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The effect of stellar magnetic activity on protoplanetary discs and exoplanet detection

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Worlds beyond our solar system

Astronomers have located hundreds of planets outside of the solar system. EU-funded researchers studied how stellar activity shapes the environment of these exoplanets, giving rise to a new perspective about magnetic phenomena.

Climate Change and Environment

The "jitter" arising from the star's magnetic activity is very similar in amplitude to signals caused by orbiting low-mass planets. Disentangling these signals is the biggest challenge in the detection of exoplanets based on the radial velocity profiles. Researchers working on 'The effect of stellar magnetic activity on protoplanetary discs and exoplanet detection' (ACTIVITY & PLANETS) project focused on the magnetically active regions such as dark spots on the stellar surface. The Sun's activity is well known and therefore was selected by project scientists to estimate the velocity variations produced by spots drifting across the face of the Sun. Their investigations were then extended to similar stars, which are of interest in the quest for an Earth-like planet. Specifically, the jitter in radial velocity measurements was estimated from the continuum light curve of the Sun based on distortions of emission lines caused by spots. Solar observations were used by the project team as the starting point. Photometric proxies were then identified which make it possible to remove stellar activity contribution from exoplanet velocity profiles. A combination of observations in mid-infrared and sub-millimetre wavelengths was used to study the effects of stellar magnetic activity on the first stages of planets' formation. Newly formed stars in the Orion nebula cluster which were surrounded by a swirling disc of dust and gas were selected. ACTIVITY & PLANETS scientists looked for the effects of X-ray emissions on disc chemistry. It is well established that the tiny solids in the disc coalesce to create rocky 'planetesimals' that collide and grow to eventually form planets. However, the ACTIVITY & PLANETS scientists' findings suggest that the disc influenced by X-ray emissions is following a slightly different route to making planets. This work will allow astronomers to re-evaluate the magnetic activity on the surface of stars, providing more insight into the planet-building process.

Keywords

Planets, solar system, stellar activity, exoplanets, magnetic, jitter, radial velocity, photometric, Orion nebula, X-ray emissions

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Climate Change and Environment

2 April 2014