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Title: A pathway to earth-like worlds : overcoming astrophysical noise
Author: Cegla, Heather Marie
ISNI:       0000 0004 5369 6144
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2014
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Astrophysical noise poses a severe stumbling block on the pathway to the radial velocity confirmation of habitable Earth-like worlds. In particular, photospheric magneto-convection sets a fundamental limitation on the obtainable radial velocity precision. Consequently, in this thesis, I develop a multi-component parameterisation of granulation that can be used to reconstruct stellar line asymmetries and radial velocity shifts due to photospheric convective motions across the stellar disc. The parameterisation consists of four components: granules, magnetic and non-magnetic intergranular lanes, and magnetic bright points. These components are constructed by averaging Fe I 6302 A line profiles output from detailed radiative transport calculations of the solar photosphere. Each of the four categories adopted are based on magnetic field and continuum intensity limits determined from examining three dimensional magnetohydrodynamic simulations with an average magnetic flux of 200 G. I demonstrate that, on average, these four components can accurately reconstruct granulation produced from modelling 12 x 12 Mm2 areas on the solar surface, to better than ~ ± 20 cm s-'. I also establish the applicability of this parameterisation across magnetic stellar activity levels by 'successfully reconstructing profiles from a 50 G simulation. This parameterisation is then used to construct Sun-as-a-star observations to identify how the convective plasma motions on the stellar surface alter the disc-integrated profiles. I find that the velocity asymmetry (a measurement comparing the spectral information content of the blue wing to the red wing) and brightness measurements are the best-suited diagnostics for reducing granulation noise to a level sufficient for the confirmation of habitable, terrestrial-mass planets. In addition, I identify a potential new source of astrophysical noise, and establish tentative links between photometric variability and radial velocity variations in quiet stars; both of which are important steps on the pathway to Earth-like alien worlds.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available