J/other/Nat/603.599 247014 subgiant stars data (Xiang+, 2022)
A time-resolved picture of our Milky Way's early formation history.
Xiang M., Rix H.-W.
<Nature, 603, 599-603 (2022)>
=2022Natur.603..599X 2022Natur.603..599X (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, giant ; Optical ; Stars, ages
Abstract:
The formation of our Milky Way can be split up qualitatively into
different phases that resulted in its structurally different stellar
populations: the halo and the disk components. Revealing a
quantitative overall picture of our Galaxy's assembly requires a large
sample of stars with very precise ages. Here we report an analysis of
such a sample using subgiant stars. We find that the stellar
age-metallicity distribution p(τ, [Fe/H]) splits into two almost
disjoint parts, separated at age τ~=8Gyr. The younger part
reflects a late phase of dynamically quiescent Galactic disk formation
with manifest evidence for stellar radial orbit migration4; the other
part reflects the earlier phase, when the stellar halo and the old
α-process-enhanced (thick) disk formed. Our results indicate
that the formation of the Galaxy's old (thick) disk started
approximately 13Gyr ago, only 0.8Gyr after the Big Bang, and 2Gyr
earlier than the final assembly of the inner Galactic halo. Most of
these stars formed around 11Gyr ago, when the Gaia-Sausage-Enceladus
satellite merged with our Galaxy. Over the next 5-6Gyr, the Galaxy
experienced continuous chemical element enrichment, ultimately by a
factor of 10, while the star-forming gas managed to stay well mixed.
Description:
With the recent data release (eDR3) of the Gaia mission (Cat. I/350)
and the recent data release (DR7) of the LAMOST spectroscopic survey
(http://dr7.lamost.org/catalogue), we identify a set of approximately
250000 subgiant stars based on their position in the effective
temperatures (Teff)-absolute magnitude (MK) diagram. The ages ({atau})
of these subgiant stars are estimated by fitting to the Yonsei-Yale
(YY) stellar isochrones18 with a Bayesian approach, which draws on the
astrometric distances (parallaxes), apparent magnitudes (fluxes),
spectroscopic chemical abundances ([Fe/H], [α/Fe] where α
refers to α elements Mg, Si, Ca, Ti), Teff and MK.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 288 247104 Stellar age, abundance, and orbit action for
247014 subgiant stars from LAMOST DR7 and
Gaia eDR3
--------------------------------------------------------------------------------
See also:
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
http://dr7.lamost.org/catalogue : LAMOST DR7 Home Page
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- Id Sequential number
11- 20 F10.6 deg RAdeg Right ascension (J2000)
25- 34 F10.6 deg DEdeg Declination (J2000)
37- 42 F6.3 Gyr Age Age estimate
46- 50 F5.3 Gyr e_Age Uncertainty in age estimate
53- 58 F6.3 [-] [Fe/H] LAMOST metallicity
62- 66 F5.3 [-] e_[Fe/H] Uncertainty in [Fe/H]
70- 77 F8.2 kpc.km/s JR Orbital radial action
81- 88 F8.2 kpc.km/s JPHI Orbital azimuthal action
92- 99 F8.2 kpc.km/s JZ Orbital vertical action
104-109 F6.3 kpc X X value in Galactic rectangular
coordinate, positive to anti-center
113-119 F7.3 kpc Y Y value in Galactic rectangular coordinate
123-129 F7.3 kpc Z Z value in Galactic rectangular
coordinate, positive to north pole
134-152 I19 --- GaiaEDR3 Gaia eDR3 source id
(missing last digit !!!)
157-192 A36 --- LAMOST LAMOST spectral id, in format of
obsdate-planid-spectrograph-fiber
196-200 F5.1 --- S/Ng LAMOST spectral S/N in SDSS g band
203-208 F6.1 K Teff LAMOST effective temperature
212-216 F5.1 K e_Teff Uncertainty in Teff
221-225 F5.3 [cm/s2] logg LAMOST surface gravity derived
230-234 F5.3 [cm/s2] e_logg Uncertainty in logg
237-243 F7.3 mag MKspec Spectroscopic absolute magnitude in
2MASS Ks band
248-252 F5.3 mag e_MKspec Uncertainty in MKspec
257-261 F5.3 mag MKcomb Spectroscopic & geometric combined
absolute magnitude in 2MASS Ks band
264-270 F7.3 mag e_MKcomb Uncertainty in MKcomb
274-279 F6.3 --- [alpha/Fe] ?=- LAMOST alpha-to-iron abundance ratio
284-288 F5.3 --- e_[alpha/Fe] ?=- Uncertainty in [alpha/Fe]
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 19-Jun-2023