Tesis postgrado Astrofísica
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Examinando Tesis postgrado Astrofísica por Materia "ESPECTROSCOPIA ASTRONOMICA"
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Ítem Dynamical stellar masses via high angular resolution techniques(Universidad de Valparaíso, 2021) Zúñiga Fernández, Sebastián; Oloffson, JohanMultiple 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).Ítem Searching for gas in debris disks(Universidad de Valparaíso, 2020-04) Iglesias Vallejo, Daniela; Bayo, Amelia (Supervisora); Olofsson, Johan (Supervisor); Wahhaj, Zahed (Supervisor)A debris disk is commonly described as a second generation circumstellar disk com- posed of dust grains, planetesimals and possibly already formed giant planets. It was long thought that debris disks were systems fully depleted of gas, but in the last few years the presence of gas has been detected in a increasing number of them. The na- ture of this gas is still under debate; it may be residual gas (leftover from earlier stages of the disk) or second generation gas (generated by the sublimation of exocomets or collisions of icy bodies), however, both possibilities would have great implications in the process of planet formation and evolution. An efficient way to search for this gas in debris disks is monitoring gas tracers using multi-epoch high-resolution UV-optical spectroscopy. A detection of gas in the line of sight of the star shows up as a very narrow absorption feature superposed to the photospheric absorption of lines such as Ca ii or Na i, which are very sensitive gas tracers. This Thesis is devoted to the search for gas via high-resolution spectroscopy in a sample of 301 debris disks with the pur- pose of estimating the frequency of gas in debris disks. We collected high-resolution UV-optical spectroscopic data from our own observations and the ESO archive for 273 objects, completing 91% of our sample. We analysed the multi-epoch spectra of each object searching for variable and stable non-photospheric absorption features of circumstellar origin. Firstly, we performed a detailed analysis of a sub-sample of 27 objects having multiple stable absorption features with the aim of determining whether their features were of circumstellar or interstellar origin. In this group we found two objects; c Aql and HR 4796, with variable absorption features attributable to the presence of star-grazing exocomets, and one object; HD 110058 with a stable circumstellar gas absorption. We concluded from these preliminary results that the presence of gas in debris disks might be a common phenomenon. Secondly, we studied the presence of unusually large non-photospheric absorption features found in several ionized lines of the object HD 37306, that lasted for several days. After analysing different possibilities we concluded that the most likely explanation might be an ex- ocometary break-up releasing a stream of gas that remained in orbit for at least a week around the star. Then, we analyzed the variability found in the Ca ii K lines of 97 objects with the purpose of distinguishing variable absorption features most likely produced by exocometary activity from variability of a different nature, like stellar pulsations, spots or radial velocity shifts, for instance. We found five candidates with variability consistent with exocometary activity: c Aql, 49 Cet, gam Tri, HR 4796 and HD 37306, two of them with no previous reports of exocomets besides this work. Finally, we studied a sub-sample of 107 objects presenting stable non-photospheric features in their Ca ii K lines within our updated database of observations in addi- tion to those in our first sub-sample of analysis. Similarly, the absorption features observed in these objects were analysed in order to determine whether they were of circumstellar or interstellar origin. We confirmed an interstellar origin for the features in 104 of these objects, one of them, 49 Cet having a blended feature of combined circumstellar and interstellar origin. In addition, we found three candidates with features of yet inconclusive origin that might be circumstellar but need further study to confirm it. Putting together our results, we found six debris disks with presence of circumstellar gas, five of them presenting variable absorption features attributable to exocometary activity and one of them with a stable circumstellar gas component. Considering that our sample is unbiased with respect to inclination, that the gas is more likely to be detected when the disk is observed close to edge-on, more easily detected in the spectra of early-type stars, the many detection challenges related to the sporadical nature of exocometary transits, and the interlopers of gas detection, then the evidence of circumstellar gas is significant. Taking into account the currently increasing number of detections, this imply the possibility that most debris disks may harbor some gas, challenging the current paradigm of debris disks.Ítem Strong gravitational lensing as a probe of structure from small to large scale(Universidad de Valparaíso, 2018-07) Rojas Olate, Karina; Motta, VerónicaThe gravitational lens effect occurs when the light is deflected by a gravitational field, generating multiple images or arcs. This powerful technique allows us to study structures at different scales in the universe that are usually related to different astrophysical problems. For instance, the characterization of dark objects in our galaxy (structure and mass distribution), the compact objects in the galaxy halos, the inner structure of quasars. Furthermore, it can be used to probe the cosmological model, for example through estimations of the Hubble constant (H0) and the mass distribution profile in galaxies, groups and cluster of galaxies. In this work I studied different structures that are affected or produced by grav- itational effect. In our galaxy at interstellar scale, I searched for microlensing effects in a region of the VISTA Variable in the V´ıa L´actea Survey (VVV). At galaxy-size scale, I studied the microlensing effect in lensed quasars to estimate the size (rs) and temperature profile (p) of their accretion disks and the effect of microlensing on time delay (∆t) measurements (related to H0). At cosmological scales, I performed a dynamical analysis for groups and clusters of galaxies to finally study the mass distribution profile in their halos. To reach these objectives I used visual and infrared images, spectroscopic data, models and simulations. The results presented in this thesis have been published in Rojas et al. (2014); Minniti et al. (2015); Verdugo et al. (2016); Motta et al. (2017); Courbin et al. (2018); Bonvin et al. (2018) among others, and part of the work is in preparation to be publish in Rojas et al. in prep(a,b), among others.