BASE-9 Isochrone Fits Deliver Sub-Gyr Ages for 146 HZ-Host Stars, Highlighting Evolved Targets

The work tracks outward HZ migration along MESA evolutionary tracks to compute continuous residence times, showing that some present-day HZ planets spent earlier epochs interior to the inner edge. This directly informs which worlds experienced sustained liquid-water conditions versus brief or intermittent ones. Sample selection deliberately favors evolved stars where isochrones separate most strongly, yielding median age uncertainties below 0.5 Gyr for subgiants versus 2–4 Gyr for lower-main-sequence hosts.

Prior age-dating efforts relied on activity or gyrochronology, both of which degrade for stars older than ~2 Gyr or lacking rapid rotation. The new catalog therefore supplies the first uniform, photometry-plus-parallax age scale for a statistically useful HZ sample. Cross-checks against asteroseismic ages for overlapping Kepler hosts confirm the BASE-9 posteriors are unbiased at the 10–15 % level.

The immediate payoff is target prioritization: subgiant hosts with <0.3 Gyr age precision and multi-Gyr HZ residence times become prime candidates for JWST or ELT atmospheric spectroscopy. The catalog also flags systems whose HZ planets may have lost atmospheres during early high-luminosity phases, refining interpretations of non-detections.

Next steps include incorporating TESS rotation periods and Gaia DR4 spectrophotometry to shrink uncertainties for the still-dominant main-sequence cohort, plus coupling the ages to climate models that include evolving stellar spectra.