The physics pertaining to the asymptotic giant branch (AGB) phase of stellar evolution has been studied for many years. However, the mechanics behind many characteristics displayed at this stage are still not fully understood. As a member of the Long Period Variable class of stars, AGB stars are invaluable in creating three-dimensional maps of the Milky Way, the Magellanic System and other galaxies with resolved stellar populations. Variable stars can be used to determine radial distances from Earth using their periodic luminosity variations. As this type of star has unknown qualities, models of AGB populations need to be calibrated with observed data. Previous research has derived a best-fitting model using the TRILEGAL code (a TRIdimensional modeL of thE GALaxy). This model was calibrated against single-epoch luminosity functions (LFs) calculated from resolved stellar populations in the Small Magellanic Cloud (SMC). With multi-epoch data now available from the VISTA survey of the Magellanic Clouds (VMC), this best-fitting model can now be compared with the LFs as they vary with time. Firstly, statistical tests are completed to measure the extent of the LF variation between epochs and from the mean LF for both the full VMC AGB catalogue and for the oxygen-rich, carbon-rich and extreme AGB classes. Statistical tests are then performed to measure the similarity between the LFs from different epochs and the simulated LFs, again for the entire sample and the three classes. This investigation shows that, while the current best-fitting model is a good approximation of many individual epochs’ AGB LFs in the SMC to within 3σ, inclusion of multi-epoch data would make for a more robust analysis. In order to do this, it would be desirable to have more epochs with deeper and regular observations that could cover full lightcurves of some of the sources. There also seems to be a statistical difference between the inner and outer areas of the SMC, perhaps due to tidal disruptions. It would be interesting to see the results of a similar study using the LMC, which is less affected by the gravitational influence of its smaller companion. / <p>This thesis was written under the supervision of Maria-Rosa Cioni at the Leibniz Institute for Astrophysics in Potsdam. The presentation was held online due to the COVID-19 pandemic.</p>

We conduct a broad investigation about stellar mass and population diagnostics in order to formulate novel constraints related to the formation and evolution of galaxies from a nearby cluster environment. Our work is powered by the use of stellar population models which transform galaxy colours and/or absorption line strengths into estimates of its stellar properties. As input to such models, we assemble an extensive compilation of age and chemical abundance information for Galactic globular clusters. This compilation allows a confident expansion of these models into new regions of parameter space that promise to refine our knowledge of galactic chemical evolution. We then draw upon a state-of-the-art spectroscopic and photometric survey of the Virgo galaxy cluster in order to constrain spatial variations of the stellar ages, metallicities, and masses within its member galaxies, and their dynamical masses. We interpret these data in the context of the histories of star formation, chemical enrichment, and stellar mass assembly to formulate a broad picture of the build-up of this cluster’s content over time. In it, the giant early-type galaxies formed through highly dissipational processes at early times that built up most of their stellar mass and drew significant amounts of dark matter within their optical radii. Conversely, dwarf early-types experienced environmental processes that quenched their star formation during either the early stages of cluster assembly or upon infall at later times. Somewhat perplexing is our finding that the internal dynamics of these galaxies are largely explained by their stellar masses. Lastly, Virgo spirals also suffer from their dense environment, through ram pressure stripping and/or tidal harrassment. In addition to quenching, these effects leave an imprint on their internal dynamical evolution too. Late-type spirals exhibit evidence of having ejected significant amounts of baryons from their inner regions, likely via energetic feedback events. Rich as our picture of the history of the Virgo cluster has become, real progress in our understanding of this system will truly benefit from future high-resolution cosmological and hydrodynamic simulations of this environment. Such simulations are still in their infancy, but the data assembled here should soon provide their most direct validation. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-09-30 23:32:48.575

In this thesis I present an investigation into the presence, nature and origin of the thick disk component in late-type galaxies. I use ground-based wide-field observations to study two edge-on low-mass galaxies in the Local Universe: NGC 4244 and NGC 55. The large field-of-view of the ground-based data enables me to inspect the radial and vertical structure of each galaxy. The vertical profiles are studied up to larger distances fromthemid-plane than in any previous study and the presence of a second disk component beyond the thin disk with a larger scale height is revealed for both galaxies. The high-quality data allows me to carry out stellar population and metallicity studies for stars above and below the plane. Furthermore, direct comparisons with two simulated low-mass galaxies provided by the Preston group at the University of Central Lancashire are carried out. By putting the results for NGC 4244 and NGC 55 into context with the thick disk properties from these simulations and from the literature, the most likely thick disk formation scenarios can be pointed out. The bulgeless low-mass systemNGC 4244 lies at a distance of 4.4 Mpc and is studied using V- and I-band wide-field images taken with Suprime-Cam on the Subaru telescope, Hawaii. The extra-planar regions of NGC 4244 show the presence of a large population of Red Giant Branch (RGB) stars and some Asymptotic Giant Branch (AGB) stars. The best strategy to study the presence and structure of a thick disk component is to use the vertical diffuse light profiles in the crowded central regions and RGB star counts in the sparser and sky background dominated outskirts. The profiles show evidence for the presence of a sparsely populated second structural component beyond ∼ 2 kpc above and below the mid-plane. The profiles are fitted with a twodisk model, where each disk is approximated by an isothermal, self-gravitating sheet. A Bayesian model comparison confirms the need for a second disk component in the profile fit. Furthermore, the AGB profiles are inspected and are found to have a lower scale height than the RGB profiles. Metallicity studies of the RGB population in the thick disk component reveal that the metallicity is much lower than the solar metal-licity. Last, the scale length of the thin disk is quantified from the diffuse light radial profiles. At a distance of 1.9 Mpc the Magellanic type low-mass galaxy NGC 55 is studied using V- and I-band images from the VIsible MultiObject Spectrograph (VIMOS) in imaging mode on the Very Large Telescope (VLT, UT3) on Cerro Paranal, Chile. The very central regions of the galaxy are not covered by the VIMOS pointings so I use additional images from the Curtis-Schmidt telescope on Cerro Tololo. As for NGC 4244, I find that the RGB star count profiles extend to larger scale heights than the AGB profiles. The combined diffuse light + RGB profiles show evidence for a very prominent second disk component beyond ∼ 2 kpc above and below the plane. The metallicity studies of the RGB population show, that there is no trend in themetallicity with height above or below the plane. As for NGC 4244 the metallicity is significantly lower than the solar metallicity. Furthermore, the scale length of the thin and thick disk is derived from the radial profiles. The properties of thick disks in galaxies of all masses is studied by compiling the results fromobserved and simulated galaxies in the literature in addition to the results for NGC 4244, NGC 55 and the two simulated low-mass galaxies provided by the Preston group. By studying the similarities, differences and global trends with mass in the thick disk properties it is possible to confront the thick disk formation models. I find that none of the formation scenarios can be ruled out and even a hybrid scenario is possible.

Cette thèse a pour objectif de contribuer à comprendre l'histoire de formation de notre Galaxie, la Voie lactée, en utilisant pour traceurs des objets parmi les plus vieux de l'univers que sont les amas globulaires, amas d'étoiles denses liées gravitationnellement, et les étoiles de champ.Selon le modèle de croissance hiérarchique des structures, les galaxies se construisent, en partie, par la fusion de galaxies moins massives. La Voie lactée ne fait pas exception et l’histoire de ses accrétions peut se lire également dans sa population d’amas globulaires qui contient à la fois des amas globulaires formés en son sein et d'autres d'origine extragalactique. Si les amas globulaires les plus distants du centre Galactique sont souvent associés au halo externe, dans les régions plus internes, où se situe la plupart de la masse stellaire de notre Galaxie, l'association d'amas globulaires avec les populations stellaires est encore très largement débattue.Dans ce travail, nous utilisons le lien étroit entre les amas globulaires et les étoiles de champ ainsi que des simulations numériques pour tenter de lever l'ambiguïté sur l'origine in situ ou accrétée de ces objets et reconstruire l'histoire d'accrétion de la Voie Lactée. Dans un premier temps, nous étudions la distribution spatiale, la cinématique et l'abondance chimique des amas globulaires à forte métallicité. Nous montrons que leurs propriétés spatiales, dynamiques et chimiques sont en bon accord avec celles de la population stellaire du disque épais de la Galaxie. Nous suggérons alors une époque commune de formation et d'évolution entre les amas globulaires riches en métaux et le disque épais vieux de la Galaxie. Dans un second temps, nous analysons l'efficacité des diagnostiques cinématiques qui ont été proposés pour identifier les débris d'accrétion parmi les étoiles de champ et nous discutons leurs applications aux amas globulaires galactiques. Pour ce faire, nous utilisons des simulations numériques auto-consistantes qui modélisent l'accrétion d'une ou plusieurs galaxies satellites dans un potentiel galactique. Nous montrons, d'une part, que les intégrales du mouvement ne sont pas conservées durant le processus d'accrétion et qu'ainsi, à l'issue de la fusion, les étoiles et les amas globulaires accrétés ne retiennent pas l'information initiale sur les propriétés orbitales de leurs satellites progéniteurs. D'autre part, l’interaction avec des galaxies satellites chauffe les populations in situ (étoiles et amas globulaires) qui, en réaction, peuplent spatialement le halo galactique et les régions préférentiellement occupées par des objets d'origine extragalactique dans les espaces cinématiques.En conséquence, ce travail montre que, dans le contexte de l'arrivée des données Gaia, l’identification des débris d’accrétion au sein de la Voie lactée à l’aide des seuls diagnostiques cinématiques sera difficile, et nécessitera l’utilisation de mesure d’abondances chimiques détaillées. / The goal of this thesis is to contribute to understand the formation history of our Galaxy, the Milky Way, using as tracers some among the oldest objects in the universe, the globular clusters, and field stars.In the LambdaCDM paradigm, one of the main mechanisms of galaxy growth is by means of satellite accretion. The Milky Way is no exception and the history of its accretions can be read also in its population of globular clusters, containing both in-situ and accreted members. While for clusters at large distances from the Galactic centre an extragalactic origin is often proposed, in the inner regions, where most of the stellar mass of our Galaxy lies, the link between globular clusters and stellar populations is still very widely debated.In this work, we use the close link between globular clusters and field stars, as well as numerical simulations, to try to remove the ambiguity on the in-situ or accreted origin of these objects and to reconstruct the accretion history of the Milky Way. As a first step, we study the spatial distribution, kinematics and chemical abundances of metal-rich ([Fe/H] > -1) globular clusters. We show that their spatial, kinematic and chemical properties are in good agreement with those of the stellar population of the thick disk of the Galaxy. We then suggest that metal-rich globular clusters and Galactic thick disk share the same epoch of formation and evolution. Secondly, we analyze the overall efficiency of kinematic diagnostics that have been proposed to identify merger debris among the field stars and discuss their application to the galactic globular cluster system. To do this, we use self-consistent numerical simulations that model the accretion of one or more satellite galaxies in a Milky Way-like potential. On the one hand, we show that the integrals of motion are not conserved during the accretion process. As a result, after the merger, accreted stars and globular clusters do not retain the initial information about the orbital properties of their progenitor satellites. On the other hand, mergers of small galaxies and tidal interactions may cause the heating of the in-situ populations (stars and globular clusters) which, in response, populate the galactic halo and the regions in the kinematic spaces preferentially occupied by objects with an extragalactic origin.In the context of the arrival of Gaia data, this work shows that the identification of debris of past accretion events experienced by the Milky Way using only kinematic diagnostics will be extremely challenging. Detailed chemical abundances and/or ages will be fundamental to disentangle the accreted or in-situ nature of the Galactic stellar populations.

Nós realizamos um estudo estatístico do comportamento de perfis de cor em bandas largas (UBV) para 257 galáxias espirais do tipo Sbc, ordinárias e barradas, utilizando dados obtidos através de fotometria fotoelétrica de abertura, disponíveis na literatura (Longo & de Vaucouleurs 1983,1985). Nós determinamos os gradientes de cor (B-V) e (U-B) para as galáxias da amostra total, bem como os índices de cor (B-V) e (U-B) de bojos e discos separadamente, utilizando métodos estatísticos robustos. Utilizamos uma técnica de decomposição bi-dimensional para modelar os perfis de brilho de bojos e discos em imagens dos arquivos do ``Digitised Sky Survey' (DSS), obtendo parâmetros estruturais característicos para 39 galáxias. A aquisição de imagens de 14 galáxias no Laboratório Nacional de Astrofísica permitiu-nos realizar um estudo fotométrico comparativo, e atestar a validade dos resultados obtidos neste estudo. Entre os principais resultados obtidos, destacam-se: (i) - 65% das galáxias possuem gradientes de cor negativos (mais vermelhos no centro), 25% possuem gradientes nulos, e 10% apresentam gradientes positivos; (ii) - galáxias que apresentam gradientes de cor nulos tendem a ser barradas; (iii) - os índices de cor ao longo das galáxias com gradientes nulos são similares aos índices de cor dos discos das galáxias com gradientes negativos; (iv) - confirmamos a correlação entre os índices de cor de bojos e discos, já obtida por outros autores; (v) - a ausência de correlação entre os gradientes de cor e de metalicidade sugere que o excesso de galáxias barradas com gradientes de cor nulos ou positivos reflete uma diferença no comportamento da idade média da população estelar ao longo de galáxias barradas e ordinárias; (vi) - galáxias com gradientes de cor nulos ou positivos têm uma leve tendência a apresentar bojos maiores e com maior concentração central de luz; e (vii) - confirmamos a correlação entre as escalas de comprimento de bojos e discos, já obtida por outros autores. Estes resultados são compatíveis e favoráveis ao cenário de evolução secular, no qual barras produzem fluxos radiais de massa para as regiões centrais de galáxias, não somente homogeneizando as populações estelares ao longo de galáxias, produzindo discos e bojos com índices de cor semelhantes, mas também contribuindo para a formação e/ou construção de bojos. / We have done a statistical study of the behaviour of the broadband color profiles (UBV) for 257 Sbc galaxies, barred and unbarred, collecting data obtained through photoeletric aperture photometry, available in the literature (Longo & de Vaucouleurs 1983,1985). We have determined (B-V) and (U-B) color gradients for the total sample of galaxies, as well as (B-V) and (U-B) color indices of bulges and disks separately, using robust statistical methods. Applying a bi-dimensional decomposition technique to model the brightness profiles of bulges and disks in images from the Digitised Sky Survey (DSS), we obtained characteristic structural parameters for 39 galaxies. The acquisition of images for 14 galaxies in the Laboratório Nacional de Astrofísica (Astrophysics National Laboratory) allowed us to do a comparative photometric study, and verify the validity of the results obtained in this work. Among the main results obtained, we point out: (i) - 65% of the galaxies have negative color gradients (reddish inward), 25% have zero gradients, and 10% show positive gradients; (ii) - galaxies that show zero color gradients tend to be barred; (iii) - the color indices along the galaxies with zero color gradients are similar to the color indices of the disks of the galaxies with negative color gradients; (iv) - we confirm the correlation between the color indices of bulges and disks, already found by other authors; (v) - the absence of correlation between color and metallicity gradients suggests that the excess of barred galaxies with zero or positive color gradients reflects a difference in the behaviour of the mean age of the stellar population along barred and unbarred galaxies; (vi) - galaxies with zero or positive color gradients show a slight tendency of having larger bulges, with a greater central concentration of light; and (vii) - we confirm the correlation between the scale lenghts of bulges and disks, already found by other authors. These results are compatible and favourable to the secular evolutionary scenario, in which stellar bars induce radial mass fluxes to the central regions of galaxies, not only turning homogeneous the stellar populations along the galaxies, producing disks and bulges with similar color indices, but also contributing to the formation and/or building of galactic bulges.

Blue compact galaxies (BCGs) are gas-rich star-forming low redshift galaxies with low metallicities. In some cases the relative strength of the starburst can be so high that it completely dominates the light output of the galaxy, an obstacle which has been countered by deeper optical imaging data and observations in the near infra-red (NIR) regime. This has revealed an older population referred to as the "host". In an effort to study the hosts of BCGs we have analyzed new and extremely deep UBVRIHKs imaging data for 46 high and low luminosity BCGs. For several BCGs the data reveal previously undetected extended low surface brightness components beyond the μB~26 mag arcsec-2 isophote. These are predominantly the luminous BCGs in the sample, and they show tails, plumes, optical bridges between companion galaxies, and other signs of merging or strong tidal interactions. The low luminosity BCGs, on the other hand, are well represented by an exponential disk profile down to the reliability limit of the data at a surface brightness level of μB~28 mag arcsec-2. The burst and host populations are examined separately. The integrated colors of both are compared to predictions from spectral evolutionary models, giving an indication of their respective ages and metallicities. Our analysis suggests that for the luminous BCGs a strong contribution by nebular emission is present almost down to the Holmberg radius, invalidating the host structural parameters obtained from brighter isophotes. Possible evolutionary links to quiescent galaxies like dEs, dIs, and LSBGs are explored by examining the structural parameters derived from two radial ranges typically assumed to be dominated by the underlying host galaxy. In this parameter space the luminous BCGs in our sample deviate from their low luminosity counterparts and from BCG data in the literature. They are instead consistent with the structural properties of giant low surface brightness galaxies with central surface brightnesses μB≥23 mag arcsec-2. We further examine the asymmetry and concentration parameters for the sample and study the correlation between the minimum asymmetry distribution in the optical and NIR vs morphological class, concentration and integrated colors to identify mergers/tidally interacting galaxies. A shift in the asymmetry distribution occurs for low luminosity BCGs from the optical to the NIR. In contrast, we find that the flocculent asymmetry component (due to star formation) completely dominates the composite asymmetry of high luminosity BCGs. We introduce an alternative asymmetry measure which successfully traces the dynamical asymmetry component (due to merging/tidal interaction) of the host. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.</p>

This thesis presents observations and analysis relating to the understanding of processes that govern the formation and evolution of low mass galactic systems. In particular we have focused on separating out the contribution to the chemical and dynamical evolution of dwarf galaxies due to solely secular (internal) processes compared to external effects from the local environment a galaxy resides in. Our observational data focus on an extremely isolated dwarf galaxy, WLM, which we demonstrate has had a uniquely quiescent tidal history, thereby making it an excellent test case for such a study. With spectroscopic and photometric observations of the resolved stars and neutral gas in WLM we have been able to characterize the chemical, structural and kinematic properties of this gas rich dwarf galaxy. As WLM has not been subject to strong tidal or ram-pressure stripping of its stellar and gaseous populations, we have been able to compare the dynamical evolution and chemical history of WLM to theoretical models which are environment independent. A differential comparison of WLM to more environmentally processed dwarf galaxies in the Local Group has revealed that WLM's structural and dynamical state is far from the idealized picture of dIrrs as thin gas-rich rotating systems. The stellar component of WLM shows equal parts rotation and dispersion, and both the gaseous and stellar structural properties show an intrinsically thick axisymmetric configuration. The time evolution of the random (dispersion) component of the stellar orbital energy shows an increase with stellar age, which we show is consistent with secular processes alone - such as disk heating from giant molecular clouds and dark matter substructure. While the degree to which the thick structural and dynamically hot configuration for WLM is surprising, its chemical properties show remarkably consistent values with other galaxies of the same halo mass. Comparing the spatial chemical trends in WLM with other dwarf galaxies we identify a correlation between the strength of the radial abundance gradients and the angular momentum content of dwarf galaxies in the Local Group. Finally using a large sample of chemical abundance measurements in the literature for dwarf galaxies and star clusters, we demonstrate that their distributions of chemical elements all exhibit a binomial form, and use the statistical properties of the distributions to identify a new metric for differentiating low luminosity stellar systems. We further apply a simple binomial chemical evolution model to describe the self-enrichment and pre-enrichment in the two classes of objects, and suggest how this may be used to place constraints on the formation environments of globular clusters in particular. / Graduate

abstract: Most stars form in groups, and these clusters are themselves nestled within larger associations and stellar complexes. It is not yet clear, however, whether stars cluster on preferred size scales within galaxies, or if stellar groupings have a continuous size distribution. I have developed two methods to select stellar groupings across a wide range of size-scales in order to assess trends in the size distribution and other basic properties of stellar groupings. The first method uses visual inspection of color-magnitude and color-color diagrams of clustered stars to assess whether the compact sources within the potential association are coeval, and thus likely to be born from the same parentmolecular cloud. This method was developed using the stellar associations in the M51/NGC 5195 interacting galaxy system. This process is highly effective at selecting single-aged stellar associations, but in order to assess properties of stellar clustering in a larger sample of nearby galaxies, an automated method for selecting stellar groupings is needed. I have developed an automated stellar grouping selection method that is sensitive to stellar clustering on all size scales. Using the Source Extractor software package on Gaussian-blurred images of NGC 4214, and the annular surface brightness to determine the characteristic size of each cluster/association, I eliminate much of the size and density biases intrinsic to other methods. This automated method was tested in the nearby dwarf irregular galaxy NGC 4214, and can detect stellar groupings with sizes ranging from compact clusters to stellar complexes. In future work, the automatic selection method developed in this dissertation will be used to identify stellar groupings in a set of nearby galaxies to determine if the size scales for stellar clustering are uniform in the nearby universe or if it is dependent on local galactic environment. Once the stellar clusters and associations have been identified and age-dated, this information can be used to deduce disruption times from the age distribution as a function of the position of the stellar grouping within the galaxy, the size of the cluster or association, and the morphological type of the galaxy. The implications of these results for galaxy formation and evolution are discussed. / Dissertation/Thesis / Ph.D. Astrophysics 2011

Population synthesis models (PSMs) are fundamental tools to study the star formation history and IMF of unresolved stellar populations using spectral features. This work presents a new set of PSMs constructed using theoretical isochrones and two state-ofthe- art synthetic spectral libraries. The BT-Settl and Munari libraries were chosen for their ability to predict the observed values of Lick-type and IMF-sensitive indices in individual stars of the solar neighbourhood. The BT-Settl library was used to sample the cool main sequence stars and the Munari library for the rest of the evolutionary phases. The PSMs cover a range of metallicities with [Fe/H]= 0, -1.31 and -1.81 for scaled-solar and α-enhanced metal mixtures. The models were used to study the behaviour of the IMF indices defined in the literature and the results are in good agreement with what other PSMs have determined. The PSMs in this work predict a strong degeneracy between age, metallicity and IMF. I used the models to study which are the main evolutionary phases contributing to each IMF-sensitive index and found that most indices reach their final integrated values before the turn off. The post-main sequence stars contribute mainly to the continuum of these bands. Uncertainties in the the effective temperature of the isochrones can affect IMF estimates. The PSMs were applied to extragalactic globular clusters (GCs) and early-type galaxies (ETGs) using data from the literature. I determined the ages, metallicities and IMFs of these systems using index combinations in the optical and infrared. I explored how the morphology of the Horizontal Branch (HB) and dynamical evolution (which are key uncertainties in the modelling of GCs) can affect the IMF predictions. In a population with a Milky Way IMF, dynamical evolution can make the IMF indices mimic a bottom-light IMF. HB morphology has no impact on the IMF estimates at low [Fe/H]. In the IMF index-index diagrams for GCs, the results are significantly affected by the unknown sodium abundances of these systems. Using the PSMs in this work the best index combination to determine the IMF is CaH1 and TiO2. The ETGs and the [Fe/H]=0 GCs appear to have a bottom-heavy IMF with x ~ 3:0. These results are discussed in the work.

The Galactic disk is home of many billion stars, one of which isour Sun. The stellar population of which the Sun is a member residesin the vertically thin spiral structure of the disk. There is a seconddisk population, the so-called thick disk, that has somewhat dierentspatial, kinematic and chemical properties as compared to the thindisk. It may be systematically older than the thin disk (Bernkopf et al.2001), with a star-formation hiatus separating the two. Observationsof thick-disk subgiants allow us to probe the chemical properties ofthese stars. As the subgiant evolutionary phase is short, age-datingthese stars is also possible. Are they in fact systematically older thanthe oldest thin-disk stars? This project will take rst steps towardsanswering this question based on new target selections done on DataRelease 1 of the Gaia mission. / Vintergatans disk innehåller flera miljarder stjärnor, varav en är vår Sol. Den stjärnbefolkning som Solen är medlem i ligger i den vertikalt tunna spiralstrukturen på skivan (tunna disken). Det finns en andra diskpopulation, den så kallade tjocka disken, som har något annorlunda rumsliga, kinematiska och kemiska egenskaper jämfört med den tunna disken. Den kan vara äldren än tunna disken (Bernkopf et al. 2001), med en stjärnbildningsstopp som skiljer de två. Genom att observera subjättar som är en del av den tjocka disken blir det möjligt att analysera dessa stjärnors kemiska egenskaper. Eftersom subjätte grenen är en kort evolutionär fas, åldersbestämmelse är också möjlig för dessa stjärnor. Är de faktiskt systematiskt äldre än de äldsta tunna diskens stjärnor? Detta projekt kommer att ta de första stegen mot att svara på denna fråga baserat på nya målval som gjorts på Data Release 1 från Gaia-uppdraget.