J/ApJ/916/66 K2 LCs analysis of Sun-like stars in the Pleiades (Brown+, 2021)
Brightness fluctuation spectra of Sun-like stars.
I. The mid-frequency continuum.
Brown T.M., Garcia R.A., Mathur S., Metcalfe T.S., Santos A.R.G.
<Astrophys. J., 916, 66 (2021)>
=2021ApJ...916...66B 2021ApJ...916...66B
ADC_Keywords: Clusters, open; Stars, masses; Effective temperatures;
Colors; Stars, G-type; Sun; Photometry, UBV; Infrared sources
Keywords: Stellar activity ; Stellar rotation ; Solar dynamo ;
Supergranulation
Abstract:
We analyze space-based time-series photometry of Sun-like stars,
mostly in the Pleiades, but also field stars and the Sun itself. We
focus on timescales between roughly 1hr and 1day. In the corresponding
frequency band these stars display brightness fluctuations with a
decreasing power-law continuous spectrum. K2 and Kepler observations
show that the rms flicker due to this mid-frequency continuum (MFC)
can reach almost 1%, approaching the modulation amplitude from active
regions. The MFC amplitude varies by a factor up to 40 among Pleiades
members with similar Teff, depending mainly on the stellar Rossby
number Ro. For Ro≤0.04, the mean amplitude is roughly constant at
about 0.4%; at larger Ro the amplitude decreases rapidly, shrinking by
about two orders of magnitude for Ro∼1. Among stars, the MFC amplitude
correlates poorly with that of modulation from rotating active
regions. Among field stars observed for 3yr by Kepler, the quarterly
average modulation amplitudes from active regions are much more time
variable than the quarterly MFC amplitudes. We argue that the process
causing the MFC is largely magnetic in nature and that its power-law
spectrum comes from magnetic processes distinct from the star's global
dynamo, with shorter timescales. By analogy with solar phenomena, we
hypothesize that the MFC arises from a (sometimes energetic) variant
of the solar magnetic network, perhaps combined with rotation-related
changes in the morphology of supergranules.
Description:
NASA's K2 mission targeted M45 (the Pleiades open cluster) during K2
Campaign 4, running from 2015 February 7 to April 23.
We selected 101 stars to be analyzed from the list of 759 Pleiades
stars with reliable rotation periods from Rebull+ (2016, J/AJ/152/113).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 103 113 Star sample physical and fitted parameters
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See also:
IV/34 : K2 Ecliptic Plane Input Catalog (EPIC) (Huber+, 2017)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
III/284 : APOGEE-2 data from DR16 (Johnsson+, 2020)
J/ApJS/224/2 : K2 EPIC stellar properties for 138600 targets (Huber+, 2016)
J/MNRAS/408/475 : HATNet Pleiades Rotation Period Catalogue (Hartman+, 2010)
J/ApJ/743/48 : Stars with rot. periods & X-ray luminosities (Wright+, 2011)
J/A+A/572/A34 : Pulsating solar-like stars in Kepler (Garcia+, 2014)
J/ApJS/211/24 : Rotation periods of Kepler MS stars (McQuillan+, 2014)
J/MNRAS/456/2260 : K2 Variability Catalogue II (Armstrong+, 2016)
J/ApJS/224/2 : K2 EPIC stellar properties for 138600 targets (Huber+, 2016)
J/AJ/152/113 : Pleiades members with K2 LCs. I. Periods (Rebull+, 2016)
J/AJ/152/114 : Pleiades members with K2 light curves. II. (Rebull+, 2016)
J/AJ/152/115 : Pleiades members with K2 LCs. III. (Stauffer+, 2016)
J/ApJ/835/172 : Kepler asteros. LEGACY sample. I. Oscillations (Lund+, 2017)
J/ApJ/835/173 : Kepler asteroseismic LEGACY sample. II. (Silva Aguirre+, 2017)
J/AJ/155/23 : Low-mass fast rotators in solar neighborhood (Saylor+, 2018)
J/ApJS/237/17 : Temporal frequency shifts in 87 Kepler stars (Santos+, 2018)
J/ApJS/243/28 : M-type star activities from LAMOST & Kepler (Lu+, 2019)
J/ApJS/244/21 : Surface rot. & activity of Kepler stars. I. (Santos+, 2019)
J/ApJS/247/28 : K2 star param. from Gaia & LAMOST (Hardegree-Ullman+, 2020)
J/ApJS/251/23 : K2 GAP DR2: campaigns 4, 6 & 7 (Zinn+, 2020)
J/A+A/635/A43 : Stellar rot. periods from K2 Campaigns 0-18 (Reinhold+, 2020)
http://doi.org/10.17909/T9N889 : K2 Campaign 4 LCs on MAST.
http://webda.physics.muni.cz/navigation.html : WEBDA database
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name Star name
15- 19 I5 --- Hz [25/10853]? Hertzsprung Catalog number (1)
21- 29 F9.5 deg RAdeg ?=0 Right Ascension (J2000)
31- 38 F8.5 deg DEdeg ?=0 Declination (J2000)
40- 44 F5.2 mag Vmag [-1/17] Apparent Johnson V band magnitude
from Rebull+ (2016, J/AJ/152/113)
46- 49 F4.2 mag (V-K) [0.99/5.11] The (V-K) color index
from Rebull+ (2016, J/AJ/152/113)
51- 54 F4.2 Msun Mass [0.26/1.63] Stellar mass
56- 59 I4 K Teff [3578/6711] Effective temperature from
APOGEE (2)
61- 64 F4.2 [cm/s2] logg [3.1/5.02] log surface gravity from APOGEE (2)
66- 70 F5.2 d Prot [0.23/42] Rotational period
from Rebull+ (2016, J/AJ/152/113)
72- 76 F5.3 --- Ro [0.005/2.15] Rossby number (Ro=Prot/τc;
with τc, the turnover time for the
stellar convection zone. See Section 4)
78- 79 A2 --- Bin Binarity flag (3)
81- 84 A4 --- Mem Pleiades membership class (4)
86- 87 A2 --- Cdnc Observing cadence (5)
89- 92 F4.2 [ppm] logsigH [1.82/4.65] log total harmonic RMS
94- 97 F4.2 [ppm] logsigC [1.19/3.86] log continuum RMS
99-103 F5.3 --- alpha1 [0.49/5.57] MFC power law index
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Note (1): From WEBDA (Paunzen 2008CoSka..38..435P 2008CoSka..38..435P -- where the numbering
is based on Hertzsprung 1947AnLei..19A...1H 1947AnLei..19A...1H).
Note (2): Three of our selected stars did not have APOGEE data; for those we
used parameter values from the MAST EPIC catalog
(Huber+ 2016, J/ApJS/224/2). See Section 3.1.
Note (3): Binarity flag as follows:
s = single (80 occurrences);
pb = possible binary (8 occurrences);
b = probable binary (25 occurrences).
Note (4): Membership class (from Rebull+ 2016, J/AJ/152/113 ; see Section 3.1)
as follows:
best = very likely member (69 occurrences);
ok = likely member (8 occurrences);
nm = not member (36 occurrences).
Note (5): Observing cadence as follows:
LC = long cadence {~=}30min;
SC = short cadence {~=}1min.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 29-Dec-2022