DMPP-3: confirmation of short-period S-type planet(s) in a compact eccentric binary star system, and warnings about long-period RV planet detections

Abstract We present additional HARPS radial velocity observations of the highly eccentric (e ∼ 0.6) binary system DMPP-3AB, which comprises a K0V primary and low-mass companion at hydrogen burning limit. The has 507 d orbital period 1.2 au semi-major axis. component harbours known 2.2 M⊕ planet, DMPP-3A b, with 6.67 day orbit. New measurements constrain periastron passage for orbit add further integrity to previously derived solutions both planet orbits. Gaia astrometry independently confirms orbit, establishes inclination is 63.89 ± 0.78○. performed dynamical simulations establish that identified ∼800 RV signal cannot be attributed an orbiting body. observations, deviation from strict periodicity, our new analyses activity indicators suggest caused by stellar activity. conclude there may long “detections” in other systems are similar misinterpreted artefacts. Without unusual planet-hosting star we could have accepted as probable planet. Further monitoring DMPP-3 will reveal signatures can used most efficiently identify these imposters. also report threshold detection (0.2 per cent FAP) ∼2.26 periodicity RVs, potentially Earth-mass S-type interior b.