Tesis postgrado Astrofísica

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Examinando Tesis postgrado Astrofísica por Materia "ESTRELLAS DE BAJA MASA"

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    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).