Populações extremas da Via Láctea : do regime substelar aos componentes externos

We present here the study of the properties of two different populations of our Galaxy: the very low-mass stellar and substellar regime of ultracool dwarfs and the halo stellar population. For the ultracool dwarfs, we follow the same approach as in our previous investigations presented in Carnero Rosell et al. (2019), dal Ponte et al. (2020) using the first data release of the Dark Energy Survey. Our past work resulted in two important catalogs: 11,745 ultracool dwarf candidates and 264 wide binary and multiple system candidates involving at least one ultracool dwarf. Here we present the revision and an update of the method to search for and characterize ultracool dwarfs. We obtain a sample of 19,583 ultracool dwarf candidates brighter than z ≤ 23 selected from the Dark Energy Survey second data release matched to VHS DR6, VIKING DR5 and AllWISE covering ∼ 4,800 deg2 in the Southern Hemisphere. The ultracool candidates were first pre-selected based on their (i-z), (z-Y), and (Y-J) colors. They were further classified using a method that compares their optical, near-infrared and mid-infrared colours against templates of M, L and T dwarfs. 14,099 objects are presented as new L and T candidates and the remaining objects are from the literature, including 5,342 candidates from our previous work. We also show spectra of twelve new ultracool dwarfs discovered by our group. These spectroscopically confirmed objects are a sanity check of our selection of ultracool dwarfs and photometric classification method. Using this new and deeper sample of ultracool dwarf candidates we found: 20 new candidate members to nearby young moving groups and associations, variable candidate sources and four new wide binary systems composed of two ultracool dwarfs. We also show a method to estimate the thin disk scale height for the L dwarf population and discuss its current limitations. For the investigation of the Milky Way halo, we use a catalog with StarHorse stellar parameters, distances and extinctions catalog derived from Gaia EDR3 combined with photometric catalogs for stars brighter than G = 18.5. This catalog is used to select halo stars based on their tangential velocity. We also apply a geometric and an extinction cut to eliminate disk contaminants. We calculate pseudo cartesian velocities and check the consistency of our selection. We then present an initial study of the metallicity distribution for the local halo. With our sample of more than 2 million halo stars, we confirm previous measurements of metallicity presented in the literature, including an estimate for the Gaia-Enceladus component. We also show a clear metallicity gradient present in our sample.Apresentamos aqui o estudo das propriedades de duas populações diferentes da nossa Galáxia: o regime de estrelas de baixa massa e o regime sub-estelar de anãs ultrafrias e a população estelar do halo. Para as anãs ultrafrias, seguimos a mesma abordagem de nossos trabalhos anteriores em Carnero Rosell et al. (2019), dal Ponte et al. (2020) usando o primeiro data release do Dark Energy Survey. Nosso trabalho resultou em dois catálogos importantes: 11.745 candidatas a anãs ultrafrias e 264 candidatas a sistemas binários e múltiplos envolvendo pelo menos uma anã ultrafria. Aqui apresentamos a revisão e atualização do método de busca e caracterização de anãs ultrafrias. Obtivemos uma amostra de 19.583 candidatas mais brilhantes que z ≤ 23 selecionadas a partir do segundo data release do Dark Energy Survey combinado com VHS DR6, VIKING DR5 e AllWISE cobrindo ∼ 4.800 deg2 no Hemisfério Sul. As candidatas a anãs ultrafrias foram primeiro pré-selecionadas com base em suas cores (i-z), (z-Y) e (Y-J). Também, foram posteriormente classificadas usando um método que compara suas cores no óptico, infravermelho próximo e infravermelho médio com modelos de anãs M, L e T. 14.099 objetos são apresentados aqui como novos candidatos a anãs L e T e os objetos restantes são da literatura, incluindo 5.342 candidatas do nosso trabalho anterior. Além disso, mostramos espectros de doze novas anãs ultrafrias descobertas por nosso grupo. Esses objetos espectroscopicamente confirmados servem como uma verificação de nossa seleção e do método de classificação fotométrico. Usando a nova amostra de candidatas, encontramos: 20 novos candidatos a membros de grupos e associações jovens próximas, candidatos a fontes variáveis e quatro novos sistemas binários de alta separação compostos por duas anãs ultrafrias. Também mostramos um método para estimar a escala de altura do disco fino para a população de anãs L e discutimos as suas limitações. Para a investigação do halo da Via Láctea, utilizamos um catálogo de parâmetros estelares, distâncias e extinções do StarHorse derivado do Gaia EDR3 combinado com outros catálogos fotométricos para estrelas com brilho superior a G = 18,5. Este catálogo é usado para selecionar estrelas do halo com base em sua velocidade tangencial. Aplicamos um corte geométrico e de extinção para eliminar os contaminantes do disco. Calculamos pseudo velocidades cartesianas para checar a consistência da nossa seleção. Apresentamos um estudo inicial da distribuição de metalicidade para o halo local. Com a nossa amostra de mais de 2 milhões de estrelas, confirmamos medições anteriores de metalicidade apresentadas na literatura, incluindo uma estimativa para a componente do Gaia-Enceladus. Também mostramos um claro gradiente em metalicidade presente na nossa amostra

Procura, classificação espectral e benchmarking de anãs marrons

Brown dwarfs are a very common type of object in our Galaxy, but due to their very low luminosity they rank among the hardest sources to detect. The known samples are still largely restricted to a distance of few tens of parsecs. Our motivation is to make a first large scale census of L and T dwarfs in order to study structural Milky Way parameters and to constrain the properties and formation history of this population. In order to do so, we developed a color selection method for brown dwarfs and applied it to large survey data. Our color selection was based on DES+VHS+WISE photometry. We also used these data for spectral classification of MLT dwarfs, by developing and applying a code that compares their observed colours to expected template values, with the minimization of the χ 2 . With the L and T dwarfs candidate sample in hand, we measured the scale height of disk L- type dwarfs. The L dwarf scale height was estimated with the aid of a brown dwarf simulation code, which we call GalmodBD , by comparing the observed and simulated number counts of such objects for a grid of models of varying spatial distributions. The initial estimate of scale height was h z,thin ∼ 450 parsec. We also studied benchmark systems, specifically the wide binary systems made up of L or T dwarfs orbiting main sequence stars. These systems are useful to improve brown dwarf evolutionary models, since their chemical composition and age constraints may be taken from the primary star assuming that the pair formed from the same gas cloud and at the same time. Our approach was to use our sample of brown dwarfs candidates selected from DES+VHS+WISE data and then search for possible companions in the Gaia DR2 and DES DR1 stellar data. We also searched for L and T dwarfs binary systems among themselves. We found 197 new binary systems made up by an L or T dwarf orbiting a main sequence star or in a double LT system and we also found 2 multiple system candidates, triple and quadru We found 197 new binary systems made up by an L or T dwarf orbiting a main sequence star or in a double LT system and we also found 2 multiple system candidates, triple and quadruple. All the systems with < 10,000 AU projected separation.Anãs marrons são um tipo comum de objeto na nossa Galáxia, mas devido á sua baixa luminosidade elas são fontes difícies de detectar. As amostras conhecidas ainda são em geral restritas a uma distância de poucas dezenas de parsecs. Nossa motivação é fazer um primeiro censo em grande escala de anãs L e T para então estudar parâmetros da Via Láctea e também restringir as propriedades e histórico da formação desta população. Para tal, nós desenvolvemos um método de seleção em cor para anãs marrons e o aplicamos a dados de grandes levantamentos. A seleção de cores foi feita usando a fotometria do DES+VHS+WISE. Usamos também os mesmos dados em um código de classificação espectral para anãs MLT, baseada na comparação das cores observadas e esperadas e minimização do χ2 . Com a amostra de candidatas a anãs L e T em mãos, nós medimos a escala de altura do disco para as anãs L. A escala de altura foi estimada com o auxílio de um código chamado GalmodBD , que simula anãs marrons, pela comparação entre a contagem observada e as simuladas para uma grade de modelos com diferentes distribuições espaciais. Nossa primeira estimativa da escala de altura do disco foi da ordem de hz, fino~450 pc. Também estudamos sistemas benchmark, especificamente em sistemas binários formados por uma anã L ou T orbitando uma estrela de sequência principal. Esses sistemas são úteis para melhorar modelos evolutivos de anãs marrons, dado que a composição química e idade podem ser obtidas através da estrela primária, assumindo que o par se formou de uma mesma nuvem de gás e ao mesmo tempo. Nossa abordagem foi usar nossa amostra de candidatas a anãs marrons selecionadas nos dados do DES+VHS+WISE e então procurar por possíveis companheiros nos dados do Gaia DR2 e da amostra estelar do DES DR1. Também procuramos por sistemas binários entre as próprias anãs L e T. Encontramos 197 novos sistemas binários constituídos por uma anã L ou T orbitando uma estrela de sequência principal ou em um sistema contituído por duas anãs marrons e encontramos 2 candidatos a sistemas múltiplos, um triplo e quádruplo. Todos os sistemas possuem uma separação projetada < 10,000 UA

Increasing the census of ultracool dwarfs in wide binary and multiple systems using Dark Energy Survey DR1 and Gaia DR2 data

We present the discovery of 255 binary and 6 multiple system candidates with wide (> 5 arcsec) separation composed by ultracool dwarfs (UCDs) companions to stars, plus nine double ultracool dwarf systems. These systems were selected based on common distance criteria. About 90 per cent of the total sample has proper motions available and 73 per cent of the systems also satisfy a common proper motion criterion. The sample of ultracool candidates was taken from the Dark Energy Survey (DES) and the candidate stellar primaries are from Gaia DR2 and DES data. We compute chance alignment probabilities in order to assess the physical nature of each pair. We find that 174 candidate pairs with Gaia DR2 primaries and 81 pairs with a DES star as a primary have chance alignment probabilities <5 per cent⁠. Only nine candidate systems composed of two UCDs were identified. The sample of candidate multiple systems is made up of five triple systems and one quadruple system. The majority of the UCDs found in binaries and multiples are of early L type and the typical wide binary fraction over the L spectral types is 2−4 per cent⁠. Our sample of candidate wide binaries with UCDs as secondaries constitutes a substantial increase over the known number of such systems, which are very useful to constrain the formation and evolution of UCD

Memórias das experiências com o brincar: narrativas e mônadas de professoras de educação infantil

The purpose of this work was to reflect on the memories of the experiences with the teachers’ playing that work in early childhood education, reconstructing, in the form of narratives and monads, the ludic universe lived by them. According to the perspective of oral history, three teachers from an early childhood education centre of a public university in São Paulo were interviewed. Reflecting on shared memories, we found that, as historical subjects immersed in a social reality, teachers have experiences with playing that are significant and constitute their singularity, reverberating in the way they see and mediate playing  in their teaching practice.El trabajo tuvo como objetivo reflexionar sobre las memorias de las experiencias con el jugar de profesoras que actúan en la educación infantil, reconstruyendo, en forma de narrativas y mónadas, el universo lúdico vivido por ellas. Tomando como referencia la perspectiva de la historia oral, fueron entrevistadas tres profesoras de un centro de educación infantil de una universidad pública paulista. A partir de las memorias compartidas, constatamos que, como sujetos históricos inmersos en una realidad social, las profesoras poseen experiencias con el jugar que son significativas y constituyen su singularidad, reverberando en la forma como las mismas ven y hacen la mediación del juego en su práctica docente.O trabalho teve como objetivo refletir sobre as memórias das experiências com o brincar de professoras que atuam na educação infantil, reconstruindo, em forma de narrativas e mônadas, o universo lúdico vivido por elas. Tomando como referência a perspectiva da história oral, foram entrevistadas três professoras de um centro de educação infantil de uma universidade pública paulista. Com base nas memórias compartilhadas, constatamos que, como sujeitos históricos imersos numa realidade social, as professoras possuem experiências com o brincar que são significativas e constituem sua singularidade, reverberando na forma como as mesmas veem e fazem a mediação das brincadeiras na sua prática docente

StarHorse: A Bayesian tool for determining stellar masses, ages, distances, and extinctions for field stars

Understanding the formation and evolution of our Galaxy requires accurate distances, ages and chemistry for large populations of field stars. Here we present several updates to our spectro-photometric distance code, that can now also be used to estimate ages, masses, and extinctions for individual stars. Given a set of measured spectro-photometric parameters, we calculate the posterior probability distribution over a given grid of stellar evolutionary models, using flexible Galactic stellar-population priors. The code (called {\tt StarHorse}) can acommodate different observational datasets, prior options, partially missing data, and the inclusion of parallax information into the estimated probabilities. We validate the code using a variety of simulated stars as well as real stars with parameters determined from asteroseismology, eclipsing binaries, and isochrone fits to star clusters. Our main goal in this validation process is to test the applicability of the code to field stars with known {\it Gaia}-like parallaxes. The typical internal precision (obtained from realistic simulations of an APOGEE+Gaia-like sample) are $\simeq 8\%$ in distance, $\simeq 20\%$ in age,$\simeq 6\$ in mass, and $\simeq 0.04$ mag in $A_V$. The median external precision (derived from comparisons with earlier work for real stars) varies with the sample used, but lies in the range of $\simeq [0,2]\%$ for distances, $\simeq [12,31]\%$ for ages, $\simeq [4,12]\%$ for masses, and $\simeq 0.07$ mag for $A_V$. We provide StarHorse distances and extinctions for the APOGEE DR14, RAVE DR5, GES DR3 and GALAH DR1 catalogues.Comment: 21 pages, 12 figures, accepte

StarHorse results for spectroscopic surveys + Gaia DR3: Chrono-chemical populations in the solar vicinity, the genuine thick disk, and young-alpha rich stars

The Gaia mission has provided an invaluable wealth of astrometric data for more than a billion stars in our Galaxy. The synergy between Gaia astrometry, photometry, and spectroscopic surveys give us comprehensive information about the Milky Way. Using the Bayesian isochrone-fitting code StarHorse, we derive distances and extinctions for more than 10 million unique stars observed by both Gaia Data Release 3 as well as public spectroscopic surveys: GALAH DR3, LAMOST DR7 LRS, LAMOST DR7 MRS, APOGEE DR17, RAVE DR6, SDSS DR12 (optical spectra from BOSS and SEGUE), Gaia-ESO DR5 survey, and Gaia RVS part of Gaia DR3 release. We use StarHorse for the first time to derive stellar age for main-sequence turnoff and subgiant branch stars (MSTO-SGB), around 2.5 million stars with age uncertainties typically around 30%, 15% for only SGB stars, depending on the resolution of the survey. With the derived ages in hand, we investigate the chemical-age relations. In particular, the $\alpha$ and neutron-capture element ratios versus age in the solar neighbourhood show trends similar to previous works, validating our ages. We use the chemical abundances from local subgiant samples of GALAH DR3, APOGEE DR17 and LAMOST MRS DR7 to map groups with similar chemical compositions and StarHorse ages with the dimensionality reduction technique t-SNE and the clustering algorithm HDBSCAN. We identify three distinct groups in all three samples. Their kinematic properties confirm them to be the genuine chemical thick disk, the thin disk and a considerable number of young alpha-rich stars. We confirm that the genuine thick disk's kinematics and age properties are radically different from those of the thin disk and compatible with high-redshift (z$\approx$2) star-forming disks with high dispersion velocities.Comment: 27 pages, 19 figures. Accepted for publication in Astronomy & Astrophysics. Catalogues can be downloaded at https://data.aip.de