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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/222474
Spectroscopic age estimates for APOGEE red-giant stars: Precise spatial and kinematic trends with age in the Galactic disc
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Over the last few years, many studies have found an empirical relationship between the abundance of a star and its age. Here we
estimate spectroscopic stellar ages for 178 825 red-giant stars observed by the APOGEE survey with a median statistical uncertainty
of 17%. To this end, we use the supervised machine learning technique XGBoost, trained on a high-quality dataset of 3060 redgiant and red-clump stars with asteroseismic ages observed by both APOGEE and Kepler. After verifying the obtained age estimates
with independent catalogues, we investigate some of the classical chemical, positional, and kinematic relationships of the stars as a
function of their age. We find a very clear imprint of the outer-disc flare in the age maps and confirm the recently found split in the
local age-metallicity relation. We present new and precise measurements of the Galactic radial metallicity gradient in small age bins
between 0.5 and 12 Gyr, confirming a steeper metallicity gradient for ∼2−5 Gyr old populations and a subsequent flattening for older
populations mostly produced by radial migration. In addition, we analyse the dispersion about the abundance gradient as a function
of age. We find a clear power-law trend (with an exponent β ≈ 0.15) for this relation, indicating a relatively smooth radial migration
history in the Galactic disc over the past 7−9 Gyr. Departures from this power law may possibly be related to the Gaia Enceladus
merger and passages of the Sagittarius dSph galaxy. Finally, we confirm previous measurements showing a steepening in the agevelocity dispersion relation at around ∼9 Gyr, but now extending it over a large extent of the Galactic disc (5 kpc < RGal < 13 kpc). To
establish whether this steepening is the imprint of a Galactic merger event, however, detailed forward modelling work of our data is
necessary. Our catalogue of precise stellar ages and the source code to create it are publicly available.
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ANDERS, Friedrich, GISPERT, P., RATCLIFFE, Bridget, CHIAPPINI, C., MINCHEV, I., NEPAL, Samir, QUEIROZ, A. b. a., AMARANTE, João antônio silveira do, ANTOJA CASTELLTORT, M. teresa, CASALI, Giada, CASAMIQUELA, L., KHALATYAN, A., MIGLIO, A., PEROTTONI, Helio, SCHULTHEIS, M.. Spectroscopic age estimates for APOGEE red-giant stars: Precise spatial and kinematic trends with age in the Galactic disc. _Astronomy & Astrophysics_. 2023. Vol. 678. [consulta: 25 de novembre de 2025]. ISSN: 0004-6361. [Disponible a: https://hdl.handle.net/2445/222474]