivalent duration
used in fit
89- 96 F8.2 s EDmax [59/82185] Maximum equivalent duration
used in fit
98-101 F4.2 --- alpha-en [1.86/2.39] FFD power law index in
energy space (1)
103-106 F4.2 --- E_alpha-en Upper uncertainty on alpha-en (1)
108-111 F4.2 --- e_alpha-en Lower uncertainty on alpha-en (1)
113-131 E19.14 1/s beta-en [1.28E+28/4.44E+45] FFD intercept in
energy space (1)
133-151 E19.14 1/s E_beta-en Upper uncertainty on beta_en (1)
153-171 E19.14 1/s e_beta-en Lower uncertainty on beta_en (1)
173-175 I3 --- Nflares-en [1/970] Number of flares in bin
(energy space)
177-179 I3 --- Nfit-en [1/663] Number of flares used in FFD fit
(energy space)
181-184 F4.2 --- alphaD [1.47/2.18] FFD power law index from
Davenport et al., 2019ApJ...871..241D 2019ApJ...871..241D
186-193 E8.3 1/s betaD [7.29E+16/9.24E+39] FFD intercept from
Davenport et al., 2019ApJ...871..241D 2019ApJ...871..241D
195-202 E8.3 10-7J EKpmin [9.01E+31/6.25E+33] Minimum energy used
in fit
204-211 E8.3 10-7J EKpmax [3.80E+32/3.01E+35] Maximum energy used
in fit
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Note (1): For M67, we used the prior values for alpha and alpha-en to determine
beta and beta-en directly from Eq. 3 in the paper.
Note (2): See Table B1 in Appendix of the paper for a literature overview over
open cluster ages, metallicities, and distances.
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Acknowledgements:
Ekaterina Ilin, eilin(at)aip.de
History:
Ilin et al., Paper I 2019A&A...622A.133I 2019A&A...622A.133I, Cat. J/A+A/622/A133
(End) Ekaterina Ilin [AIP, Germany], Patricia Vannier [CDS] 16-Oct-2020