The magnetic activity, winds and planets of young, cool stars

The magnetic activity, winds and planets of young, cool stars

This thesis uses spectropolarimetry to observationally investigate the properties of dynamos and winds of young cool stars, and search for young planets. The techniques of Doppler Imaging and Zeeman Doppler Imaging were used to reconstruct the surface brightness and large-scale magnetic field morphologies of four low-mass weak-line T Tauri stars. The first sample consists of two solar mass stars of different ages, V1095 Sco (1 Myrs) and TWA 9A (10 Myrs). The second sample analysed consists of two 10 Myr old, M-type stars, TWA 25 (0.7 M⊙) and TWA 7 (0.4 M⊙). Taken together, the reconstructed brightness maps of these young cool stars show a wide variety in their morphologies, as do the reconstructed large-scale magnetic fields. These findings are in agreement with the results of the wider Magnetic Topologies of Young Stars and the Survival of close-in giant Exoplanets (MaTYSSE) large programme, of which this thesis is a part. The variations in radial velocity are examined for all four stars, using the brightness information where available to filter out activity jitter, improving the detection limits for close-in giant planets around these stars.

In addition to this investigation of pre-main sequence stellar dynamos and young planetary systems, a time series of magnetic field observations of the planet-hosting young star T Boötis spanning more than half a decade - the longest to date - is used to infer changes in the stellar wind, and the resulting potential impacts on the orbiting
planet.

In overall terms, this thesis demonstrates that spectropolarimetry is a valuable tool for understanding the magnetic dynamos of young cool stars, modelling stellar winds, and for searching for planets in the presence of stellar activity. In future, spectropolarimetry used as part of radial velocity surveys can advance our understanding of the early evolution of cool stars and their planetary systems.