Vol. 575
In section 10. Planets and planetary systems

The GAPS programme with HARPS-N at TNG .V. A comprehensive analysis of the XO-2 stellar and planetary systems

The XO-2 system is peculiar and extremely interesting. It is a binary star with two solar-like components, XO-2N and XO-2S, each one possessing a system of giant planets. XO-2N has one giant planet of 0.6 times the mass of Jupiter in a 2.6-day orbit that was discovered in transit in 2007. XO-2S has two giant planets that were discovered by the radial-velocimetry technique: planet b has 0.26 Mjup for a 18-day orbital period, while planet c has 1.4 Mjup for a 121-day orbital period. Damasso et al. observed the two components both in radial velocimetry and photometry. They find that XO-2N seems to be spinning faster than XO-2S, which could be a consequence of a tidal spin-up of XO-2N by its planet. Even more intriguing, they find that the abundance of iron in XO-2N is 0.054 dex greater than in XO-2S. Given that the two stars were born from the same molecular cloud core, this difference in abundance seems to confirm that the formation of planets affects the stellar compositions.