Detecting and characterizing planets around young stars (age up to some hundreds of Myr) are key aspects of exoplanet demographic studies, especially for understanding the mechanisms and timescales of planet formation and migration. However, detection using the radial velocity method alone can be very challenging. Young stars are exuberant like young guys, and they show their vivacity through high levels of magnetic activity. The amplitude of the signals in the radial velocities due to magnetic activity of such stars can be orders of magnitude larger than those induced even by massive planets.
An exemplary case is that of the ~2 Myr old star V830 Tau, around which an hot-Jupiter was detected in 2015 (orbital period ~5 days). Within the Italian large programme GAPS (Global Architecture of Planetary Systems), we observed V830 Tau with the HARPS-N spectrograph for 2.5 years, with the goal of independently confirm and characterize the planet using a different dataset of radial velocities. Despite the high quality of the HARPS-N data and the diversity of tests we performed, we could not detect the planet V830 Tau b. Even though we cannot rule out the existence of V830 Tau b with very high confidence, nonetheless our results cast several doubts, with implications on the assessment of the occurrence rate of young planets, and on their formation mechanisms and migration pathways.
This study is described in a paper lead by Mario Damasso (INAF-OATo) and accepted for publication on Astronomy & Astrophysics. The pre-print is available at the following link http://arxiv.org/abs/2008.09445