Tesis postgrado Astrofísica

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Examinando Tesis postgrado Astrofísica por Materia "ESTRELLAS MULTIPLES"

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  • Miniatura
    Ítem
    Análisis de la relación momentum luminosidad en estrellas masivas
    (Universidad de Valparaíso, 2022-05-03) Machuca Arroyo, Natalia; Curé, Michel
    La teoría de los vientos impulsados por radiación predice una relación entre el momentum del viento y la luminosidad estelar (Dmom ∝ L*). Sin embargo, esta relación parece variar en función del tipo espectral. El momentum del viento es proporcional a la velocidad terminal del viento v∞, la tasa de pérdida de masa M˙ , y al radio estelar R*1/2. En esta tesis, buscamos estudiar por primera vez la relación momentum luminosidad del viento (WLR, por sus siglas en inglés) usando la hidrodinámica de manera consistente en los cálculos NLTE de transporte radiativo. Desarrollamos un código que usa un testeo de χ2 para determinar el modelo que mejor se ajusta a las líneas espectrales SiIII (4552), HeI (4471 y 6678 ˚A), Hγ, Hβ y Hα observadas de 17 estrellas tipo OB de la grilla ISOSCELES. Esta grilla está basada en el código hidrodinámico HYDWIND y el código FASTWIND de transferencia radiativa NLTE. En esta tesis se ha encontrado que la solución δ-slow, recrea de buena manera las lineas espectrales de 8 de las 17 estrellas analizadas. Las soluciones encontradas con este método, entregan además un perfil de velocidad distinto a las aproximaciones que usan ley β. Se han encontrado también, nuevos resultados para la WLR, por primera vez consistentes con la hidrodinámica que rige los vientos, y que además predicen una dependencia en el tipo de solución hidrodinámica.
  • Miniatura
    Ítem
    Determination of stellar parameters of rapidly rotating massive stars
    (Universidad de Valparaíso, 2023-03) Turis Gallo, Daniela; Supervisor: Cure, Michael; Co-supervisor: Arcos, Catalina; External reviewer: Levenhagen, Ronaldo
    Fast rotation directly affects the shape of the observed spectral lines. Therefore, sev- eral physical considerations must be considered when using stellar atmosphere mod- els to obtain stellar parameters. In this work, we used the code ZPEKTR, which con- siders the oblate shape of the stars due to the high rotational velocities, limb darken- ing, and gravity darkening effects. The code divides the stellar surface into a triangu- lar mesh with approximately 120000 area elements. Each one is assigned a TLUSTY model with its effective temperature, log g, and radius; the model depends on the in- clination angle of the star. We applied this code to obtain the stellar parameters of ten classical Be stars and two extremely metal-poor O stars. We create a grid of models for each star and use the chi-square test to determine the best fit to the observed HeI 4471A˚ (Be stars) and CIII 1176A˚ (O stars) spectral lines. Comparing our results of the inclination angle with data from the literature obtained using interferometry, we can conclude that with a small telescope and using spectroscopic techniques, we can find an accurate value for i. For future work, we will use the code for many fast-rotating stars and increase the number of photospheric lines used.
  • Miniatura
    Ítem
    Identifying and characterising post-encounter disintegrating system
    (Universidad de Valparaíso, 2023-07) Ka Po Yip, Alexandra; Kurtev, Radostin
    Disintegrating multiple systems are thought to be very common based on numerical simulations, which predict that 50% to 95% of non-hierarchical triple systems and 10% of hierarchical triple systems undergo an ejection at some point in their evolution. However, very few of these systems have so far been observed. Kinematic studies of the Hipparcos catalogue have revealed only 10 disintegrating triple candidates. They are presumably the result of dynamical encounters taking place in the Galactic disk between single/multiple systems. In this thesis, I expanded the search for such systems to study their properties, as well as to characterize possible low-mass ejecta (i.e. brown dwarfs and planets). I have assembled a list of 20 candidate systems using astrometry from the Tycho-Gaia astrometric solution (later upgraded with Gaia DR3), and here I present the follow-up of 9 of them. I have obtained medium-resolution spectra for 4 of them and used the spectra to determine their radial velocity and metallicity. These measurements allowed me to conclude that two of the systems observed with ISIS are likely genuine disintegrating systems, for which I have reconstructed the most probable interaction scenario. I have obtained DECam imaging for 5 systems and by combining near-infrared photometry and proper motion, I searched for ultra- cool ejected components. I found that the system consisting of TYC 7731-1951-1, TYC 7731-2128-1 AB, and TYC 7731-1995-1ABC?, contains one very promising ultra-cool dwarf candidate. Using additional data from the literature, I have found that 3 out of the 5 disintegrating system candidates observed with DECam are likely to be true dis- integrating systems. Overall, this thesis demonstrates the feasibility of searching for disintegrating multiple systems with the method described, as well as the feasibility of identifying additional low-mass ejected components. Future Gaia data releases and upcoming large area near-infrared surveys and new space telescopes (e.g. LSST, EU- CLID, SPHEREX, NEOSurveyor) will enable me to search for even larger samples of disintegrating systems and more low-mass ejecta. This population will be fundamental to observationally constrain the rate at which this type of systems interact in the Galactic disk. The fundamental importance of searching for possible disintegrating multiple systems is its contribution in providing further constraints to the formation models of binaries and multiple systems and their evolution.