J/A+A/639/A63 Active red giants asteroseismic & rotation param. (Gaulme+, 2020)
Active red giants: close binaries versus single rapid rotators.
Gaulme P., Jackiewicz J., Spada F., Chojnowski D., Mosser B., McKeever J.,
Hedlund A., Vrard M., Benbakoura M., Damiani C.
<Astron. Astrophys. 639, A63 (2020)>
=2020A&A...639A..63G 2020A&A...639A..63G (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, spectroscopic ; Stars, giant ; Asteroseismology ;
Stars, diameters ; Stars, masses ; Rotational velocities
Keywords: binaries: spectroscopic - stars: rotation - stars: oscillations -
techniques: radial velocities - techniques: photometric - starspots
Abstract:
Oscillating red-giant stars have provided a wealth of asteroseismic
information regarding their interiors and evolutionary states, and
access to their fundamental properties enable detailed studies of the
Milky Way. The objective of this work is to determine what fraction of
red-giant stars shows photometric rotational modulation, and
understand its origin. One of the underlying questions is the role of
close binarity in this population, standing upon the fact that red
giants in short-period binary systems (less than 150 days or so) have
been observed to display strong rotational modulation. We select a
sample of about 4500 relatively bright red giants observed by Kepler,
and show that about 370 of them (∼8%) display rotational modulation.
Almost all have oscillation amplitudes below the median of the sample,
while 30 of them are not oscillating at all. Of the 85 of these red
giants with rotational modulation chosen for follow-up radial-velocity
observation and analysis, 34 show clear evidence of spectroscopic
binarity. Surprisingly, 26 of the 30 non-oscillators are in this group
of binaries. To the contrary, about 85% of the active red giants with
detectable oscillations are not part of close binaries. With the help
of stellar masses and evolutionary states computed from the
oscillation properties, we shed light on the origin of their activity.
It appears that low-mass red-giant branch stars tend to be
magnetically inactive, while intermediate-mass ones tend to be highly
active. The opposite trends are true for helium-core burning (red
clump) stars, whereby the lower-mass clump stars are comparatively
more active and the higher-mass ones less so. In other words, we find
that low-mass red-giant branch stars gain angular momentum as they
evolve to clump stars, while higher-mass ones lose angular momentum.
The trend observed with low-mass stars leads to possible scenarios of
planet engulfment or other merging events during the shell-burning
phase. Regarding intermediate-mass stars, the rotation periods that we
measure are long with respect to theoretical expectations reported in
the literature, which reinforces the existence of an unidentified sink
of angular momentum after the main sequence. This article establishes
strong links between rotational modulation, tidal interactions,
(surface) magnetic fields, and oscillation suppression. There is a
wealth of physics to be studied in these targets not available in the
Sun.
Description:
To avoid as much as possible being influenced by observational biases,
a subsample of the RGs observed by the Kepler satellite during its
original four-year mission was carefully selected. This sample was
picked from the Berger et al. (2018, Cat. J/ApJ/866/99) stellar
classification of the Kepler field based on the Gaia DR2. From their
sample of RGs, we selected the targets whose light curves should not
be limited by the photon noise, meaning that the oscillations of a
regular RG should be detectable. This led us to consider the brightest
stars (mKep≤12.5mag) that were observed the longest (more than 3
years). We added a cut on radii, to make sure that the oscillation
range would fall between 15uHz and the sampling cut-off (Nyquist
frequency) at ∼283uHz. The final sample is composed of 4465 RG
stars.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablec1.dat 223 4574 Asteroseismic and rotational parameters
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
J/A+A/588/A87 : Seismic global parameters of 6111 KIC (Vrard+, 2016)
J/ApJ/866/99 : Revised radii of KIC stars + planets using Gaia DR2
(Berger+, 2018)
Byte-by-byte Description of file: tablec1.dat
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Bytes Format Units Label Explanations
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1- 9 I9 --- KIC KIC number
11- 27 A17 --- 2MASS 2MASS designation
29- 30 I2 h RAh Right Ascension (J2000)
31 A1 --- --- [:]
32- 33 I2 min RAm Right Ascension (J2000)
34 A1 --- --- [:]
35- 40 F6.3 s RAs Right Ascension (J2000)
42 A1 --- DE- Declination sign (J2000)
43- 44 I2 deg DEd Declination (J2000)
45 A1 --- --- [:]
46- 47 I2 arcmin DEm Declination (J2000)
48 A1 --- --- [:]
49- 53 F5.2 arcsec DEs Declination (J2000)
55- 59 F5.2 mag Kpmag Kepler magnitude
61- 64 I4 K Teff GAIA DR2 effective temperature
66- 68 I3 K e_Teff Error on Teff
70- 76 F7.2 uHz numax ?=-999 Oscillation frequency at maximum
amplitude
78- 84 F7.2 uHz e_numax ?=-999 Error on nu max
86- 92 F7.2 uHz Dnu ?=-999 Oscillation mean large frequency
separation
94-100 F7.2 uHz e_Dnu ?=-999 Error on Dnu
102-109 E8.3 uHz-1 Hmax ?=-999 Height of oscillation envelope
(in ppp2/muHz unit)
111-118 E8.3 uHz-1 e_Hmax ?=-999 Error on Hgauss
(in ppp2/muHz unit)
120-126 F7.2 Msun M* ?=-999 Asteroseismic mass
128-134 F7.2 Msun e_M* ?=-999 Error on M*
136-142 F7.2 Rsun R* ?=-999 Asteroseismic radius
144-150 F7.2 Rsun e_R* ?=-999 Error on R*
152-158 F7.2 [cm/s2] logg* ?=-999 Asteroseismic logg
160-166 F7.2 [cm/s2] e_logg* ?=-999 Error on logg*
168-174 F7.2 s DPi1 ?=-999 Period spacing of dipole mixed
modes
176-182 F7.2 --- visl1 ?=-999 Dipole (l=1) mode visibility
184-190 F7.2 % Sph ?=-999 Photometric index
192-198 F7.2 d Prot ?=-999 Rotation period
200-206 F7.2 km/s vsin90 ?=-999 Stellar equatorial rotation
velocity
208 I1 --- Nvisit Number of spectroscopic measurements
210-216 F7.2 km/s std(RV) ?=-999 Standard deviation of radial
velocities
218-219 I2 --- Flgact/osc ? Activity and oscillation flag (1)
221 I1 --- FlgVrard16 [0/1] Is 1 if the value of DPi1 comes from
Vrard et al., 2016, Cat. J/A+A/588/A87
223 I1 --- evolStatus ? Red giant evolutionary state (2)
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Note (1): Activity and oscillation flag as follows:
0 = no act. & osc.
1 = activity & no osc.
2 = clear activity & osc.
3 = possible act. & osc.
4 = binary signal in power spectrum of light curve
5 = no act. & no osc.
6 = classical pulsator
7 = heartbeat star
8 = double pulsator
14 = combination of 1 and 4
26 = combination of 2 and 6
54 = combination of 5 and 4
56 = combination of 5 and 6
60 = combination of 6 and 0
Note (2): Red giant evolutionary state as follows:
0 = unknown
1 = RGB
2 = RC
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Acknowledgements:
Patrick Gaulme, gaulme(at)mps.mpg.de
(End) Patricia Vannier [CDS] 04-Jun-2020