J/A+A/668/A116 S-index for 3130 red giant stars (Gehan+, 2022)
Surface magnetism of rapidly rotating red giants:
Single versus close binary stars.
Gehan C., Gaulme P., Yu J.
<Astron. Astrophys. 668, A116 (2022)>
=2022A&A...668A.116G 2022A&A...668A.116G (SIMBAD/NED BibCode)
ADC_Keywords: Asteroseismology ; Stars, giant ; Optical
Keywords: asteroseismology - methods: data analysis - techniques: spectroscopy -
stars: activity - stars: chromospheres - binaries: general
Abstract:
According to dynamo theory, stars with convective envelopes
efficiently generate surface magnetic fields, which manifest as
magnetic activity in the form of starspots, faculae, flares, when
their rotation period is shorter than their convective turnover time.
Most red giants, having undergone significant spin down while
expanding, have slow rotation and no spots. However, based on a sample
of about 4500 red giants observed by the NASA Kepler mission, a
previous study showed that about 8% display spots, including about
15% that belong to close binary systems. Here, we shed light on a
puzzling fact: for rotation periods less than 80 days, a red giant
that belongs to a close binary system displays a photometric
modulation about an order of magnitude larger than that of a single
red giant with similar rotational period and physical properties. We
investigate whether binarity leads to larger magnetic fields when
tides lock systems, or if a different spot distribution on single
versus close binary stars can explain this fact. For this, we measure
the chromospheric emission in the CaII H and K lines of 3130 of the
4465 stars studied in a previous work thanks to the LAMOST survey. We
show that red giants in a close-binary configuration with spin-orbit
resonance display significantly larger chromospheric emission than
single stars, suggesting that tidal locking leads to larger magnetic
fields at a fixed rotational period. Beyond bringing interesting new
observables to study the evolution of binary systems, this result
could be used to distinguish single versus binary red giants in
automatic pipelines based on machine learning.
Description:
S-index and associated uncertainties of the stars analysed in the
paper. Each star is identified with its KIC number (Kepler Input
Catalog, Cat. V/133).
The S-index was measured for 3130 red giant stars analysed by Gaulme
et al. (2020, Cat. J/A+A/639/A63).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 20 3130 S-index and associated uncertainties
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
J/A+A/639/A63 : Active red giants asteroseismic + rotation parameters
(Gaulme+, 2020)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 I8 --- KIC KIC number
10- 14 F5.3 --- SCaII S-index
16- 20 F5.3 --- e_SCaII Uncertainty on the S-index
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Acknowledgements:
Charlotte Gehan, gehan(at)mps.mpg.de
(End) Charlotte Gehan [MPS], Patricia Vannier [CDS] 02-Nov-2022