Kinematic structure and age of a Scorpius--Centaurus subcomponent: implications for PDS 70 planetary system
Abstract
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±1.0~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 ∼5.5 compared to \textit{Gaia}. %We supplement these measurements with Hα and lithium equivalent widths as youth diagnostics. We combine these with \textit{Gaia} DR3 astrometry in the \texttt{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 ≈ 12--$16$~Myr for PDS 70, ruling out ages as young as the published isochronal estimate. At this kinematic age, PDS~70~\textit{b}'s (and to a lesser extent, PDS~70~\textit{c}'s) luminosity is incompatible with warm-start cooling tracks under current dynamical mass constraints. The most natural interpretation is that PDS~70~\textit{b} formed ≈10.5 Myr after its host star, and no less than ≈7.7 Myr after it.
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BibTeX
@misc{arunima2026kinematic,
title = {{Kinematic structure and age of a Scorpius--Centaurus subcomponent: implications for PDS 70 planetary system}},
author = {Arunima Arunima and Mike Ireland and Mark Krumholz},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.25987},
eprint = {2610.25987},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.25987},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Kinematic structure and age of a Scorpius--Centaurus subcomponent: implications for PDS 70 planetary system
AU - Arunima Arunima
AU - Mike Ireland
AU - Mark Krumholz
PY - 2026
DA - 2026/10/19
PB - arXiv
DO - 10.48550/arxiv.2610.25987
UR - https://arxiv.org/abs/2610.25987
AB - 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±1.0~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 ∼5.5 compared to \textit{Gaia}. %We supplement these measurements with Hα and lithium equivalent widths as youth diagnostics. We combine these with \textit{Gaia} DR3 astrometry in the \texttt{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 ≈ 12--$16$~Myr for PDS 70, ruling out ages as young as the published isochronal estimate. At this kinematic age, PDS~70~\textit{b}'s (and to a lesser extent, PDS~70~\textit{c}'s) luminosity is incompatible with warm-start cooling tracks under current dynamical mass constraints. The most natural interpretation is that PDS~70~\textit{b} formed ≈10.5 Myr after its host star, and no less than ≈7.7 Myr after it.
ER -