Differential Rotation in Sun-like Stars from Surface by Martin Bo Nielsen

By Martin Bo Nielsen

In his PhD dissertation Martin Bo Nielsen plays observational experiences of rotation in stars just like the sunlight. the internal rotation in stars is assumed to be one of many riding mechanisms of stellar magnetic task, yet previously this mechanism used to be unconstrained via observational data.
NASA’s Kepler area undertaking offers high-precision observations of Sun-like stars which enable rotation to be inferred utilizing self sustaining tools: asteroseismology measures the rotation of the stellar inside, whereas the brightness variability attributable to gains at the stellar floor hint the rotation of its outermost layers. by way of combining those strategies Martin Bo Nielsen was once in a position to position top limits at the version of rotation with intensity in 5 Sun-like stars. those effects recommend that the internal of alternative Sun-like stars additionally rotate in a lot an analogous method as our personal Sun.

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Extra info for Differential Rotation in Sun-like Stars from Surface Variability and Asteroseismology

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The choice of algorithm is often motivated by the computation time of ln L, as it may be necessary to explore a large section of parameter space and thus evaluate the likelihood many times. The aim is to find the global maximum in as few steps as possible. Such methods include the down-hill simplex method (Nelder and Mead 1965), gradient ascent/descent method, Powell’s method (Powell 1964) and many more. However, such algorithms suffer from the possibility of getting stuck in a local maximum. Alternatively one can randomly or pseudo-randomly sample the parameter space.

This was interpreted as the presence of two different dynamos operating in the two groups of stars as also suggested by Vaughan and Preston (1980) and Durney et al. (1981). Detailed inversions of the surface magnetic field structure with spectropolarimetry have also shown different behaviors of the magnetic dynamos of other stars, from non-cyclic behavior (Jeffers et al. 2011; Donati et al. 2003) to the same field reversal behavior as the Sun (Donati et al. 2008; Fares et al. 2009). These studies all measure the physical effects of stellar dynamos which are manifested at the surface.

4) where /π is equivalent to the rotational splitting which is often denoted by δν. In most studies this is what is used when fitting oscillation spectra in order to measure the mean rotation of stars (Bazot et al. 2007; Appourchaux et al. 2008; Gizon et al. 2013; Lund et al. 2014a; Davies et al. 2015). 8 In the limit of averaging over an infinite number of noise realizations, the peaks in the power spectrum tend toward Lorentzian profiles (Anderson et al. 1990). This is typically known as the limit spectrum.

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