title: NLTE analysis of the Gaia-ESO spectroscopic survey.
creator: Kovalev, Mikhail
subject: 520
subject: 520 Astronomy and allied sciences
description: In this work, we develop the spectral analysis pipeline that combines the NLTE synthetic spectra withthe Payne spectral model (Ting et al.2018).  We compute two spectral grids, one grid with all elements treated in LTE and a second grid with iron, magnesium, titanium and manganese modelled in NLTE, to study the NLTE effects on the determination of the stellar parameters and chemical abundances.    This pipeline is applied to spectra from the third public data release of the Gaia-ESO (Gilmore et al. 2012).  We validate the method on the subsample of standard stars and cluster’s members and find significant differences between NLTE and LTE in the metal-poor regime.  All clusters are homogeneous in Fe and Ti, but several globular clusters showed significant dispersion in [Mg/Fe].  The depletion of the mean [Mg/Fe] in several globular clusters, compared to field stars of the same metallicity, may indicate their ex-situ formation history. We also combine our NLTE results with Gaia DR2 (Gaia Collaboration et al.2018) astrometric data to study Galactic chemo-dynamic evolution.  We apply chemical separation to select high-[α/Fe] and low-[α/Fe] disk populations,  with halo stars selected using kinematics.  We confirm previous results like super-solar Mg  abundance  in  the  metal-poor  regime  and  decrease  of  [Mg/Fe]  to  the  solar abundances in the metal-rich regime.  We find a constant NLTE [Mg/Fe]∼0.3 dex ratio for both metal-poor disk and halo with relatively small star-to-star scatter. The halo stars with solar-like [Mg/Fe] are probably accreted from the other galaxies. The observed eccentricity distribution for high-[α/Fe] disk population rules out a violent thick disk formation mechanisms like direct accretion and dynamic heating. The measured chemical and kinematic gradients and velocity dispersions of the high-[α/Fe] population can be explained by the gas-rich merger scenario with thenon-negligible contribution from the radial migration.
date: 2019
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/27411/1/thesis_Mikhail_Kovalev.pdf
identifier: DOI:10.11588/heidok.00027411
identifier: urn:nbn:de:bsz:16-heidok-274114
identifier:   Kovalev, Mikhail  (2019) NLTE analysis of the Gaia-ESO spectroscopic survey.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/27411/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng