Abstract: The Beta Pictoris system is unique: It is a young (20Ma), very bright star, with a debris disk seen edge-on, and a directly imaged planet, Beta Pic b. In addition, the planet, which has a probable 18 years orbital period, is due to nearly transit in front of its star during 2017. In 1981 a mysterious event has been invoked as possibly due to the same planet transiting the star. The unique opportunity of this configuration led an international consortium to follow the star photometrically and by radial velocimetry. I will present the observations conducted from the Concordia base, Antarctica with the ASTEP photometric telescope continuously from March to October 2017. The lightcurves of excellent quality allow a clear determination of the pulsation frequencies of the star (a Delta Scuti) and the possibility to detect signs of Beta Pic b or its perturbations of the disk, possible rings or large moons, and additional planets. At the time of the presentation, the observations will have just ended, enabling a complete analysis.

Abstract: High southern latitude regions present specificities that are highly relevant for studying the climate in connection with the atmospheric chemistry. Contrary to regions of the rest of the world, Antarctica is still considered as a pristine environment not yet influenced by predominant anthropogenic emissions (with the notable exceptions of GHG) and thus represents the last continental-size natural laboratory. Polar snow-air-radiation interactions and the specific oxidant character of the polar atmosphere are key in order to decipher the right information buried in the ice and the current chemical stability of the polar atmosphere. Previous Antarctic campaigns have shown atmospheric similarities between the Antarctic Plateau (at Dome C, Concordia) and other regions. However, several differences are yet to be explained: the large NO2:NO ratios previously found in ambient air indicates the existence of an unknown source of NO2 above the Antarctic Plateau. These observations question either the reliability of previous measurements or the lack of our understanding of the NOx chemistry. Novel optical instruments based on the incoherent broadband cavity enhanced absorption spectroscopy technique (IBBCEAS) were developed. The instruments can measure simultaneously NO2, NOx and NO with detection limits of 11, 10 and 21 ppt, respectively (1σ) within 22 minutes of measurements. The two compact and transportable instruments were deployed during the 2019/20 Dome C summer campaign. Atmospheric measurements together with flux chamber experiments were performed for determining the snowpack NOx emissions and the NO2:NO ratio. The observations seem to differ from the conclusions of the previous Antarctic campaigns. Assuming steady state and maximum radiations, the theoretical NO2:NO ratio from the period observed in December was calculated to be 0.38 ± 0.15 and 0.31 ± 0.12 in January. The instruments measured a ratio close to steady state in December (0.25 ± 0.25) while the ratio observed in January (1.248 ± 0.792) indicates the presence of a strong NO oxidant or an unknown source of NO2. Flux chamber experiments on different types of snow were done during this campaign, and the results will help deepen our knowledge of Antarctic atmospheric chemistry.