Kinematic structure and age of a Scorpius--Centaurus subcomponent: implications for PDS 70 planetary system

PDS 70, the only system with two directly imaged protoplanets embedded in their natal disk, is a benchmark for giant-planet formation theory. Interpreting the planetary luminosities requires a precise age for the host star, but the widely adopted isochronal age of 5.4 plus or minus1.0 Myr is substantially younger than ages inferred for the Upper Centaurus--Lupus (UCL) population with which it is associated. We address this discrepancy by determining a new kinematic age for PDS 70 using radial velocities for 405 candidate members of the Scorpius--Centaurus T subcomponent from the Wide Field Spectrograph (WiFeS) on the ANU 2.3 m telescope, reducing uncertainties by a factor of about5.5 compared to Gaia. %We supplement these measurements with H α and lithium equivalent widths as youth diagnostics. We combine these with Gaia DR3 astrometry in the Chronostar kinematic reconstruction framework to derive a posterior-weighted kinematic age of approximately 10 -- 15 Myr for all the T subcomponent stars, with a kinematic age of about 12 -- 16 Myr for PDS 70, ruling out ages as young as the published isochronal estimate. At this kinematic age, PDS 70 b's (and to a lesser extent, PDS 70 c's) luminosity is incompatible with warm-start cooling tracks under current dynamical mass constraints. The most natural interpretation is that PDS 70 b formed about10.5 Myr after its host star, and no less than about7.7 Myr after it.