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A Relationship Between Iron Spread and Variability in Giant Stars Of UNIVERSIDAD DE CONCEPCIÓN FACULTAD DE CIENCIAS FÍSICAS Y MATEMÁTICAS PROGRAMA DE MAGÍSTER EN ASTRONOMÍA A RELATIONSHIP BETWEEN IRON SPREAD AND VARIABILITY IN GIANT STARS OF GLOBULAR CLUSTERS (UNA RELACIÓN ENTRE DISPERSIÓN DE HIERRO Y VARIABILIDAD EN ESTRELLAS GIGANTES DE CÚMULOS GLOBULARES) Profesor Guía: Dr. Sandro Villanova Departamento de Astronomía Facultad de Ciencias Físicas y Matemáticas Universidad de Concepción Tesis para ser presentada a la Dirección de Postgrado de la Universidad de Concepción para optar al grado de Magister en Astronomía ÁLVARO IGNACIO LLANCAQUEO ALBORNOZ Concepción - Chile Enero 2020 III Acknowledgements Primero que todo quiero agradecer a mi profesor guía, Dr. Sandro Villanova por su guianza, su apoyo durante estos años y por haberme aceptado como su estu- diante para este programa. Quiero agradecer además a Caddy Cortés, por haberme ayudado a lo largo de este tiempo, guiando y ayudándome en mi trabajo, otorgando comentarios, destacando los errores que tenía y dándome sugerencias sobre cómo avanzar en este trabajo Por apoyarme tanto emocionalmente para seguir adelante en tiempos difíciles, su apoyo económico para que haya podido seguir estudiando en la Universidad de Concepción y más importante por tener fe en mí, quiero agradecer a mis padres Álvaro Llancaqueo Valeri y Edith Albornoz Rojas. Por su apoyo y guía cuando tenia dudas relacionadas en cómo seguir y al practi- car mis presentaciones, agradezco a mi profesora de Lenguaje de The Wessex School y amiga, Pamela Cebrero. Quiero también darle las gracias a mis amigos de las comunidades “Yu-Gi-Oh! TCG” y “Cardfight!! Vanguard” de Concepción, en especial a Felipe Jarpa, Eduar- do Ramirez, Carlos Becar, Hernán Rodriguez, Matias Valeria, Diego Soto, Mauricio Werlinger y Pablo Flores. Por su apoyo emocional, amistad y camaradería, además de escucharme de vez en cuando cuando hablaba de mi trabajo. También agradezco a todos mis colegas, compañeros y miembros del Departa- mento de Astronomía de la Universidad de Concepción por su ayuda y contribu- ciones varias, especialmente durante el último año del programa. Quiero hacer una mención especial a mis amigos que estuvieron conmigo durante mi formación aca- démica en pregrado desde el 2014 al 2017: Matias Cruces, Juan Arévalo y Javier Henríquez. Por último quiero darle las gracias a aquellos que colaboraron en este trabajo, Javier Ahumada y Celeste Parisi, especialmente al equipo de trabajo de Javier por habernos otrogado los datos, siendo estos las curvas de luz de las estrellas, el CMD y las imágenes del cúmulo, los cuales fueron usados para este trabajo, además de agradecer al staff de PyAstronomy dado que gran parte de los resultados obtenidos en este trabajo fueron hecho con su software, además de responder mis dudas respecto a cómo funcionaban algunos de sus módulos. V UNIVERSIDAD DE CONCEPCIÓN Abstract Facultad de Ciencias Físicas y Matemáticas Departmento de Astronomía BSc. in Astronomy A relationship between iron spread and variability in giant stars of globular clusters by Álvaro LLANCAQUEO The work presented here is the results from an analysis of 34 light curves, 17 in the V filter and 17 in the I filter of 17 giant stars of NGC 3201, spanning 4 nights of observation carried out on March 20-23, 2013. The objective of this work was to check and prove if there is a relationship be- tween the variability of a giant star and its iron abundance. To analyze the light curves the Generalized Lomb-Scargle periodogram and the Phase Dispersion Min- imization method were computed, and used in order to check if each giant was a variable star. Then a revision of the [Fe/H] values of each variable star from the literature was carried out. From the period analysis made in the sample of 17 stars, 8 were non-variable, 3 were considered as possible variables and 6 stars were variable. From the sam- ple of the discovered variable stars, they displayed different periods ranging from 0.0881 ± 0.0001 to 0.5418 ± 0.0027 days. These 6 variable stars showed distinct values of [Fe I/H], the 3 most metal-rich stars being RGB, one star with [Fe I/H] = −1.37 and two with [Fe I/H] = −1.31 dex. The two most metal-poor variables have [Fe I/H] = −1.61 and [Fe I/H] = −1.62 dex and are AGB stars and one variable showed [Fe I/H] = −1.50 dex also being an AGB star. Meanwhile stars that were non-variables showed −1.56 ≤ [Fe I/H] ≤ −1.40. The conclusion brought from this work is that there is a relationship between the iron abundance and variability of giant stars, where stars that are variable present extreme values [Fe/H] compared with the stars that are non-variable and that vari- ability affects somehow the spectroscopic determination of the iron content of giant stars in globular clusters. VII UNIVERSIDAD DE CONCEPCIÓN Resumen Facultad de Ciencias Físicas y Matemáticas Departmento de Astronomía BSc. in Astronomy A relationship between iron spread and variability in giant stars of globular clusters by Álvaro LLANCAQUEO El trabajo presentado es el resultado del análisis de 34 curvas de luz, 17 en el filtro V y 17 en el filtro I de 17 estrellas gigantes de NGC 3201, cubriendo 4 noches de observación realizadas en Marzo 20-23, 2013. El objetivo de este trabajo fue checkear y probar si hay una relación entre la va- riabilidad de una estrella y su abundancia de hierro. Para analizar las curvas de luz se utilizaron los métodos “Generalized Lomb-Scargle periodogram” y “Phase Dis- persion Minimization”, con el fin de ver si cada estrella gigante era una variable. Luego, se realizó una revisión de los valores de [Fe/H] de cada estrella variable en la literatura. Del análisis de período realizado en la muestra de 17 estrellas, 8 eran no varia- bles, 3 fueron consideradas como posibles variables y 6 estrellas eran variables. De la muestra de estrellas variables descubiertas, mostraban diferentes períodos que van desde los 0,0881 ± 0,0001 hasta los 0,5418 ± 0,0027 días. Además, estas 6 estrellas variables mostraban valores de [Fe I/H] distintivos, las 3 estrellas más “metal-rich” eran RGB, una de ellas con [Fe I/H] = −1,37 y dos con [Fe I/H] = −1,31 dex. Las dos variables más “metal-poor” tienen [Fe I/H] = −1,61 y [Fe I/H] = −1,62 dex y son estrellas AGB y una variable mostraba un [Fe I/H] = −1,50 dex siendo tam- bién una estrella AGB. Mientras tanto, las estrellas que no son variables mostraban −1,56 ≤ [Fe I/H] ≤ −1,40. La conclusión que se obtuvo de este trabajo es que sí hay una relación entre la abundancia de hierro y la variabilidad de las estrellas gigantes, en donde las estre- llas que son variables presentan valores extremos de [Fe/H] comparado con aquellas estrellas que no lo son, además que la variabilidad afecta de alguna manera la deter- minación espectroscópica del contenido de hierro en estrellas gigantes en cúmulos globulares IX Contents Acknowledgements III Abstract V 1. Introduction and Context1 1.1. Overview of Globuar Clusters........................1 1.2. Stellar Evolution................................2 1.2.1. The Hertzsprung-Russell Diagram.................2 The Color-Magnitude Diagram...................2 1.2.2. The Formation of a Star.......................5 1.2.3. Hydrostatic Equilibrium of Stars..................5 1.2.4. Virial Theorem for Stellar Evolution Theory...........6 1.3. Post-Main Sequence Stars..........................8 1.3.1. Red Giant Branch...........................9 Low-mass star evolution....................... 11 Intermediate and high-mass star evolution............ 11 1.3.2. Horizontal Branch.......................... 12 1.3.3. Asymptotic Giant Branch...................... 12 1.4. Metallicity................................... 14 1.4.1. Determining stellar composition using mass fraction...... 14 1.4.2. Determination of chemical abundance ratios........... 15 1.5. Chemical characteristics of Globular Clusters............... 15 1.5.1. The Metallicity Distribution in Globular Clusters........ 17 1.6. Variable Stars................................. 19 1.6.1. Pulsating Stars............................ 20 Pulsating Red Giants......................... 20 The classification of pulsating red giants............. 21 2. Is there a relationship between variability and iron abundance? 23 2.1. A metal-poor variable RGB star in NGC 6528............... 23 2.2. Objectives of this investigation....................... 24 2.2.1. General Objectives.......................... 24 2.2.2. Specific Objectives.......................... 24 X 3. Previous investigations of NGC 3201 25 3.1. General information of NGC 3201...................... 25 3.2. The dubious intrinsic iron spread of NGC 3201.............. 26 3.3. Latest results regarding the iron abundance of NGC 3201........ 27 3.4. A new approach to study NGC 3201.................... 28 4. The Generalized Lomb-Scargle and Phase Dispersion Minimization Meth- ods 29 4.1. The Generalized Lomb-Scargle periodogram............... 29 4.1.1. False Alarm Probability....................... 30 4.2. The Phase Dispersion Minimization method............... 30 4.2.1. Definitions and characteristics of the PDM method........ 31 4.3. The PyAstronomy package colletion..................... 32 4.3.1. The GLS class ............................. 32 API documentation of the GLS class................ 32 4.3.2. The PyPDM class ........................... 33 Parameters of Scanner and PyPDM ................. 34 5. Relation of [Fe/H] & variability in giant stars of NGC 3201? 35 5.1. Abstract.................................... 35 5.2. General Information of the data....................... 36
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