J/MNRAS/476/5216 Thick disc probability of GALAH stars (Duong+, 2018)
The GALAH survey: properties of the Galactic disc(s) in the solar neighbourhood.
Duong L., Freeman K.C., Asplund M., Casagrande L., Buder S., Lind K.,
Ness M., Bland-Hawthorn J., De Silva G.M., D'orazi V., Kos J., Lewis G.F.,
Lin J., Martell S.L., Schlesinger K., Sharma S., Simpson J.D., Zucker D.B.,
Zwitter T., Anguiano B., Da Costa G.S., Hyde E., Horner J., Kafle P.R.,
Nataf D.M., Reid W., Stello D., Ting Y.-S., Wyse R.F.G.
<Mon. Not. R. Astron. Soc., 476, 5216-5232 (2018)>
=2018MNRAS.476.5216D 2018MNRAS.476.5216D (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, nearby ; Optical
Keywords: surveys - stars: abundances - Galaxy: disc - Galaxy: evolution -
Galaxy: formation
Abstract:
Using data from the GALAH pilot survey, we determine properties of the
Galactic thin and thick discs near the solar neighbourhood. The data
cover a small range of Galactocentric radius (7.9≲RGC≲9.5kpc), but
extend up to 4kpc in height from the Galactic plane, and several kpc
in the direction of Galactic anti-rotation (at longitude
260°≤l≤280°). This allows us to reliably measure the
vertical density and abundance profiles of the chemically and
kinematically defined 'thick' and 'thin' discs of the Galaxy. The thin
disc (low-α population) exhibits a steep negative vertical
metallicity gradient, at d[M/H]/dz=-0.18±0.01dex/kpc, which is
broadly consistent with previous studies. In contrast, its vertical
α-abundance profile is almost flat, with a gradient of
d[α/M]/dz=0.008±0.002dex/kpc. The steep vertical metallicity
gradient of the low-α population is in agreement with models
where radial migration has a major role in the evolution of the thin
disc. The thick disc (high-α population) has a weaker vertical
metallicity gradient d[M/H]/dz=-0.058±0.003dex/kpc. The
α-abundance of the thick disc is nearly constant with height,
d[α/M]/dz=0.007±0.002dex/kpc. The negative gradient in
metallicity and the small gradient in [α/M] indicate that the
high-α population experienced a settling phase, but also formed
prior to the onset of major Type Ia supernova enrichment. We explore
the implications of the distinct α-enrichments and narrow
[α/M] range of the sub-populations in the context of thick disc
formation.
Description:
We present a data table listing the stars analysed in this work, their
GALAH object ID, UCAC4 catalogue ID, coordinates, thick disc
membership probability and distances.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 60 3191 Stars analysed in this work
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See also:
I/322 : UCAC4 Catalogue (Zacharias+, 2012)
J/MNRAS/478/4513 : GALAH Survey DR2 (Buder+, 2018)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 15 I15 --- GALAH Unique identifier for each GALAH observation
of an object (1)
17- 26 A10 --- UCAC4 Identifer in the UCAC4 catalogue
28- 35 F8.4 deg RAdeg Right ascension (J2000)
37- 44 F8.4 deg DEdeg Declination (J2000)
46- 53 F8.2 pc Dist Distance
55- 60 F6.4 --- Pr(thick) [0/1] Normalised thick disk membership
probability (2)
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Note (1): If the same object is observed multiple times, it will have multiple
object IDs.
Note (2): High values indicate likely membership. Normalised such that
Pr(thin)=1-Pr(thick).
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 04-May-2021