J/A+A/683/A111 Young alpha-rich stars in the Galaxy from K2 (Grisoni+, 2024)
K2 results for "young" alpha-rich stars in the Galaxy.
Grisoni V., Chiappini C., Miglio A., Brogaard K., Casali G., Willett E.,
Montalban J., Stokholm A., Thomsen J.S., Tailo M., Matteuzzi M.,
Valentini M., Elsworth Y., Mosser B.
<Astron. Astrophys. 683, A111 (2024)>
=2024A&A...683A.111G 2024A&A...683A.111G (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, late-type ; Optical
Keywords: asteroseismology - stars: late-type - Galaxy: abundances -
Galaxy: evolution - Galaxy: formation
Abstract:
The origin of apparently young α-rich stars in the Galaxy is
still a matter of debate in Galactic archaeology, whether they are
genuinely young or might be products of binary evolution, and mergers
or mass accretion.
Our aim is to shed light on the nature of young α-rich stars in
the Milky Way by studying their distribution in the Galaxy thanks to
an unprecedented sample of giant stars that cover different Galactic
regions and have precise asteroseismic ages, and chemical and
kinematic measurements.
We analyzed a new sample of ∼6000 stars with precise ages coming from
asteroseismology. Our sample combines the global asteroseismic
parameters measured from light curves obtained by the K2 mission with
stellar parameters and chemical abundances obtained from APOGEE DR17
and GALAH DR3, then cross-matched with Gaia DR3. We define our sample
of young α-rich stars and study their chemical, kinematic, and
age properties.
We investigated young α-rich stars in different parts of the
Galaxy and we find that the fraction of young α-rich stars
remains constant with respect to the number of high-α stars at
∼10%. Furthermore, young α-rich stars have kinematic and
chemical properties similar to high-α stars, except for [C/N]
ratios.
Thanks to our new K2 sample, we conclude that young α-rich stars
have similar occurrence rates in different parts of the Galaxy, and
that they share properties similar to the normal high-α
population, except for [C/N] ratios. This suggests that these stars
are not genuinely young, but are products of binary evolution, and
mergers or mass accretion. Under that assumption, we find the fraction
of these stars in the field to be similar to that found recently in
clusters. This suggests that ∼10% of the low-α field stars could
also have their ages underestimated by asteroseismology. This should
be kept in mind when using asteroseismic ages to interpret results in
Galactic archaeology.
Description:
Our observational sample combines the global asteroseismic parameters
measured from light curves obtained with the K2 mission (Howell et
al., 2014PASP..126..398H 2014PASP..126..398H, Cat. IV/34) with chemical abundances
inferred from high-resolution spectra taken by the APOGEE DR17 survey
(Abdurro'uf et al., 2022ApJS..259...35A 2022ApJS..259...35A, Cat. III/286) and also GALAH
DR3 (Buder et al., 2021MNRAS.506..150B 2021MNRAS.506..150B, Cat. J/MNRAS/506/150), and
astrometric information from the third data release of Gaia (Gaia DR3,
Gaia Collaboration, 2023A&A...674A...1G 2023A&A...674A...1G, Cat. I/355).
In Table A.1, we show the list of IDs for the best-candidate young
alpha-rich stars present in both samples studied in our paper. In
the first column, we report the K2 ID with the corresponding campaign.
All the asteroseismic, spectroscopic, and astrometric information will
then be released together with the catalogue paper (Willett et al. in
prep.).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 18 104 List of IDs for the best-candidate young
alpha-rich stars present in both samples
studied in our paper
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See also:
IV/34 : K2 Ecliptic Plane Input Catalog (EPIC) (Huber+, 2017)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- Name Name, K2 ID with the corresponding campaign
(KTWONNNNNNNNN-CNNN)
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Acknowledgements:
Valeria Grison, valeria.grisoni(at)inaf.it
(End) Patricia Vannier [CDS] 27-Dec-2023