ESPRESSO's RVs down to the 10cm/s level

The RVs were derived both with the cross-correlation method and template matching, as well as over the blue and red ESPRESSO detectors independently to identify colour-dependent parasitic effects that were of an instrumental or a stellar nature. The study of RVs was complemented by an investigation of stellar activity indicators variation using photospheric information and chromospheric indexes. A simple model of stellar pulsations successfully reproduced the intra-night RV scatter of HD10700 down to a few cm/s.

For HD102365 and HD20794 an additional source of scatter at the level of several 10cm/s is required to explain the data. A kima analysis was used to evaluate the number of planets supported by the nightly averaged time series of each of these three stars, under the assumption that a quasi-periodic Gaussian process (GP) regression is able to model the activity signal. While a frequency analysis of HD10700 RVs identifies a periodic signal at 20d, when it is modelled along with the activity signal the signal is formally non-significant.

Moreover, its physical origin remains uncertain due to the similarity with the first harmonic of the stellar rotation. ESPRESSO data on their own do not provide conclusive evidence to support the existence for planets around HD10700, HD102365 or HD304636. In addition, the comparison of RVs with the contemporaneous indicators display a strong correlation for HD102365.

The direct interpretation is that half of the RV variance on this star is directly attributed to activity. ESPRESSO is shown to reach an on-sky RV precision of better than 10cm/s on short timescales (<1h) and of 40cm/s over 3.5yr. A subdivision of the datasets showcases a precision reaching 20-30cm/s over one year.

These results provide stringent constraints on the impact of granulation mechanisms on RV. In spite of no detections, our analysis of HD10700 RVs demonstrates a sensitivity to planets with a mass of 1.7M_{Earth}_ for periods of up to 100d, and with a mass of 2-5M_{Earth}_ for the star's HZ.