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dc.contributor.advisorScholz, Alexander
dc.contributor.authorRigon, Laura
dc.description.abstractStars form from the collapse of molecular clouds and evolve in an environment rich in gas and dust before becoming Main Sequence stars. During this phase, characterised by the presence of a protoplanetary disc, stars manifest changes in the structure and luminosity. This thesis performs a multi-wavelength analysis, from optical to mm range, on a sample of young stars (YSOs), mainly Classical T Tauri (CTTS). The purpose is to study optical and infrared variability and its relation with the protoplanetary disc. Longer wavelength, in the mm range, are used instead to investigate the evolution of the disc, in terms of dust growth. In optical, an F-test on a sample of 39 CTTS reveals that 67\% of the stars are variable. The variability, quantified through pooled sigma, is visible both in magnitude amplitudes and changes over time. Time series analysis applied on the more variable stars finds the presence of quasi periodicity, with periods longer than two weeks, interpreted either as eclipsing material in the disc happening on a non-regular basis, or as a consequence of star-disc interaction via magnetic field lines. The variability of YSOs is confirmed also in infrared, even if with lower amplitude. No strong correlations are found between optical and infrared variability, which implies a different cause or a time shift in the two events. By using a toy model to explore their origin, I find that infrared variations are likely to stem from emissions in the inner disc. The evolution of discs in terms of dust growth is confirmed in most discs by the analysis of the slope of the spectral energy distribution (SED), after correcting for wind emission and optical depth effects. However, the comparison with a radiative transfer model highlights that a number of disc parameters, in particular disc masses and temperature, dust size distribution and composition, can also affect the slope of the SED.en_US
dc.description.sponsorshipFunded by the European Union Seventh Framework Programme FP7-2011 under grant agreement no 284405en
dc.description.sponsorshipFunded by the European Union Seventh Framework Programme FP7-2011 under grant agreement no 284405en
dc.publisherUniversity of St Andrews
dc.rightsAttribution-NonCommercial-NoDerivatives 4.0 International*
dc.subjectStar evolutionen_US
dc.subjectPlanet formationen_US
dc.subjectProtoplanetary discsen_US
dc.subjectCircumstellar matteren_US
dc.subjectT Tauri starsen_US
dc.subjectOptical variabilityen_US
dc.subjectInfrared variabilityen_US
dc.subjectTime series analysisen_US
dc.subjectLong term periodicityen_US
dc.subjectDust growthen_US
dc.subjectDust opacity indexen_US
dc.subjectMillimeter slopeen_US
dc.subjectDelta correctionen_US
dc.subject.lcshEarly starsen_US
dc.subject.lcshProtoplanetary disksen_US
dc.titleLights and shadows : multi-wavelength analysis of young stellar objects and their protoplanetary discsen_US
dc.contributor.sponsorSeventh Framework Programme (European Commission)en
dc.type.qualificationnamePhD Doctor of Philosophyen_US
dc.publisher.institutionThe University of St Andrewsen_US
dc.publisher.departmentSchool of Physics&Astronomyen_US

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    Except where otherwise noted within the work, this item's licence for re-use is described as Attribution-NonCommercial-NoDerivatives 4.0 International