J/ApJ/883/88 Short-duration stellar flares from GALEX & Kepler (Brasseur+, 2019)
Short-duration stellar flares in GALEX data.
Brasseur C.E., Osten R.A., Fleming S.W.
<Astrophys. J., 883, 88 (2019)>
=2019ApJ...883...88B 2019ApJ...883...88B
ADC_Keywords: Stars, flare; Stars, distances; Stars, diameters; Ultraviolet;
Optical; Stars, G-type
Keywords: stars: activity ; stars: chromospheres ; stars: flare ;
stars: magnetic field ; stars: solar-type ; ultraviolet: stars
Abstract:
We report on a population of short-duration near-ultraviolet (NUV)
flares in stars observed by the Kepler and Galaxy Evolution Explorer
(GALEX) missions. We analyzed the NUV light curves of 34276 stars
observed from 2009 to 2013 by both the GALEX (NUV) and Kepler
(optical) space missions with the eventual goal of investigating
multiwavelength flares. From the GALEX data, we constructed light
curves with a 10s cadence, and we ultimately detected 1904
short-duration flares on 1021 stars. The vast majority (94.5%) of
these flares have durations less than 5 minutes, with flare flux
enhancements above the quiescent flux level ranging from 1.5 to 1700.
The flaring stars are primarily solar-like, with Teff ranging from
3000 to 11000K and radii between 0.5 and 15R☉. This set of
flaring stars is almost entirely distinct from that of previous flare
surveys of Kepler data and indicates a previously undetected
collection of small flares contained within the Kepler sample. The
range in flare energies spans 1.8x1032-8.9x1037erg, with
associated relative errors spanning 2%-87%. The flare frequency
distribution by energy follows a power law with index
α=1.72±0.05, consistent with results of other solar and
stellar flare studies at a range of wavelengths. This supports the
idea that the NUV flares we observed are governed by the same physical
processes present in solar and optical flares. The relationship
between flare duration and associated flare energy extends results
found for solar and stellar white-light flares, and suggests that
these flares originate in regions with magnetic field strengths of
several hundred Gauss, and length scales of the order of 1010cm.
Description:
The GALEX was an orbiting space telescope active between 2003 April
and 2013 June.
The main Kepler mission ran from 2009 to 2013.
Due to the failure of GALEX's FUV camera in 2009 May, all GALEX data
simultaneous with Kepler observations are NUV only, spanning the range
1771-2831Å.
We compiled a list of 59366 objects observed by both GALEX and Kepler
from the Consolidated Input Values table in Huber+ (2014, J/ApJS/211/2),
cross-matched against the MAST KGMatch table
(http://archive.stsci.edu/pub/kepler/catalogs/README_KGMATCH).
We selected a final list of 34276 targets simultaneously observed by
Kepler and GALEX and extract light curves for each of those targets
(see Section 2).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 138 1705 All detected and vetted flares with
calculated energies for 942 KIC stars
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
II/335 : Revised catalog of GALEX UV sources (GUVcat_AIS GR6+7) (Bianchi+ 2017)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer- Jones+, 2018)
J/ApJ/448/683 : Hyades RASS observations (Stern+ 1995)
J/AJ/142/112 : KIC photometric calibration (Brown+, 2011)
J/other/Nat/485.478 : Superflares on solar-type stars (Maehara+, 2012)
J/ApJ/754/4 : HST monitoring of flaring stars in the bulge (Osten+, 2012)
J/ApJS/207/15 : M dwarf flare spectra (Kowalski+, 2013)
J/ApJS/209/5 : Superflares of Kepler stars. I. (Shibayama+, 2013)
J/ApJS/211/2 : Stellar properties of Q1-16 Kepler targets (Huber+, 2014)
J/ApJS/211/24 : Rotation periods of Kepler MS stars (McQuillan+, 2014)
J/MNRAS/447/2714 : Flare stars across the H-R diagram (Balona+, 2015)
J/ApJ/813/100 : Deep GALEX NUV survey of Kepler field. I. (Olmedo+, 2015)
J/ApJ/829/23 : Stellar flares from Q0-Q17 Kepler LCs (Davenport, 2016)
J/ApJ/851/91 : Studies of solar white-light flares (Namekata+, 2017)
J/ApJ/866/99 : Radii of KIC stars & planets using Gaia DR2 (Berger+, 2018)
J/A+A/620/A55 : Magnetic flaring from PMS stars spectra (Flaccomio+, 2018)
J/ApJ/858/55 : K2 ultracool dwarfs survey. III. Flares (Paudel+, 2018)
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 Input Catalog ID number of star
10- 28 I19 --- GID GALEX Catalog ID number of star
30- 38 I9 --- Start [926132291/999944565] Start time of flare (1)
40- 48 I9 --- End [926132401/999944606] End time of flare (1)
50- 56 E7.1 pc Dist [58/11000] Estimated distance (2)
58- 64 E7.1 pc e_Dist [57/9100] Lower bound of Dist (2)
66- 72 E7.1 pc E_Dist [58/14000] Upper bound of Dist (2)
74- 78 F5.2 Rsun Rad [0.47/15]? Stellar radius (3)
80- 84 I5 K Teff [3519/11928]? Effective temperature (4)
86- 93 E8.2 cW/m2/nm QFlux [1e-17/2.4e-14] Quiescent flux;
in erg/s/cm2/Å units (5)
95- 99 E5.0 cW/m2/nm e_QFlux [3e-18/5e-16] Standard error of the mean
in QFlux
101-108 E8.2 10-7W Lum [2e+28/9.5e+33] NUV stellar luminosity; erg/s
110-114 E5.0 10-7W e_Lum [3e+27/2e+33] Uncertainty in Lum
116-122 E7.1 10-7J Ebol [1.8e+32/9e+37] Estimated bolometric energy;
in erg units
124-130 E7.1 10-7J e_Ebol [1.6e+32/5.6e+37] Lower bound of Ebol (6)
132-138 E7.1 10-7J E_Ebol [2e+32/1.4e+38] Upper bound of Ebol (7)
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Note (1): In GALEX time (GALEX time = UNIX time - 315964800).
Note (2): From Magan Bedall's Kepler/GAIA crossmatch: http://gaia-kepler.fun/
Distances from Bailer-Jones+ (2018AJ....156...58B 2018AJ....156...58B ; Cat. I/347).
Note (3): Radii from Berger, Gaidos & van Saders 2018, J/ApJ/866/99
Note (4): From the Kepler Input Catalog (see V/133)
http://archive.stsci.edu/kepler/kic.html
Note (5): The mean flux after all flares are removed from the light curve.
Note (6): Based on Gaia DR2 (I/345) lower bound distance.
Note (7): Based on Gaia DR2 (I/345) upper bound distance.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 04-Mar-2021