3.10 Tesis magíster

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A search for substructures near the Galactic plane and bulge using RR Lyrae stars as tracers
(2024) Cristi Cambiaso, Nicolas Eduardo; Catelan, Marcio; Zoccali, Manuela; Pontificia Universidad Catolica de Chile. Faculty of Physics. Institute of Astrophysics
Usando estrellas pulsantes de tipo RR Lyrae, hacemos una búsqueda de subestructuras Galácticas ("stellar streams" y cúmulos globulares) en la región del plano Galáctico. Construimos una muestra de estrellas RR Lyrae con valores de distancia y metalicidades. Estudiamos esta muestra con un algoritmo de "clustering" para encontrar grupos de estrellas cercanas y con propiedades similares. Mediante esta búsqueda, recuperamos estructuras conocidas y encontramos posibles nuevas estructuras.
Chemistry in externally FUV illuminated protoplanetary disks in the Orion Nebula Cluster
(2022) Díaz Berríos, Javiera Katalina; Guzmán Veloso, Viviana; Pontificia Universidad Católica de Chile. Facultad de Física
Understanding the chemical composition and distribution of the birthplaces of planets (protoplanetary disks) is key to constraining the initial conditions of planet formation and planetary atmospheres. Most protoplanetary disks are born in stellar clusters and can therefore be affected by the radiation of nearby massive stars. However, little is known about the potential differences or similarities in the chemistry of isolated versus externally irradiated disks. Motivated by this question, we present ALMA Band 6 observations of two protoplanetary disks in the outskirts of the Orion Nebula Cluster (ONC) to explore the chemical composition of disks exposed to (external) FUV radiation fields: the large 216–0939 disk and the binary system 253–1536A/B. We successfully detect lines from CO isotopologues, HCN, H2CO, and C2H toward both protoplanetary disks. Undetected molecular lines include DCN and C3H2. Based on the observed disk–integrated line fluxes and flux, we do not find significant differences between isolated and irradiated disks. This suggests that these sources are far enough from the ONC so that their chemistry is not affected by the external radiation field or that we are observing the region from the disk that survives the external radiation; Indeed, these disks are massive and could, therefore self–shield from the radiation field. However, we expect CN emission to be brighter in irradiated disks than in isolated ones, which can be tested with future ALMA observations. We also expect stronger differences for disks that are closer to the ONC.
Contrasting neutron star heating mechanisms with Hubble Space Telescope observations
(2018) Rodríguez Tapia, Luis; Reisenegger, Andreas; Pontificia Universidad Católica de Chile. Instituto de Física
Si las estrellas de neutrones se enfriaran pasivamente, se esperaría que se vuelvan indetectables en un tiempo menor a 107 años, al alcanzar bajas temperaturas T < 104 K. Sin embargo, radiación del tipo ultravioleta, que implica temperaturas superficiales T ∼ 105 K, fue detectada desde los pulsares de Giga años PSR J0437- 4715 y PSR J2124-3358 y también desde el pulsar B0950+08 cuya edad es ∼ 107 años. Esta discrepancia puede ser explicada por un grupo de mecanismos de calentamiento propuestos en la literatura. Usando el código de Petrovich y Reisenegger se calcularon curvas de evolución térmica considerando diferentes mecanismos de calentamiento. Estas fueron contrastadas con las temperaturas inferidas a partir de las observaciones de los pulsares para determinar cuál es la principal fuente de emisión térmica de las estrellas de neutrones. Encontramos que el calentamiento rotoquímico, reacciones nucleares en las capas profundas de la corteza y el calor liberado por la fricción de vórtices superfluidos pueden mantener la estrella lo suficientemente caliente más allá del tiempo estándar de enfriamiento pasivo y explicar las observaciones.Si las estrellas de neutrones se enfriaran pasivamente, se esperaría que se vuelvan indetectables en un tiempo menor a 107 años, al alcanzar bajas temperaturas T < 104 K. Sin embargo, radiación del tipo ultravioleta, que implica temperaturas superficiales T ∼ 105 K, fue detectada desde los pulsares de Giga años PSR J0437- 4715 y PSR J2124-3358 y también desde el pulsar B0950+08 cuya edad es ∼ 107 años. Esta discrepancia puede ser explicada por un grupo de mecanismos de calentamiento propuestos en la literatura. Usando el código de Petrovich y Reisenegger se calcularon curvas de evolución térmica considerando diferentes mecanismos de calentamiento. Estas fueron contrastadas con las temperaturas inferidas a partir de las observaciones de los pulsares para determinar cuál es la principal fuente de emisión térmica de las estrellas de neutrones. Encontramos que el calentamiento rotoquímico, reacciones nucleares en las capas profundas de la corteza y el calor liberado por la fricción de vórtices superfluidos pueden mantener la estrella lo suficientemente caliente más allá del tiempo estándar de enfriamiento pasivo y explicar las observaciones.
High-Cadence Stellar Variability Studies of Galactic RR Lyrae Stars with DECam
(2023) Baeza Villagra, Karina; Catelan, Márcio; Pontificia Universidad Católica de Chile. Facultad de Física
As part of the DECam Alliance for Transients (DECAT), a consortium of time- domain DECam programs, the DECam Deep Drilling Program (DDP) is being conducted at the Blanco 4m telescope, located at Cerro Tololo Inter-American Observatory, Chile. The DDP includes the DECaPS East field, situated in the Galactic bulge at coordinates (RA, DEC)(J2000) = (18:03:34, -29:32:02). We performed two nights of high-cadence, multi- band (griz) observations utilizing DECam. We obtained high-quality griz light curves for 1033 previously identified RR Lyrae stars. Subsequently, a robust Fourier decomposition analysis was con- ducted, generating well-defined, multi-band light curve templates for 143 RRab and 146 RRc stars. This process aimed to update and enhance the existing RR Lyrae star templates catalog. Therefore, our work is expected to broadly apply to the data acquired from the Vera C. Rubin Observatory’s Legacy Survey of Space and Time. Furthermore, we compared and analyzed the dependence of Fourier coef- ficients and other derived light curve parameters on the effective wavelength, providing valuable in-sights into the behavior and structure of RR Lyrae stars. Another significant contribution of this study was the construction of the Period- φ31-[Fe/H] relations, total-to-selective extinction ratios, and distances for each star in both the DECam and Sloan photometric systems. This information is crucial for investigating RR Lyrae stars and their role as tracers of Galactic structures. By combining these results, we better un- derstand the characteristics and morphology of their light curves, the chemical composition through studying their metallicities, and the spatial distribution of RR Lyrae stars within the Galactic bulge. This knowledge contributes to the overall effort of classifying and detecting variable stars.
Magneto-thermal evolution of neutron star cores in the “strong-coupling regime”
(2020) Moraga Vent, Nicolás Andrés; Reisenegger, Andreas; Pontificia Universidad Católica de Chile. Instituto de Física
In this thesis we study a young neutron star, with internal temperatures T >10^9 K, where the particles in the core are strongly coupled by collisional forces and can convert into each other by beta decays, in the so called ``strong-coupling regime``. At this stage, the magnetic field induces small fluid displacements, changing the local chemical composition and generating pressure gradient forces, which tend to be erased by beta decays. Depending on the strength of the chemical departure, this reactions can lead to a non-trivial thermal evolution as a consequence of the magnetic feedback. This mechanism converts magneticto thermal energy and could explain the high surface luminosity of magnetars (highly magnetize neutron stars). In this thesis, we present the first long-term magneto-thermal simulation of a neutron star core in this regime. We concluded that, for internal magnetic field strength field B > 10^16 G, the possibility of a magnetic feedback due to the chemical departure is not possible because it would occur when the ambipolar heating (friction between charged particles and neutrons) is more likely to heat the core.
Metallicities and ages in the red sequence of two clusters of galaxies
(2022) Muñoz López, Constanza Betzabé; Barrientos, Luis Felipe; Pontificia Universidad Católica de Chile. Facultad de Física
Esta tesis se centra principalmente en las propiedades de las galaxias de secuencia roja y qué pueden decirnos estos parámetros acerca de las características y los procesos de formación de las galaxias. Las galaxias de tipo temprano (early-type) ofrecen la oportunidad de estudiar la formación y evolución de poblaciones estelares. Mediante el uso de fotometría proveniente del HST y datos espectroscópicos telescopio VLT/MUSE de dos cúmulos de galaxias, ha sido posible analizar edades y metalicidades de las galaxias y compararlas con otros observables. Se creó un modelo de secuencia roja para ambos cúmulos y se estableció una conexión entre las edades de las galaxias y sus respectivo desplazamiento con la secuencia roja. Las observaciones de este trabajo sugieren que la mayoría de las galaxias comenzaron a formar sus poblaciones estelares cuando el Universo era joven (z> 3) y que ya tenían acumulada más del 80% de su masa a z = 2. Sin embargo, no contamos con la sensibilidad suficiente para establecer el momento exacto en que comenzaron los procesos de formación estelar.
New insights and methods for the clustering of emission line galaxies.
(2019) Jiménez Henríquez, Esteban; Padilla, Nelson; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
We study the dependence of emission line galaxies (ELG) clustering in halo properties besides mass, an effect known as assembly bias (AB). This AB signature is scale-dependent in some ELG samples and may contribute with potential systematic effects on cosmology constraints. We test different implementations of the halo occupation distribution (HOD) model to construct mock galaxy catalogues that mimic ELG selected samples produced by a semi-analytical model (SAM). These catalogues are useful to understand the future observational samples. We select galaxies from two different SAMs, applied to the Millennium-WMAP7 and the MultiDark Plank 2 simulation. We use fixed number density galaxy samples selected according to stellar mass, star formation rate (SFR), and emission line luminosity from Hα, [OIII]λ5007, and [OII]λλ3727 − 3729 emission, obtained from a photoionization code. We develop three different schemes to populate haloes with galaxies with increasing complexity, considering the scatter of the satellites HOD as an additional parameter in the modellings. The quality of the HOD modelling is determined by comparing the two-point correlation function (2PCF) of the HOD mocks and the SAM samples. The HOD modelling that uses the HOD of centrals and satellites separately, and assume a negative binomial distribution for the satellite HOD, produce the best clustering predictions. The scatter in the satellites HOD is a key consideration for HOD mock catalogues that mimic ELG selected samples in future galaxy surveys. The origin of the scale-dependent AB seems to be related to an environment selection effect rather than a physical reason. We found that galaxies in underdense regions and low gas metallicity, make the main contribution to the scale-dependent signature. We obtain that the peak of the Baryon Acoustic Oscillation (BAO) for some ELG samples is in lower scales than expected, and the β parameter is non-constant in large scales. Hence, this selection effect can introduce systematic in the inferred cosmology from ELGs.
Thermodynamics of graviton condensate and the Kiselev black hole
(2020) Mancilla Pérez, Robinson Humberto; Alfaro Solís, Jorge Luis; Pontificia Universidad Católica de Chile. Instituto de Física
In this thesis, we will present the thermodynamic study of a model that considers the black hole as a condensation of gravitons (55) (56). We will obtain a correction to the Hawking temperature and a negative pressure for a black hole of mass M. In this way, the graviton condensate, which is assumed to be at the critical point defined by the condition µch=0, will have well-defined thermodynamic quantities P, V , Th, S, and U as any other Bose-Einstein condensate. We will also discuss the Kiselev black hole, which has the capacity to parametrize the most well-known spherically symmetric black holes. We will show that this is true, even at the thermodynamic level. Finally, we will present a new metric, which we will call the BEC-Kiselev black hole, that will allow us to extend the graviton condensate to the case of solutions with different types of the energy-momentum tensor.In this thesis, we will present the thermodynamic study of a model that considers the black hole as a condensation of gravitons (55) (56). We will obtain a correction to the Hawking temperature and a negative pressure for a black hole of mass M. In this way, the graviton condensate, which is assumed to be at the critical point defined by the condition µch=0, will have well-defined thermodynamic quantities P, V , Th, S, and U as any other Bose-Einstein condensate. We will also discuss the Kiselev black hole, which has the capacity to parametrize the most well-known spherically symmetric black holes. We will show that this is true, even at the thermodynamic level. Finally, we will present a new metric, which we will call the BEC-Kiselev black hole, that will allow us to extend the graviton condensate to the case of solutions with different types of the energy-momentum tensor.In this thesis, we will present the thermodynamic study of a model that considers the black hole as a condensation of gravitons (55) (56). We will obtain a correction to the Hawking temperature and a negative pressure for a black hole of mass M. In this way, the graviton condensate, which is assumed to be at the critical point defined by the condition µch=0, will have well-defined thermodynamic quantities P, V , Th, S, and U as any other Bose-Einstein condensate. We will also discuss the Kiselev black hole, which has the capacity to parametrize the most well-known spherically symmetric black holes. We will show that this is true, even at the thermodynamic level. Finally, we will present a new metric, which we will call the BEC-Kiselev black hole, that will allow us to extend the graviton condensate to the case of solutions with different types of the energy-momentum tensor.In this thesis, we will present the thermodynamic study of a model that considers the black hole as a condensation of gravitons (55) (56). We will obtain a correction to the Hawking temperature and a negative pressure for a black hole of mass M. In this way, the graviton condensate, which is assumed to be at the critical point defined by the condition µch=0, will have well-defined thermodynamic quantities P, V , Th, S, and U as any other Bose-Einstein condensate. We will also discuss the Kiselev black hole, which has the capacity to parametrize the most well-known spherically symmetric black holes. We will show that this is true, even at the thermodynamic level. Finally, we will present a new metric, which we will call the BEC-Kiselev black hole, that will allow us to extend the graviton condensate to the case of solutions with different types of the energy-momentum tensor.In this thesis, we will present the thermodynamic study of a model that considers the black hole as a condensation of gravitons (55) (56). We will obtain a correction to the Hawking temperature and a negative pressure for a black hole of mass M. In this way, the graviton condensate, which is assumed to be at the critical point defined by the condition µch=0, will have well-defined thermodynamic quantities P, V , Th, S, and U as any other Bose-Einstein condensate. We will also discuss the Kiselev black hole, which has the capacity to parametrize the most well-known spherically symmetric black holes. We will show that this is true, even at the thermodynamic level. Finally, we will present a new metric, which we will call the BEC-Kiselev black hole, that will allow us to extend the graviton condensate to the case of solutions with different types of the energy-momentum tensor.In this thesis, we will present the thermodynamic study of a model that considers the black hole as a condensation of gravitons (55) (56). We will obtain a correction to the Hawking temperature and a negative pressure for a black hole of mass M. In this way, the graviton condensate, which is assumed to be at the critical point defined by the condition µch=0, will have well-defined thermodynamic quantities P, V , Th, S, and U as any other Bose-Einstein condensate. We will also discuss the Kiselev black hole, which has the capacity to parametrize the most well-known spherically symmetric black holes. We will show that this is true, even at the thermodynamic level. Finally, we will present a new metric, which we will call the BEC-Kiselev black hole, that will allow us to extend the graviton condensate to the case of solutions with different types of the energy-momentum tensor.In this thesis, we will present the thermodynamic study of a model that considers the black hole as a condensation of gravitons (55) (56). We will obtain a correction to the Hawking temperature and a negative pressure for a black hole of mass M. In this way, the graviton condensate, which is assumed to be at the critical point defined by the condition µch=0, will have well-defined thermodynamic quantities P, V , Th, S, and U as any other Bose-Einstein condensate. We will also discuss the Kiselev black hole, which has the capacity to parametrize the most well-known spherically symmetric black holes. We will show that this is true, even at the thermodynamic level. Finally, we will present a new metric, which we will call the BEC-Kiselev black hole, that will allow us to extend the graviton condensate to the case of solutions with different types of the energy-momentum tensor.In this thesis, we will present the thermodynamic study of a model that considers the black hole as a condensation of gravitons (55) (56). We will obtain a correction to the Hawking temperature and a negative pressure for a black hole of mass M. In this way, the graviton condensate, which is assumed to be at the critical point defined by the condition µch=0, will have well-defined thermodynamic quantities P, V , Th, S, and U as any other Bose-Einstein condensate. We will also discuss the Kiselev black hole, which has the capacity to parametrize the most well-known spherically symmetric black holes. We will show that this is true, even at the thermodynamic level. Finally, we will present a new metric, which we will call the BEC-Kiselev black hole, that will allow us to extend the graviton condensate to the case of solutions with different types of the energy-momentum tensor.In this thesis, we will present the thermodynamic study of a model that considers the black hole as a condensation of gravitons (55) (56). We will obtain a correction to the Hawking temperature and a negative pressure for a black hole of mass M. In this way, the graviton condensate, which is assumed to be at the critical point defined by the condition µch=0, will have well-defined thermodynamic quantities P, V , Th, S, and U as any other Bose-Einstein condensate. We will also discuss the Kiselev black hole, which has the capacity to parametrize the most well-known spherically symmetric black holes. We will show that this is true, even at the thermodynamic level. Finally, we will present a new metric, which we will call the BEC-Kiselev black hole, that will allow us to extend the graviton condensate to the case of solutions with different types of the energy-momentum tensor.In this thesis, we will present the thermodynamic study of a model that considers the black hole as a condensation of gravitons (55) (56). We will obtain a correction to the Hawking temperature and a negative pressure for a black hole of mass M. In this way, the graviton condensate, which is assumed to be at the critical point defined by the condition µch=0, will have well-defined thermodynamic quantities P, V , Th, S, and U as any other Bose-Einstein condensate. We will also discuss the Kiselev black hole, which has the capacity to parametrize the most well-known spherically symmetric black holes. We will show that this is true, even at the thermodynamic level. Finally, we will present a new metric, which we will call the BEC-Kiselev black hole, that will allow us to extend the graviton condensate to the case of solutions with different types of the energy-momentum tensor.

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