J/A+A/671/A21 Radial-velocity of the young alpha-rich stars (Jofre+, 2023)
Cannibals in the thick disk.
II. Radial-velocity monitoring of the young alpha-rich stars.
Jofre P., Jorissen A., Aguilera-Gomez C., Van Eck S., Tayar J.,
Pinsonneault M., Zinn J., Goriely S., Van Winckel H.
<Astron. Astrophys. 671, A21 (2023)>
=2023A&A...671A..21J 2023A&A...671A..21J (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, giant ; Radial velocities
Keywords: stars: abundances - stars: atmospheres - binaries: close -
stars: evolution - Galaxy: stellar content - Galaxy: evolution
Abstract:
Determining ages of stars for reconstructing the history of the Milky
Way remains one of the most difficult tasks in astrophysics. This
involves knowing when it is possible to relate the stellar mass with
its age and when it is not. The young alpha-rich (YAR) stars present
such a case in which we are still not sure about their ages because
they are relatively massive, implying young ages, but their abundances
are alpha-enhanced, which implies old ages.
We report the results from new observations from a long-term
radial-velocity-monitoring campaign complemented with high-resolution
spectroscopy, as well as new astrometry and seismology of a sample of
41 red giants from the third version of APOKASC, which includes YAR
stars. The aim is to better characterize the YAR stars in terms of
binarity, mass, abundance trends, and kinematic properties.
The radial velocities of HERMES, APOGEE, and Gaia were combined to
determine the binary fraction among YAR stars. In combination with
their mass estimate, evolutionary status, chemical composition, and
kinematic properties, it allowed us to better constrain the nature of
these objects.
We found that stars with M<1M☉ were all single, whereas stars
with M>1M☉ could be either single or binary. This is in
agreement with theoretical predictions of population synthesis models.
Studying their [C/N], [C/Fe], and [N/Fe], trends with mass, it became
clear that many YAR stars do not follow the APOKASC stars, favoring
the scenario that most of them are the product of mass transfer. Our
sample further includes two likely undermassive stars, that is to say
of such as low mass that they cannot have reached the red clump within
the age of the Universe, unless their low mass is the signature of
mass loss in previous evolutionary phases. These stars do not show
signatures of currently being binaries. Both YAR and undermassive
stars might show some anomalous APOGEE abundances for the elements N,
Na, P, K, and Cr; although, higher-resolution optical spectroscopy
might be needed to confirm these findings.
Considering the significant fraction of stars that are formed in pairs
and the variety of ways that makes mass transfer possible, the
diversity in properties in terms of binarity, and chemistry of the YAR
and undermassive stars studied here implies that most of these objects
are likely not young.
Description:
The RV data were obtained with the HERMES spectrograph mounted on the
1.2m Mercator telescope, at the Roque de Los Muchachos Observatory, La
Palma, Canary Islands. The HERMES spectrograph covers the optical
wavelength range from 380 to 900nm with a spectral resolution of about
86000. RVs were derived by cross-correlating the stellar spectrum with
a mask covering the wavelength range 480-650nm and mimicking the
spectrum of Arcturus (K1.5 III). The restricted wavelength span is to
avoid both telluric lines at the red end and the crowded and poorly
exposed blue end of the spectrum.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 102 41 Program stars
tableb3.dat 32 296 Radial velocities
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
III/284 : APOGEE-2 data from DR16 (Johnsson+, 2020)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- Star Star identifier
5- 12 I8 --- KIC KIC identifier
14- 31 A18 --- APOGEE APOGEE identifier
33- 51 I19 --- GaiaDR3 Gaia DR3 identifier
53- 57 F5.2 mag Gmag Gaia G magnitude
59- 63 F5.2 mag Ksmag 2MASS Ks magnitude
65- 68 I4 K Teff Effective temperature
from APOGEE DR16, and APOKASC-3
70- 73 F4.2 [cm/s2] logg Surface gravity
from APOGEE DR16, and APOKASC-3
75- 79 F5.2 [-] [Fe/H] Metallicity from APOGEE DR16, and APOKASC-3
81- 84 F4.2 [-] [alpha/Fe] Abundance [alpha/Fe]
from APOGEE DR16, and APOKASC-3
86- 90 F5.2 [-] [C/N] Abundance [C/N]
from APOGEE DR16, and APOKASC-3
92- 95 F4.2 Msun M Mass
97-100 F4.2 Msun e_M Mass error
102 I1 --- Evol Evolutionary stage of the stars (1)
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Note (1): Evolutionary stage, as derived from APOKASC-3, as follows:
1 = red giant branch
2 = red clump
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Byte-by-byte Description of file: tableb3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- KIC KIC number
10- 24 F15.7 d HJD Heliocentric Julain date
26- 32 F7.2 km/s RV Radial velocity
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Acknowledgements:
Paola Jofre, paula.jofre(at)mail.udp.cl
References:
Jofre et al., Paper I 2016A&A...595A..60J 2016A&A...595A..60J
(End) Patricia Vannier [CDS] 22-Jan-2023