Tesis postgrado Astrofísica

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Examinando Tesis postgrado Astrofísica por Materia "ASTROMETRIA"

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  • Miniatura
    Ítem
    Dynamical stellar masses via high angular resolution techniques
    (Universidad de Valparaíso, 2021) Zúñiga Fernández, Sebastián; Oloffson, Johan
    Multiple stellar systems are abundant in our galaxy. Almost half of solar-like field stars have at least one companion. Multiple systems are the perfect playground to de- termine the stellar mass, which the one of the most fundamental parameter in stellar astrophysics, without having to rely heavily on models. In this thesis we present the results of detection and orbital characterisation of multiple systems in Young (∼ 5 − 100 Myr) associations. The aim is to identify binary and multiple systems in our sample and determine their dynamical masses. Ultimately, the results of this work should provide valuable information to calibrate evolutionary models of low- mass (< 0.5 M8) pre-main sequence stars. The SACY sample (Search for Association Containing Young stars) is a collection of nearby (< 200 pc) young (∼ 5 − 100 Myr) stars, mostly with estimated masses ∼ 0.1 − 1.2 M8. The sample is structured in groups consistent of separated populations known as moving group or associations, such as the β−Pic moving group and the AB Doradus association. In Chapter 2, we identify 68 spectroscopic binaries (SBs) among our sample of 410 objects and update the SB fraction of each young association. Our results hint at the possibility that the youngest associations have a higher SB fraction (∼ 30%) in com- parison with the five oldest (∼ 10%). This difference suggests could hint towards a non-universal primordial multiplicity in the youngest associations. One of the well known SB in our sample is the quadruple system HD 98800. The system is composed of two SBs orbiting each other (AaAb and BaBb), with a gas-rich disc in polar configu- ration around BaBb. We obtain new astrometric measurements using long-baseline in- frared interferometric observations with the VLTI/PIONIER instrument. Combining our new astrometry with archival observations and radial velocity measurements, we determine the orbital parameters of both subsystems. We refine the orbital solution of BaBb and derive, for the first time, the orbital solution of AaAb. In addition, we con- firm the polar configuration of the disc around BaBb. Furthermore, we present some preliminary results on astrometric measurements for seven interesting binary systems that we are monitoring with AO-imaging observations. Additionally, we also report new estimates on the astrometry of seven binaries using VLTI PIONIER observations. These astrometric measurements will be used to prepare the future work towards full orbital characterisation and dynamical masses determination in those multiple sys- tems. Finally, in Chapter 5 we describe our contribution to the commissioning of the New Adaptive Optics Module for Interferometry (NAOMI).
  • 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.