HD 176986 HARPS Rvs and activity indicators

We utilize historical and recently collected RV measurements to investigate the presence of Earth- and super-Earth-like planets in the habitable zone of HD 176986. We monitored the system with HARPS and HARPS-N. We joined historical datasets with new data collected in an ongoing blind search program. We took advantage of recently developed tools for RV extraction and stellar activity filtering.

The analysis of activity indicators permits us to determine the period of the magnetic cycle of the star alongside its rotation period. We performed a joint analysis of RVs and activity indicators through multidimensional GPs to better constrain the activity model in RVs and avoid overfitting. We detected a new planet orbiting the star and retrieved the two known planets.

HD 176986 b has an orbital period of 6.49164_-0.00029_^+0.00030^d and a minimum mass of 5.36+/-0.44M_{Earth}_. HD 176986 c has an orbital period of Pc=16.8124+/-0.0015d and a minimum mass of 9.75_-0.64_^+0.65^M_{Earth}_. HD 176986 d has an orbital period of 61.376_-0.049^+0.051^d and a minimum mass of 6.76_-0.92_^+0.91^M_{Earth}_.

From the analysis of activity indicators, we find evidence of a magnetic cycle with a period of 2432_-59_^+64^d, along with a rotation period of 36.05_-0.71_^+0.67^d. We discover a new planet in the multi-planet system orbiting the K-type star HD 176986. All the planets have minimum masses compatible with super-Earths or mini-Neptunes.