An upcoming ambitious objective of science is to determine the frequency and the conditions for the emergence of life. After the discovery of more than 800 exoplanets in fifteen years, mostly giant planets, the next step is the detection of terrestrial planets in the habitable zone of their stars, and the determination of their properties. With a current accuracy below 1m/s (eg HARPS at 3.6m telescope, La Silla Observatory, ESO) technical leads to improve this accuracy and projects of high-precision spectrographs (eg 10cm/s ESPRESSO at VLTs, ESO), Doppler spectroscopy is expected to detect and give the mass of the terrestrial planet population. When, in addition, these planets are also in transit, we can measure their radius and have access to their average density, and thus probe their internal structure.
However, the radial velocity (RV) technique, as transits, are indirect detection. Stellar activity, such as non-radial pulsations, granulation or magnetism affect the measurements, moreover when planets have terrestrial masses. These stellar phenomena may hamper the detection of these small planets, but also could cause false detections if the stellar signal is periodically stable. Specifically, the magnetic activity, which results in the presence and variability of dark and bright spots at the surface of the star, is the most limiting factor in RV. The resulting RV amplitudes can be one order of magnitude larger than those due to an Earth-like planet in the habitable zone of its star. In addition, stellar activity has also an impact in photometry, distorting and changing the transit depth, which prevents a correct and accurate measurement of the planetary radius. Understand and correctly model the stellar activity is of paramount importance in order to explore the population of exoplanets similar to Earth and determine their properties.
Portuguese Node: CAUP
Co-PI: Alexandre Santerne
French Node: Laboratoire d'Astrophysique de Marseille
1 January 2014
31 March 2016
Fundação para a Ciência e a Tecnologia