J/A+A/645/A85 Age dissection of the Milky Way discs (Miglio+, 2021)
Age dissection of the Milky Way discs: Red giants in the Kepler field.
Miglio A., Chiappini C., Mackereth T., Davies G., Brogaard K.,
Casagrande L., Chaplin B., Girardi L., Kawata D., Khan S., Izzard R.,
Montalban J., Mosser B., Vincenzo F., Bossini D., Noels A., Rodrigues T.,
Valentini M., Mandel I.
<Astron. Astrophys. 645, A85 (2021)>
=2021A&A...645A..85M 2021A&A...645A..85M (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, late-type ; Stars, ages ; Stars, masses ;
Stars, distances
Keywords: Galaxy: evolution - Galaxy: stellar content - Galaxy: structure -
stars: late-type - stars: mass-loss - asteroseismology
Abstract:
Ensemble studies of red-giant stars with exquisite asteroseismic
(Kepler), spectroscopic (APOGEE), and astrometric (Gaia) constraints
offer a novel opportunity to recast and address long-standing
questions concerning the evolution of stars and of the Galaxy.
Here, we infer masses and ages for nearly 5400 giants with available
Kepler light curves and APOGEE spectra using the code PARAM,
and discuss some of the systematics that may affect the accuracy of
the inferred stellar properties. We then present patterns in mass,
evolutionary state, age, chemical abundance, and orbital parameters
that we deem robust against the systematic uncertainties explored.
First, we look at age-chemical-abundances ([Fe/H] and [alpha/Fe])
relations. We find a dearth of young, metal-rich ([Fe/H]>0.2) stars,
and the existence of a significant population of old (8-9Gyr),
low-[alpha/Fe], super-solar metallicity stars, reminiscent of the age
and metallicity of the well-studied open cluster NGC 6791. The
age-chemo-kinematic properties of these stars indicate that efficient
radial migration happens in the thin disc.
We find that ages and masses of the nearly 400 alpha-element-rich
red-giant-branch (RGB) stars in our sample are compatible with those
of an old (∼11Gyr), nearly coeval, chemical-thick disc population.
Using a statistical model, we show that the width of the observed age
distribution is dominated by the random uncertainties on age, and that
the spread of the inferred intrinsic age distribution is such that 95%
of the population was born within ∼1.5Gyr. Moreover, we find a
difference in the vertical velocity dispersion between low- and
high-[alpha/Fe] populations. This discontinuity, together with the
chemical one in the [alpha/Fe] versus [Fe/H] diagram, and with the
inferred age distributions, not only confirms the different
chemo-dynamical histories of the chemical-thick and thin discs, but it
is also suggestive of a halt in the star formation (quenching) after
the formation of the chemical-thick disc. We then exploit the almost
coeval alpha-rich population to gain insight into processes that may
have altered the mass of a star along its evolution, which are key to
improving the mapping of the current, observed, stellar mass to the
initial mass and thus to the age. Comparing the mass distribution of
stars on the lower RGB (R<11R☉) with those in the red clump
(RC), we find evidence for a mean integrated RGB mass loss
DM=0.10±0.02M☉. Finally, we find that the occurrence of
massive (M≳1.1M☉) alpha-rich stars is of the order of 5% on the
RGB, and significantly higher in the RC, supporting the scenario in
which most of these stars had undergone an interaction with a
companion.
Description:
The data relative to the sample of stars defined in Sec. 4.
Photometric and spectroscopic constraints are taken from 2MASS
(Skrutskie et al., 2006AJ....131.1163S 2006AJ....131.1163S, Cat. VII/233 and APOGEE DR14
(Abolfathi et al., 2018ApJS..235...42A 2018ApJS..235...42A). Orbital parameters are
computed as described in Sec. 2.2. Ages, masses, radii, distances and
extinction are inferred using PARAM's modelling run R1 (see Table 1).
As described in the main paper, we defined a sample with robust age
estimates by removing stars in the RC with masses below 1.2M☉,
because their actual masses are expected to be more significantly
affected by mass loss. Also, among the non core-He burning giants, we
restrict the sample to stars with estimated radii smaller than
11R☉. This avoids contamination by early-AGB stars, and removes
stars with relatively low νmax, a domain where seismic inferences
have not been extensively tested so far. All relevant columns are
accompanied by an associated uncertainty, defined either as the
standard deviation or the 16th and 84th percentiles. Uncertainties are
found in accompanying columns labelled with the suffix 'e_'.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 262 3315 Catalog
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 20 A20 --- APOGEE APOGEE ID in DR14 (2MHHMMSSss+DDMMSSs)
22- 29 I8 --- KIC Kepler Input Catalogue ID
31- 36 F6.3 mag Jmag 2MASS J-band magnitude
38- 43 F6.3 mag Hmag 2MASS H-band magnitude
45- 50 F6.3 mag Ksmag 2MASS Ks-band magnitude
52- 59 F8.4 deg RAdeg Right Ascension (J2000)
61- 67 F7.4 deg DEdeg Declination (J2000)
69- 73 F5.2 --- [Fe/H] APOGEE [Fe/H] (DR14)
75- 79 F5.2 --- [alpha/M] APOGEE [alpha/M] (DR14)
81- 84 F4.1 Gyr Age ? Age from PARAM (R1)
86- 89 F4.1 Gyr b_Age ? Age 18th percentile
91- 94 F4.1 Gyr B_Age ? Age 84th percentile
96- 99 F4.2 Msun Mass Mass from PARAM (R1)
101-104 F4.2 Msun b_Mass Mass 18th percentile
106-109 F4.2 Msun B_Mass Mass 84th percentile
111-115 F5.2 Rsun Rad Radius from PARAM (R1)
117-121 F5.2 Rsun b_Rad Radius 18th percentile
123-127 F5.2 Rsun B_Rad Radius 84th percentile
129-134 F6.3 kpc Dist ?=-0.1 Distance from PARAM (R1)
136-141 F6.3 kpc b_Dist ?=-0.1 Distance 18th percentile
143-148 F6.3 kpc B_Dist ?=-0.1 Distance 84th percentile
150-155 F6.2 mag Av ?=-99.90 Extinction from PARAM (R1)
157-162 F6.2 mag b_Av ?=-99.90 Extinction 18th percentile
164-169 F6.2 mag B_Av ?=-99.90 Extinction 84th percentile
171 I1 --- evstate [1/2] Evolutionary state from
Yu et al. (2018, Cat. J/ApJS/236/42) (1)
173-177 F5.3 kpc zmax Maximum vertical excursion in MWPotential2014
179-183 F5.3 kpc e_zmax Maximum vertical excursion: 1 sigma error
185-189 F5.3 --- Ecc Orbit eccentricity in MWPotential2014
191-195 F5.3 --- e_Ecc Orbit eccentricity: 1 sigma error
197-201 F5.3 kpc Rperi Pericentre radius in MWPotential2014
203-207 F5.3 kpc e_Rperi Pericentre radius: 1 sigma error
209-214 F6.3 kpc Rap Apocentre radius in MWPotential2014
216-220 F5.3 kpc e_Rap Apocentre radius: 1 sigma error
222-226 F5.3 kpc GalR Position Galactocentric cylindrical
coordinates: Galactocentric radius
228-233 F6.3 rad Galphi Position: azimuth
235-239 F5.3 kpc GalZ Position: height above the Galactic midplane
241-247 F7.2 km/s vR Galactocentric radial velocity
249-254 F6.2 km/s vT Galactocentric tangential velocity
256-262 F7.2 km/s vZ Galactocentric vertical velocity
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Note (1): Evolutionary state as follows:
1 = RGB
2 = core-He-burning
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Acknowledgements:
Andrea Miglio, a.miglio(at)bham.ac.uk
(End) Patricia Vannier [CDS] 05-Jan-2021