J/A+A/673/A18 Old Galactic stellar populations (Giribaldi+, 2023)
Chronology of the chemical enrichment of the old Galactic stellar populations.
Giribaldi R.E., Smiljanic R.
<Astron. Astrophys. 673, A18 (2023)>
=2023A&A...673A..18G 2023A&A...673A..18G (SIMBAD/NED BibCode)
ADC_Keywords: Stars, nearby ; Stars, late-type ; Stars, ages
Keywords: standards - surveys - stars: atmospheres -
stars: fundamental parameters - stars: late-type
Abstract:
Over its history, the Milky Way has accreted several smaller satellite
galaxies. These mergers added stars and gas to the Galaxy and affected
the properties of the pre-existing stellar populations. Stellar
chemical abundances and ages are needed to establish the chronological
order of events that occur before, during, and after such mergers.
We report the precise ages (∼6.5%) and chemical abundances for the
Titans, a sample of old metal-poor dwarfs and subgiants with accurate
atmospheric parameters. We also obtain their ages with an average
precision of 10% for a selected sample of dwarf stars from the GALAH
survey. We use these stars, located within ∼1 kiloparsec of the Sun,
to analyse the chronology of the chemical evolution of in situ and
accreted metal-poor stellar populations.
We determined ages via isochrone fitting. For the Titans, we
determined abundances of Mg, Si, Ca, Ti, Ni, Ba, and Eu using spectrum
synthesis. The [Mg/Fe] abundances of the GALAH stars were re-scaled to
be consistent with the abundances of the Titans. We separated stellar
populations by primarily employing chemical abundances and orbits.
We find that star formation in the so-called Gaia-Enceladus or
Gaia-Sausage galaxy, the last major system to merge with the Milky
Way, lasted at least 3 billion years and got truncated 9.6±0.2
billion years ago. This marks with a very high level of precision the
last stage of its merging process. We also identified stars of a
heated metal-poor in-situ population with virtually null net rotation,
probably disturbed by several of the early Milky Way mergers. We show
that this population is more metal-rich than Gaia-Enceladus at any
moment in time.
The sequence of events uncovered in our analysis supports the
hypothesis that Gaia-Enceladus truncated the formation of the
high-α disc and caused the gas infall that forms the low-α
disc. This finding is in agreement with theoretical predictions.
Description:
The spectroscopic data used to determine the atmospheric parameters
and abundances of the Titans are described in Giribaldi et al. (2021).
We present the data produced in this paper used for the discussion.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
titans.dat 241 48 Titans parameter set ADS (complements the table
J/A+A/650/A194/table2)
select.dat 83 233 Selected stars
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See also:
J/MNRAS/506/150 : The GALAH+ Survey DR3 (Buder+, 2021)
J/A+A/650/A194 : Titans metal-poor reference stars. I. (Giribaldi+, 2021)
Byte-by-byte Description of file: titans.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Star Simbad star name
17- 24 F8.4 deg RAdeg Right ascension (ICRS, epoch J2000)
26- 33 F8.4 deg DEdeg Declination (ICRS, epoch J2000)
35- 39 F5.2 mag Vmag Visual magnitude in Johnson system
41- 49 F9.3 mas/yr pmRA Proper motion in right ascension
(ICRS, epoch J2000) form Gaia DR3
51- 59 F9.3 mas/yr pmDE Proper motion in declination
(ICRS, epoch J2000) form Gaia DR3
61- 66 F6.3 mas Plx Gaia DR3 parallax
68- 72 F5.3 mas e_Plx Gaia DR3 parallax error
74- 80 F7.2 km/s HV Heliocentric velocity
82- 85 F4.2 km/s e_HV Heliocentric velocity error
87- 91 F5.2 --- [Ti/Fe] Titanium to iron ratio relative to the Sun
93- 96 F4.2 --- [Mg/Fe] Magnesium to iron ratio relative to the Sun
98-101 F4.2 --- e_[Mg/Fe] Magnesium to iron ratio error
103-111 F9.2 --- [Si/Fe] ?=-99999 Silicon to iron ratio
relative to the Sun
113-121 F9.2 --- [Ca/Fe] ?=-99999 Calcium to iron ratio
relative to the Sun
123-131 F9.2 --- [Ni/Fe] ?=-99999 Nickel to iron ratio
relative to the Sun
133-141 F9.2 --- [Eu/Fe] ?=-99999 Europium to iron ratio
relative to the Sun
143-151 F9.2 --- [Ba/Fe] ?=-99999 Barium to iron ratio
relative to the Sun
153-161 F9.2 --- e_[Ba/Fe] ?=-99999 Barium to iron ratio error
163-166 F4.2 --- diffCor Difussion correction
168-171 F4.1 Gyr Age Most probable age
173-176 F4.1 Gyr b_Age Age at lower 1 sigma limit
178-181 F4.1 Gyr B_Age Age at upper 1 sigma limit
183-187 F5.3 Msun Mass Most probable mass
189-193 F5.3 Msun b_Mass Mass at lower 1 sigma limit
195-199 F5.3 Msun B_Mass Mass at upper 1 sigma limit
201-205 F5.3 Rsun R Most probable radius
207-211 F5.3 Rsun b_R Radius at lower 1 sigma limit
213-217 F5.3 Rsun B_R Radius at upper 1 sigma limit
219-225 F7.4 mag Gmag Gaia G magnitude
227-233 F7.4 mag BPmag Gaia Bp magnitude
235-241 F7.4 mag RPmag Gaia Rp magnitude
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Byte-by-byte Description of file: select.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Star Star name (1)
17- 35 I19 --- GaiaDR2 Gaia DR2 identifier
37- 40 I4 K Teff Effective temperature
42- 45 F4.2 [cm/s2] logg Surface gravity
47- 50 F4.1 Gyr Age Stellar age
52- 54 F3.1 Gyr e_Age 1 sigma error towards lower age
56- 58 F3.1 Gyr E_Age 1 sigma error towards higher age
60- 64 F5.2 [-] [Fe/H] Metallicity or iron to hydrogen ratio
66- 70 F5.2 [-] [Mg/Fe] Magnesium to iron ratio relative to the Sun
72- 83 A12 --- Pop Membership ascription to a Galactic
population in the halo
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Note (1): Simbad names are given for Titans stars, whereas GALAH identifiers
are given for stars in the GALAH survey.
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Acknowledgements:
Riano Escate Giribaldi, rianoesc(at)gmail.com
(End) Patricia Vannier [CDS] 20-Apr-2023