Correcting Astrophysical Noise in HARPS-N RV Measurements

Radial velocity instrumental precision has improved to the degree that measurements are now limited in part by the noise intrinsic to the host star, or stellar 'jitter'. Several different phenomena contribute to the observed jitter, including pressure waves, granulation, magnetic features caused by stellar activity, and solar-like magnetic cycles. The amplitude of these effects ranges from 10 to 400 cm/s, depending on stellar type, and pose a significant limitation to detecting Earth analogues. We carry out a survey of bright, quiet stars with the new HARPS-N instrument, an ultra-stabilized R=115,000 cross-dispersed spectrograph located on the 3.6m Telescopio Nazionale Galileo on the island of La Palma. We look for correlations between these radial velocity measurements and known activity indicators, including line bisector measurements and the CaII index. We will correct for the presence of starspots by locating and removing quasi-periodic signals consistent with stellar rotation rate. We also investigate new correlations between radial velocity measurements and other observables, including variations in line depth ratios. By correcting for these combined effects, we can improve the radial velocity precision, enabling the detection of low-mass planets.