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Stellar spectroscopy is a powerful tool for analysing everything from the physics of stars to the evolution of galaxies. Dark absorption lines in the light received here on Earth offer direct insight into physical processes in the stars themselves, as they uniquely reflect the atomic structure of the elements present. These lines can be used to yield useful information about the stellar atmosphere, such as its temperature, density, and chemical composition, representing the abundance of the elements in the star. Furthermore, we can use abundance information in stars to trace the formation of elements and differentiate between separate nucleosynthesis paths. A good understanding of the formation process within stars during their lives and explosive deaths can, in turn, help us better understand the creation of galactic structures. The inference of stellar abundances requires a physical model of the stellar atmosphere, and only by accurately modelling the interactions between photons and matter can we measure the abundance of the element that causes the spectral line. However, we are often held back by simplistic assumptions to reduce the complexity of the model which, in the past, has been a necessity. However, with the advancement in computational power, these assumptions can be removed. First, local thermodynamic equilibrium (LTE) is a common simplification that is only valid in deeper layers of stars at higher densities. Second, it is often assumed that the atmospheres of solar-like stars are hydrostatic and can be represented by one-dimensional (1D) models, instead of running expensive three-dimensional (3D) hydrodynamic simulations. Both simplifications cause incorrect predictions of observed strengths and shapes of spectral lines. I illustrate the impact of moving from LTE to non-LTE by replacing Saha-Boltzmann equations with statistical equilibrium calculations, producing a significant impact on titanium, a key galactic evolution tracer due to both its number

© ESO, 2015. Artículo firmado por 29 autores. We are grateful to the anonymous referee for constructive comments and suggestions. R. A. Marino is funded by the Spanish program of International Campus of Excellence Moncloa (CEI). This study makes uses of the data provided by the Calar Alto Legacy Integral Field Area (CALIFA) survey (http://www.califa.caha.es). CALIFA is the first legacy survey being performed at Calar Alto. The CALIFA collaboration would like to thank the IAA-CSIC and MPIA-MPG as major partners of the observatory, and CAHA itself, for the unique access to telescope time and support in manpower and infrastructures. The CALIFA collaboration thanks also the CAHA staff for their dedication to this project. We thank Carmen Eliche Moral and Antonio Cava for stimulating discussions at several points in the developments of this work. We acknowledge support from the Plan Nacional de Investigación y Desarrollo funding programs, AyA2010-15081, AyA2012-30717 and AyA2013-46724P, of Spanish Ministerio de Economía y Competitividad (MINECO). A.G.d.P. acknowledges the support from the FP7 Marie Curie Actions of the European Commission, via the Initial Training Network DAGAL under REA grant agreement PITN-GA-2011-289313. C.C.-T. thanks the support of the Spanish Ministerio de Educación, Cultura y Deporte by means of the FPU fellowship program. C.J.W. acknowledges support through the Marie Curie Career Integration Grant 303912. Support for L.G. is provided by the Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC 120009, awarded to The Millennium Institute of Astrophysics, MAS. L.G. acknowledges support by CONIC YT through FONDECYT grant 3140566. S.F.S. thanks the CONACYT-125180 and DGAPA-IA100815 projects for providing him support in this study. J.M.A. acknowledges support from the European Research Council Starting Grant (SEDmorph; P.I. V. Wild). P.P. is supported by FCT through the Investigador FCT Contract No. IF/01220/20, We study, for the first time in a statistically significant and well-defined sample, the relation between the outer-disk ionized-gas metallicity gradients and the presence of breaks in the surface brightness profiles of disk galaxies. Sloan Digital Sky Survey (SDSS) g′- and r′-band surface brightness, (g′ – r′) color, and ionized-gasoxygen abundance profiles for 324 galaxies within the Calar Alto Legacy Integral Field Area (CALIFA) survey are used for this purpose. We perform a detailed light-profile classification, finding that 84% of our disks show down- or up-bending profiles (Type II and Type III, respectively), while the remaining 16% are well fitted by one single exponential (Type I). The analysis of the color gradients at both sides of this break shows a U-shaped profile for most Type II galaxies with an average minimum (g′ − r′) color of ~0.5 mag and an ionized-gas metallicity flattening associated with it only in the case of low-mass galaxies. Comparatively, more massive systems show a rather uniform negative metallicity gradient. The correlation between metallicity flattening and stellar mass for these systems results in p-values as low as 0.01. Independent of the mechanism having shaped the outer light profiles of these galaxies, stellar migration or a previous episode of star formation in a shrinking star-forming disk, it is clear that the imprint in their ionized-gas metallicity was different for low- and high-mass Type II galaxies. In the case of Type III disks, a positive correlation between the change in color and abundance gradient is found (the null hypothesis is ruled out with a p-value of 0.02), with the outer disks of Type III galaxies with masses ≤10^10 M_⊙ showing a weak color reddening or even a bluing. This is interpreted as primarily due to a mass downsizing effect on the population of Type III galaxies that recently experienced an enhanced inside-out growth., Unión Europea. FP7, Ministerio de Economía y Competitividad (MINECO), España, Campus de Excelencia Internacional Moncloa (CEI), Acciones Marie Curie (UE), Ministerio de Educación, Cultura y Deporte (MECD), España, Ministry of Economy, Development, and Tourism's Millennium Science Initiative, Fondo Nacional de Desarrollo Científico, Tecnológico y de Innovación Tecnológica (FONDECYT), Chile, Iniciativa Científica Milenio (ICM), Chile, FCT Investigator Programme, Portugal, Ministerio de Educación y Ciencia (MEC), Portugal, Dirección General Asuntos del Personal Académico-UNAM, México, Fondos FEDER (UE), Plan Estatal de Investigación Científica y Técnica y de Innovación 2013-2016 I+D+i (MINECO), España, Ministerio Economía, Fomento y Turismo (MEFT), Chile, Millennium Institute of Astrophysics (MAS), Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), Chile, Universidad Nacional Autónoma de México (UNAM), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© ESO 2014. We wish to thank Brad Gibson and Pierre Ocvirk for their constant advice. P.S.-B. acknowledges support from the Ramón y Cajal program, grant ATA2010-21322-C03-02 from the Spanish Ministry of Economy and Competitiveness (MINECO). F.F.R.O. acknowledges the Mexican National Council for Science and Technology (CONACYT) for financial support under the programme Estancias Posdoctorales y Sabáticas al Extranjero para la Consolidación de Grupos de Investigación, 2010-2012. We acknowledge financial support from the research projects under grants AYA2010-21887-C04-03, AYA2010-21322-C03-03 and AYA2010-15081 by the Spanish Ministerio de Ciencia e Innovación. J.F.-B. acknowledges support from the Ramón y Cajal Program, grants AYA2010-21322-C03-02 from the Spanish Ministry of Economy and Competitiveness (MINECO). R. A. M. is funded by the Spanish program of International Campues of Excellence Moncloa (CEI). C.J.W. acknowledges support through the Marie Curie Career Integration Grant 303912. I.M. acknowledges financial support from the Junta de Andalucía through projects PO8-TIC-03531 and TIC114, and the Spanish Ministry of Economy and Competitiveness (MINECO) through the project AYA2010-15169. We acknowledge the usage of the HyperLeda database (http://leda.univ-lyon1.fr). Based on observations collected at the Centro Astronómico Hispano-Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut ur Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). FCT/MCTES (Portugal) and POPH/FSE (EC). He acknowledges support by the Fundacao para a Ciencia e a Tecnologia (FCT) under project FCOMP-01-0124-FEDER-029170 (Reference FCT PTDC/FIS-AST/3214/2012), funded by FCT-MEC (PIDDAC) and FEDER (COMPETE). We also thanks the referee por his/her suggestions that have improved the final version of this paper., While studies of gasphase metallicity gradients in disc galaxies are common, very little has been done towards the acquisition of stellar abundance gradients in the same regions. We present here a comparative study of the stellar metallicity and age distributions in a sample of 62 nearly face-on, spiral galaxies with and without bars, using data from the CALIFA survey. We measure the slopes of the gradients and study their relation with other properties of the galaxies. We find that the mean stellar age and metallicity gradients in the disc are shallow and negative. Furthermore, when normalized to the effective radius of the disc, the slope of the stellar population gradients does not correlate with the mass or with the morphological type of the galaxies. In contrast to this, the values of both age and metallicity at similar to 2.5 scale lengths correlate with the central velocity dispersion in a similar manner to the central values of the bulges, although bulges show, on average, older ages and higher metallicities than the discs. One of the goals of the present paper is to test the theoretical prediction that non-linear coupling between the bar and the spiral arms is an efficient mechanism for producing radial migrations across significant distances within discs. The process of radial migration should flatten the stellar metallicity gradient with time and, therefore, we would expect flatter stellar metallicity gradients in barred galaxies. However, we do not find any difference in the metallicity or age gradients between galaxies with and without bars. We discuss possible scenarios that can lead to this lack of difference., Ramón y Cajal program from the Spanish Ministry of Economy and Competitiveness (MINECO), Mexican National Council for Science and Technology (CONACYT), Spanish Ministerio de Ciencia e Innovación, Spanish program of International Campus of Excellence Moncloa (CEI), Marie Curie Career Integration Grant, Junta de Andalucía, Spanish Ministry of Economy and Competitiveness (MINECO), Fundacao para a Ciencia e a Tecnologia (FCT), FCT-MEC (PIDDAC), FEDER (COMPETE), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

Through stars, the formation and evolution of the Galaxy goes hand-in-hand with the cosmic origin of the elements. As stars form, they carry chemical fingerprints of their birthclouds, providing us with chemical timestamps of the Galaxy.The detailed history of the Galactic disk and bulge is still to be untagled. The same goes for the origin of elements – where some still have elusive origins. Disentagling the origin of the Galaxy and the elements can only be acchived by continued efforts by combining the most accurate and precise data with the latest state-of-the art theoretical models.In this thesis, I present high-precision chemical abundances of red giant stars in the Galactic disk and bulge, obtained by careful analysis of high-resolution optical and infrared spectra. Using red giant stars in the bulge and disk populations allows for an unique differential comparison of the two Galactic components. I focus the analysis to obtain abundances of neutron-capture elements, which can shed new light on the origin of the Galactic components.The abundance trends of the Galactic bulge show great similarities with the Galactic (thick) disk, pointing at a similar history. However, there are possible enrichments in both lanthanum and molybdenum, which require further follow-up studies to confirm. I identify a chemically-peculiar star in the bulge, standing out by its high abundances of europium and molybenum.Finally, I demonstrate the need for high-resolution and spectra in order to access abundances of neutron-capture elements in the infrared. Including heavy elements is essential in getting the full chemical view of the Galaxy, which is shown in this thesis.

Aims. In this work, we aim to make a differential comparison of the neutron-capture and p-process element molybdenum (Mo) in the stellar populations in the local disk(s) and the bulge, focusing on minimising possible systematic effects in the analysis.Methods. The stellar sample consists of 45 bulge and 291 local disk K-giants observed with high-resolution optical spectra. The abundances are determined by fitting synthetic spectra using the Spectroscopy Made Easy (SME) code. The disk sample is separated into thin and thick disk components using a combination of abundances and kinematics. The cosmic origin of Mo is investigated and discussed by comparing with published abundances of Mo and the neutron-capture elements cerium (Ce) and europium (Eu).Results. We determine reliable Mo abundances for 35 bulge and 282 disk giants with a typical uncertainty of [Mo/Fe] similar to 0.2 and similar to 0.1 dex for the bulge and disk, respectively.Conclusions. We find that the bulge is possibly enhanced in [Mo/Fe] compared to the thick disk, which we do not observe in either [Ce/Fe] or [Eu/Fe]. This might suggest a higher past star-formation rate in the bulge; however, as we do not observe the bulge to be enhanced in [Eu/Fe], the origin of the molybdenum enhancement is yet to be constrained. Although the scatter is large, we may be observing evidence of the p-process contributing to the heavy element production in the chemical evolution of the bulge.

Large fractions of metals are missing from the observable gas-phase in the interstellar medium (ISM) because they are incorporated into dust grains. This phenomenon is called dust depletion. It is important to study the depletion of metals into dust grains in the ISM to investigate the origin and evolution of metals and cosmic dust. We characterize the dust depletion of several metals from the Milky Way to distant galaxies. We collected measurements of ISM metal column densities from absorption-line spectroscopy in the literature, and in addition, we determined Ti and Ni column densities from a sample of 70 damped Lyman-alpha absorbers (DLAs) toward quasars that were observed at high spectral resolution with the Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES). We used relative ISM abundances to estimate the dust depletion of 18 metals (C, P, O, Cl, Kr, S, Ge, Mg, Si, Cu, Co, Mn, Cr, Ni, Al, Ti, Zn, and Fe) for different environments (the Milky Way, the Magellanic Clouds, and DLAs toward quasars and towards gamma-ray bursts). We observed overall linear relations between the depletion of each metal and the overall strength of the dust depletion, which we traced with the observed [Zn/Fe]. The slope of these dust depletion sequences correlates with the condensation temperature of the various elements, that is, the more refractory elements show steeper depletion sequences. In the neutral ISM of the Magellanic Clouds, small deviations from linearity are observed as an overabundance of the alpha-elements Ti, Mg, S, and an underabundance of Mn, including for metal-rich systems. The Ti, Mg, and Mn deviations completely disappear when we assume that all systems in our sample of OB stars observed toward the Magellanic Clouds have an alpha-element enhancement and Mn underabundance, regardless of their metallicity. This may imply that the Magellanic Clouds have recently been enriched in alpha-elements, potentially through recent bursts of star fo