J/A+A/642/A225 Faculae-Spot dominance & rotation periods (Amazo-Gomez+, 2020)
Inflection point in the power spectrum of stellar brightness variations.
III. Faculae versus spot dominance on stars with known rotation periods.
Amazo-Gomez E.M., Shapiro A.I., Solanki S.K., Kopp G., Oshagh M.,
Reinhold T., Reiners A.
<Astron. Astrophys. 642, A225 (2020)>
=2020A&A...642A.225A 2020A&A...642A.225A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Photometry
Keywords: stars: rotation - stars: solar-type - methods: observational -
techniques: photometric
Abstract:
Stellar rotation periods can be determined by observing brightness
variations caused by active magnetic regions transiting visible
stellar disk as the star rotates. The successful stellar photometric
surveys stemming from the Kepler and TESS observations led to the
determination of rotation periods in tens of thousands of young and
active stars. However, there is still a lack of information about
rotation periods of older and less active stars, like the Sun. The
irregular temporal profiles of light curves caused by the decay times
of active regions, which are comparable to or even shorter than
stellar rotation periods, combine with the random emergence of active
regions to make period determination for such stars very difficult.
We tested the performance of the new method for the determination of
stellar rotation periods against stars with previously determined
rotation periods. The method is based on calculating the gradient of
the power spectrum (GPS) and identifying the position of the
inflection point (i.e. point with the highest gradient). The GPS
method is specifically aimed at determining rotation periods of
low-activity stars like the Sun.
We applied the GPS method to Sun-like stars observed by the Kepler
telescope. We separately considered two stellar samples: one with
near-solar rotation periods (24-27.4d) and broad range of effective
temperatures (5000-6000K), another with near-solar effective
temperatures (5700-5900K) and broad range of rotation periods
(15-40d).
We show that the GPS method returns precise values of stellar rotation
periods. Furthermore, it allows us to constrain the ratio between
facular and spot areas of active regions at the moment of their
emergence. We show that relative facular area decreases with stellar
rotation rate.
Our results suggest that the GPS method can be successfully applied to
retrieve periods of stars with both regular and non-regular light
curves.
Description:
This table contains an example of the GPS outputs, the compared
rotation period values from GLS and ACF, and stellar parameters for
Kepler stars.
In column 4 and 5 values of alpha-factor and its 2-sigma uncertainty
are reported respectively. Prot GPS values in column 6, as result of
applying Eq. 1 using the factor alpha=0.19. 2) Column 7 shows the Prot
reported by Reinhold & Gizon (2015, Cat. J/A+A/583/A65). 3) Prot and
variability values reported by McQuillan et al. (2014, Cat.
J/ApJS/211/24) in column 8. 4) Columns 10, 11 and 12 show the logg,
[Fe/H], and Teff respectively, taken from Huber et al. (2014, Cat
J/ApJS/211/2).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 97 1047 Faculae-Spot dominance & rotation periods
(GPS outcome values)
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
J/ApJS/211/2 : Q1-16 Kepler targets revised stellar properties (Huber+, 2014)
J/ApJS/211/24 : Rotation periods of Kepler MS stars (McQuillan+, 2014)
J/A+A/583/A65 : Active Kepler stars differential rotation (Reinhold+, 2015)
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 ID star Designation
10- 16 F7.5 d PHFIP High Frequency Inflection Point period (1) (2)
18- 25 F8.6 d e_PHFIP High Frequency Inflection Point period
2-sigma uncertainty
27- 34 F8.6 --- alpha alpha factor (1)
36- 44 F9.7 --- e_alpha alpha factor 2-sigma uncertainty
46- 52 F7.4 d ProtGPS Rotation period by GPS (3)
54- 60 F7.4 d ProtGLS ? Rotation period by GLS (4)
62- 68 F7.4 d ProtACF Rotation period by ACF (5)
70- 77 F8.2 ppm Var Variability amplitude within 1 period (5)
79- 85 F7.5 [cm/s2] logg Surface gravity (6)
87- 92 F6.3 [-] [Fe/H] Metallicity (6)
94- 97 I4 K Teff Effective temperature (6)
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Note (1): we suggested that the period PHFIP, corresponding to the maximum of
the gradient of the power spectrum (GPS) (i.e. to the inflection point) in the
high-frequency tail could be used to identify the stellar rotation period,
Prot, via the simple scaling relation: Prot=PHFIP/alpha.
Note (2): High Frequency Inflection Point period defined from individual
inflection points for each Kepler observing quarter.
Note (3): Rotation period by GPS, s result of applying Eq. 1 using the
factor alpha=0.19.
Note (4): Rotation period reported by Reinhold & Gizon
(2015, Cat. J/A+A/583/A65).
Note (5): Prot and variability values reported by McQuillan et al.
(2014, Cat. J/ApJS/211/24).
Note (6): taken from Huber et al. (2014, Cat J/ApJS/211/2).
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Acknowledgements:
Eliana Amazo-Gomez, amazo(at)mps.mpg.de
References:
Shapiro et al., Paper I 2020A&A...633A..32S 2020A&A...633A..32S
Amazo-Gomez et al., Paper II 2020A&A...636A..69A 2020A&A...636A..69A
(End) Eliana Amazo-Gomez [MPS], Patricia Vannier [CDS] 13-Oct-2020