Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685058
Title: Lights and shadows : multi-wavelength analysis of young stellar objects and their protoplanetary discs
Author: Rigon, Laura
ISNI:       0000 0004 5923 8355
Awarding Body: University of St Andrews
Current Institution: University of St Andrews
Date of Award: 2016
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Abstract:
Stars 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.
Supervisor: Scholz, Alexander Sponsor: European Union Seventh Framework Programme FP7-2011
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.685058  DOI: Not available
Keywords: Star evolution ; Planet formation ; Protoplanetary discs ; Circumstellar matter ; T Tauri stars ; Optical variability ; Infrared variability ; Time series analysis ; Long term periodicity ; Dust growth ; Dust opacity index ; Millimeter slope ; Delta correction ; QB843.E2R5 ; Early stars ; Protoplanetary disks ; Stars--Evolution
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