We present a new precision radial velocity ( RV ) dataset that reveals multiple planets orbiting the stars in the \sim 360 AU , G2 + G2 “ twin ” binary HD 133131AB .
Our 6 years of high-resolution echelle observations from MIKE and 5 years from PFS on the Magellan telescopes indicate the presence of two eccentric planets around HD 133131A with minimum masses of 1.43 \pm 0.03 and 0.63 \pm 0.15 \mathcal { M } _ { J } at 1.44 \pm 0.005 and 4.79 \pm 0.92 AU , respectively .
Additional PFS observations of HD 133131B spanning 5 years indicate the presence of one eccentric planet of minimum mass 2.50 \pm 0.05 \mathcal { M } _ { J } at 6.40 \pm 0.59 AU , making it one of the longest period planets detected with RV to date .
These planets are the first to be reported primarily based on data taken with PFS on Magellan , demonstrating the instrument ’ s precision and the advantage of long-baseline RV observations .
We perform a differential analysis between the Sun and each star , and between the stars themselves , to derive stellar parameters and measure a suite of 21 abundances across a wide range of condensation temperatures .
The host stars are old ( likely \sim 9.5 Gyr ) and metal-poor ( [ Fe/H ] \sim -0.30 ) , and we detect a \sim 0.03 dex depletion in refractory elements in HD 133131A versus B ( with standard errors \sim 0.017 ) .
This detection and analysis adds to a small but growing sample of binary “ twin ” exoplanet host stars with precise abundances measured , and represents the most metal-poor and likely oldest in that sample .
Overall , the planets around HD 133131A and B fall in an unexpected regime in planet mass-host star metallicity space and will serve as an important benchmark for the study of long period giant planets .