J/MNRAS/476/1224 Starspot variability as X-ray radiation proxy (Arkhypov+, 2018)
Starspot variability as an X-ray radiation proxy.
Arkhypov O.V., Khodachenko M.L., Lammer H., Gudel M., Luftinger T.,
Johnstone C.P.
<Mon. Not. R. Astron. Soc., 476, 1224-1233 (2018)>
=2018MNRAS.476.1224A 2018MNRAS.476.1224A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; X-ray sources ; Effective temperatures
Keywords: stars: activity - starspots - ultraviolet: stars - X-rays: stars
Abstract:
Stellar X-ray emission plays an important role in the study of
exoplanets as a proxy for stellar winds and as a basis for the
prediction of extreme ultraviolet (EUV) flux, unavailable for direct
measurements, which in their turn are important factors for the
mass-loss of planetary atmospheres. Unfortunately, the detection
thresholds limit the number of stars with the directly measured X-ray
fluxes. At the same time, the known connection between the sunspots
and X-ray sources allows using of the starspot variability as an
accessible proxy for the stellar X-ray emission. To realize this
approach, we analysed the light curves of 1729 main-sequence stars
with rotation periods 0.5<P<30d and effective temperatures
3236<Teff<7166K observed by the Kepler mission. It was found that the
squared amplitude of the first rotational harmonic of a stellar light
curve may be used as a kind of activity index. This averaged index
revealed practically the same relation with the Rossby number as that
in the case of the X-ray to bolometric luminosity ratio Rx. As a
result, the regressions for stellar X-ray luminosity Lx(P, Teff)
and its related EUV analogue LEUV were obtained for the
main-sequence stars. It was shown that these regressions allow
prediction of average (over the considered stars) values of log(Lx)
and log(LEUV) with typical errors of 0.26 and 0.22dex, respectively.
This, however, does not include the activity variations in particular
stars related to their individual magnetic activity cycles.
Description:
We use the empirical relation between Lx/L and A21 to predict the
stellar X-ray luminosity Lx(P,Teff) as a function of stellar rotation
period P and effective temperature Teff.
we outline our approach using an extended stellar sample and our
time-tested processing method (Arkhypov et. al. 2015A&A...576A..67A 2015A&A...576A..67A,
2015ApJ...807..109A 2015ApJ...807..109A, 2016ApJ...826...35A 2016ApJ...826...35A, 2018MNRAS.473L..84A 2018MNRAS.473L..84A).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 83 1729 The analysed stellar set, applied parameters,
and predictions
table3.dat 77 823 Parameters and predictions for stars in the
catalogue by Wright et al.
(2011ApJ...743...48W 2011ApJ...743...48W, Cat. J/ApJ/743/48)
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
J/ApJ/743/48 : Stars with rotation periods & X-ray luminosities (Wright+ 2011)
J/A+A/557/L10 : Rotation periods of 12000 Kepler stars (Nielsen+, 2013)
J/ApJS/211/24 : Rotation periods of Kepler MS stars (McQuillan+, 2014)
J/ApJS/229/30 : Q1-17 Kepler targets revised stellar properties (Mathur+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 I7 --- KIC KIC number
9- 12 I4 K Teff Stellar effective temperature from
Mathur et al. (2017ApJS..229...30M 2017ApJS..229...30M,
Cat. J/ApJS/229/30)
16- 21 F6.3 d P Rotation period (1)
23- 30 F8.5 [-] log() Our active index, averaged over a whole
light curve, A12
33- 42 F10.8 [-] e_log() Estimated error of log()
44- 51 F8.6 mag (B-V)o Colour index according to the transformation
Teff-->(B-V)o in equation (1)
54- 62 F9.6 d tauMLT Turnover time according to equation (4) in
Noyes et al. (1984ApJ...279..763N 1984ApJ...279..763N)
64- 72 F9.5 [-] log(Rx)reg Logarithm of the ratio of X-ray to bolometric
luminosities which are estimated from
equations (6)-(8) of the paper
75- 83 F9.6 [10-7W] log(Lx)reg Logarithm of the predicted X-ray luminosity
using equations (10)-(14) of the paper
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Note (1): Rotation period from McQuillan et al. (2014ApJS..211...24M 2014ApJS..211...24M,
Cat. J/ApJS/211/24) or Nielsen et al. (2013A&A...557L..10N 2013A&A...557L..10N,
Cat. J/A+A/557/L10) if absent in the first source.
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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- 9 F9.5 deg RAdeg ?=- Right ascension (J2000) for
epoch 2000.0 (1)
11- 19 F9.5 deg DEdeg ?=- Declination (J2000) for epoch 2000.0 (1)
21- 28 A8 --- Field Afiliation
31- 34 I4 K Teff Effective temperature (1)
37- 41 F5.2 d P Period (1)
43- 50 F8.5 d tauMLT Turnover time (2)
52- 59 F8.5 [-] log(Rx)reg Logarithm of the ratio of X-ray to bolometric
luminosities which are estimated from
equations (6)-(8) of the paper
62- 68 F7.4 [10-7W] log(Lx)reg Logarithm of the predicted X-ray luminosity
using equations (10)-(14) of the paper
71- 77 F7.4 [10-7W] log(Lx) Logarithm of the measured X-ray luminosity (1)
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Note (1): from Wright et al. (2011ApJ...743...48W 2011ApJ...743...48W, Cat. J/ApJ/743/48)
Note (2): Turnover time according to equation (4) in Noyes et al.
(1984ApJ...279..763N 1984ApJ...279..763N) and transform Tw-->(B-V)o (equation 26 in
Arkhypov et al., 2016ApJ...826...35A 2016ApJ...826...35A).
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 23-Apr-2021