J/ApJ/900/4 Abundances and ages of stars in the Milky Way bulge (Sit+, 2020)
The Age Distribution of Stars in the Milky Way Bulge.
Sit T., Ness M.K.
<Astrophys. J., 900, 4 (2020)>
=2020ApJ...900....4S 2020ApJ...900....4S
ADC_Keywords: Stars, ages; Abundances, [Fe/H]; Galactic center; Milky Way;
Effective temperatures; Infrared
Keywords: Galactic bulge ; Milky Way Galaxy ; Stellar ages ;
Stellar properties ; Stellar abundances
Abstract:
The age and chemical characteristics of the Galactic bulge link to the
formation and evolutionary history of the Galaxy. Data-driven methods
and large surveys enable stellar ages and precision chemical
abundances to be determined for vast regions of the Milky Way,
including the bulge. Here, we use the data-driven approach of The
Cannon, to infer the ages and abundances for 125367 stars in the Milky
Way, using spectra from Apache Point Observatory Galaxy Evolution
Experiment (apogee) DR14. We examine the ages and metallicities of
1654 bulge stars within RGAL<3.5kpc. We focus on fields with
b<12°, and out to longitudes of l<15°. We see that stars in
the bulge are about twice as old (τ=8Gyr), on average, compared to
those in the solar neighborhood (τ=4Gyr), with a larger dispersion
in [Fe/H] (∼0.38 compared to 0.23dex). This age gradient comes
primarily from the low-α stars. Looking along the Galactic
plane, the very central field in the bulge shows by far the largest
dispersion in [Fe/H] (σ[Fe/H]∼0.4dex) and line-of- sight
velocity (σvr∼90km/s), and simultaneously the smallest
dispersion in age. Moving out in longitude, the stars become
kinematically colder and less dispersed in [Fe/H], but show a much
broader range of ages. We see a signature of the X-shape within the
bulge at a latitude of b=8°, but not at b=12°. Future apogee
and other survey data, with larger sampling, affords the opportunity
to extend our approach and study in more detail, to place stronger
constraints on models of the Milky Way.
Description:
We have used the data-driven approach of The Cannon
(Ness+, 2015, J/ApJ/808/16) to obtain ages and abundances for 125367
apogee stars. We provide the catalog of these here and undertake an
analysis of the 2567 stars within the bulge region of <3.5kpc.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 250 125367 Table of results
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See also:
III/284 : APOGEE-2 data from DR16 (Johnsson+, 2020)
J/ApJ/721/L28 : Red clump stars in Galactic Bulge from OGLE-III (Nataf+, 2010)
J/A+A/512/A41 : Abundances of microlensed stars in the Bulge (Bensby+, 2010)
J/A+A/549/A147 : Abundances of microlensed bulge dwarf stars. V. (Bensby+,2013)
J/ApJ/808/16 : The Cannon: new approach to determine abundances (Ness+,2015)
J/AJ/151/144 : ASPCAP weights for 15 APOGEE chemical elements (Garcia+,2016)
J/ApJ/836/5 : Abundances of LAMOST giants from APOGEE DR12 (Ho+, 2017)
J/A+A/605/A89 : Abundances of microlensed Bulge dwarf stars VI. (Bensby+,2017)
J/ApJ/865/68 : Abundances for 79 Sun-like stars within 100pc (Bedell+, 2018)
J/ApJS/239/32 : APOKASC-2 catalog of Kepler evolved stars (Pinsonneault+,2018)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- ID 2MASS position based identifier
20- 23 A4 --- alpha alpha: high or low (1)
25- 35 F11.2 K Teff [-2419915/5663] Effective temperature from The
Cannon
37- 41 F5.2 K e_Teff [0.9/31]? Uncertainty in Teff
43- 51 F9.3 [cm/s2] logg [-4159/4.47] log Surface Gravity from The
Cannon
53- 57 F5.3 [cm/s2] e_logg [0.004/0.08]? Uncertainty in logg
59- 67 F9.3 [-] [Fe/H] [-2848/0.79] Abundance, [Fe/H] from The Cannon
69- 73 F5.3 [-] e_[Fe/H] [0.001/0.03]? Uncertainty in [Fe/H]
75- 82 F8.3 [-] [C/Fe] [-790/0.78] Abundance, [C/Fe] from The Cannon
84- 88 F5.3 [-] e_[C/Fe] [0.002/0.04]? Uncertainty in [C/Fe]
90- 98 F9.3 [-] [N/Fe] [-1160/1.53] Abundance, [N/Fe] from The Cannon
100-104 F5.3 [-] e_[N/Fe] [0.002/0.04]? Uncertainty in [N/Fe]
106-113 F8.3 [-] [O/Fe] [-817/0.51] Abundance, [O/Fe] from The Cannon
115-119 F5.3 [-] e_[O/Fe] [0.001/0.03]? Uncertainty in [O/Fe]
121-128 F8.3 [-] [Mg/Fe] [-668/0.49] Abundance, [Mg/Fe] from The Cannon
130-134 F5.3 [-] e_[Mg/Fe] [0.001/0.02]? Uncertainty in [Mg/Fe]
136-144 F9.3 [-] [Al/Fe] [-1051/0.86] Abundance [Al/Fe] from The Cannon
146-150 F5.3 [-] e_[Al/Fe] [0.001/0.04]? Uncertainty in [Al/Fe]
152-159 F8.3 [-] [Si/Fe] [-782/0.39] Abundance, [Si/Fe] from The Cannon
161-165 F5.3 [-] e_[Si/Fe] [0.001/0.02]? Uncertainty in [Si/Fe]
167-174 F8.3 [-] [K/Fe] [-930/0.79]? Abundance, [K/Fe] from The Cannon
(1)
176-180 F5.3 [-] e_[K/Fe] [0.001/0.03]? Uncertainty in [K/Fe] (1)
182-189 F8.3 [-] [Ca/Fe] [-587/0.38] Abundance, [Ca/Fe] from The Cannon
191-195 F5.3 [-] e_[Ca/Fe] [0.001/0.02]? Uncertainty in [Ca/Fe]
197-204 F8.3 [-] [Mn/Fe] [-942/0.5] Abundance, [Mn/Fe] from The Cannon
206-210 F5.3 [-] e_[Mn/Fe] [0.001/0.02]? Uncertainty in [Mn/Fe]
212-220 F9.3 [Myr] Age [-3020/5.88] log, Age from The Cannon
222-226 F5.3 [Myr] e_Age [0.004/0.2]? Uncertainty in logage
228-250 F23.2 --- Chi2 [966/6.2e+19] χ2 of the fit
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Note (1): High- and low-alpha results are found in one table, differentiated by
the column alpha, and the fact that the low-alpha results have null values
for [K/Fe].
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 26-Oct-2021