Search, Spectral Classification and Benchmarking of Brown Dwarfs
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UNIVERSIDADE FEDERAL DO RIO GRANDE DO SUL INSTITUTO DE F´ISICA DEPARTAMENTO DE ASTRONOMIA Search, spectral classification and benchmarking of brown dwarfs Marina Dal Ponte Msc. dissertation taken under the super- vision of Dr. Bas´ılioXavier Santiago sub- mitted to the Graduate Program of Insti- tuto de F´ısica- Universidade Federal do Rio Grande do Sul (UFRGS) as part of the fulfilment to obtain the master's degree in physics with emphasis in astrophysics. Porto Alegre, RS, Brasil 2019 ? This work has received financial support from Coordena¸c~aode Aperfei¸coamento de Pessoal de N´ıvel Superior (CAPES) UNIVERSIDADE FEDERAL DO RIO GRANDE DO SUL INSTITUTO DE F´ISICA DEPARTAMENTO DE ASTRONOMIA Procura, classifica¸c~aoespectral e benchmarking de an~asmarrons Marina Dal Ponte Porto Alegre, RS, Brasil 2019 ? Trabalho financiado pela Coordena¸c~aode Aperfei¸coamento de Pessoal de N´ıvel Superior (CAPES) "There's comfort in melancholy When there's no need to explain It's just as natural as the weather In this moody sky today" Joni Mitchell (Hejira,1976.) Acknowledgements To my family, especially my mother Zenaide and father Santo, for all the sup- port. Even though my life choice was the oddest for them, it was fundamental never being questioned for my decisions. I also appreciate all their curiosity related to my work and the pride in their voices when referring to me as the scientist of the family. To my advisor, Bas´ılioXavier Santiago for all the patience, the sharing of knowl- edge, the teaching of how to question, for all the trust and support in difficult times and all the efforts that made me grow as a researcher. To my astro friends Anna, Lari, Nicolas, Ale, Ingrid, Fernanda for all the sup- port, for encouraging me in life and work and for all the beer nights. An extra special thanks for the astro girls, who always share their amazing power with me. To the people of M207, especially Amanda and Vinicius, for providing lots of coffee every single day. Also thanks for the chocolate, cake, bread and caipirinha. Also an extra thanks to Vini, my bike partner, who taught me how to be nicer and gentle with car drivers even when they don't deserve. To my friend Gabrielly, a true sister, and Nick for sharing so much so fast. We learn a lot together and I feel really privileged having you in my life. To my boyfriend Fabio for being there in the most stressful and anxious moments of my life. Thanks a lot for helping me and for constantly trying to convince me that everything is going to be ok. To Aurelio for the amazing brown dwarfs journey, for the patience, all the shared tasks and knowledge and for encouraging me to move forward. All of my life I studied in public institutions and without them, I wouldn't be able to be where I am today. We must support quality public education to provide all kinds of opportunities to people who wouldn't have them otherwise. Abstract 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 χ2. 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 hz;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 quadruple. All the systems with < 10,000 AU projected separation. Key-words: Brown Dwarfs, Benchmarks, Dark Energy Survey Resumo An~asmarrons s~aoum tipo comum de objeto na nossa Gal´axia,mas devido `a sua baixa luminosidade elas s~aofontes dif´ıciesde detectar. As amostras conhecidas ainda s~aoem geral restritas a uma dist^anciade poucas dezenas de parsecs. Nossa motiva¸c~ao´efazer um primeiro censo em grande escala de an~asL e T para ent~ao estudar par^ametrosda Via L´acteae tamb´emrestringir as propriedades e hist´oricoda forma¸c~aodesta popula¸c~ao.Para tal, n´osdesenvolvemos um m´etodo de sele¸c~aoem cor para an~asmarrons e o aplicamos a dados de grandes levantamentos. A sele¸c~ao de cores foi feita usando a fotometria do DES+VHS+WISE. Usamos tamb´emos mesmos dados em um c´odigode classifica¸c~aoespectral para an~asMLT, baseada na compara¸c~aodas cores observadas e esperadas e minimiza¸c~aodo χ2. Com a amostra de candidatas a an~asL e T em m~aos,n´osmedimos a escala de altura do disco para as an~asL. A escala de altura foi estimada com o aux´ıliode um c´odigochamado GalmodBD, que simula an~asmarrons, pela compara¸c~aoentre a contagem observada e as simuladas para uma grade de modelos com diferentes distribui¸c~oesespaciais. Nossa primeira estimativa da escala de altura do disco foi da ordem de hz;fino ∼ 450 pc. Tamb´emestudamos sistemas benchmark, especificamente em sistemas bin´arios formados por uma an~aL ou T orbitando uma estrela de sequ^enciaprincipal. Esses sistemas s~ao´uteispara melhorar modelos evolutivos de an~asmarrons, dado que a composi¸c~aoqu´ımicae idade podem ser obtidas atrav´esda estrela prim´aria,assu- mindo que o par se formou de uma mesma nuvem de g´ase ao mesmo tempo. Nossa abordagem foi usar nossa amostra de candidatas a an~asmarrons selecionadas nos dados do DES+VHS+WISE e ent~aoprocurar por poss´ıveis companheiros nos dados do Gaia DR2 e da amostra estelar do DES DR1. Tamb´emprocuramos por sistemas bin´ariosentre as pr´opriasan~asL e T. Encontramos 197 novos sistemas bin´arios constitu´ıdospor uma an~aL ou T orbitando uma estrela de sequ^enciaprincipal ou em um sistema contitu´ıdopor duas an~asmarrons e encontramos 2 candidatos a sis- temas m´ultiplos,um triplo e qu´adruplo.Todos os sistemas possuem uma separa¸c~ao projetada < 10,000 UA. Palavras-chaves: An~as marrons, Benchmarks, Dark Energy Survey Contents Contents 1 1 Introduction 2 1.1 Brief history of brown dwarfs . .2 1.2 Brown dwarfs properties and characteristics . .3 1.3 Evolutionary models . .4 1.4 Luminosity and Mass Function . .8 1.5 Spectroscopic and photometric samples of L, T and Y dwarfs . .9 1.6 Benchmark brown dwarfs . 11 1.7 L and T dwarfs and the Dark Energy Survey . 12 2 DES L and T dwarfs sample 14 3 Benchmark L and T dwarfs 43 4 Conclusions and Future Perspectives 61 References 63 1 Chapter 1 Introduction 1.1 Brief history of brown dwarfs The existence of objects with a mass less that a certain limit that cannot burn hydrogen because of their temperature and density was demonstrated by Kumar (1963), based on theoretical calculations. Instead, the object contracts, becomes completely degenerate and the electron degeneracy pressure provides the hydrostatic equilibrium. The hydrogen burning minimum mass of mHBMM ∼ 0:085M was proposed by Grossman et al. (1974) based on detailed evolutionary calculations, however the term brown dwarf was given by Tarter (1975) to designate such objects. The firsts discoveries of bona fide brown dwarfs were made only in the 1990s. Gliese 229B, shown in Figure 1.1, discovered by Oppenheimer et al. (1995), exhibited a strong methane (CH4) absorption line which implied an object too cool to be a star. Also, in the Pleiades cluster, PP1 15 and Teide 1 (Stauffer et al., 1994, Rebolo et al., 1995) were identified as promising brown dwarfs candidates and were confirmed later by the detection of lithium (Li) (see Section 1.2), therefore becoming the first known free-floating brown dwarfs. The early models for low mass stars and brown dwarfs suggested by Vandenberg et al. (1983), Dantona & Mazzitelli (1985), Nelson et al. (1986), Lunine et al. (1986), Burrows et al. (1989), Dorman et al. (1989) failed to reproduce the observations at the bottom of the Main Sequence (MS) and to provide a reliable determination of properties such as mass, age, effective temperature (Teff ) and luminosity.