The HAges Catalog: Stellar Ages for High Priority HWO Target Stars

Abstract: Precise stellar ages (uncertainties $\lesssim 1$ Gyr, or $\sim 20\%$ at solar age) are required to discern evolutionary trends in atmospheric biosignatures of terrestrial habitable zone exoplanets surveyed by the Habitable Worlds Observatory (HWO) and will aid in constraining planetary interior evolution and target prioritization. We present a catalog of stellar ages for Tier 1 and Tier 2 targets in the HWO Target Stars and Systems (TSS) sub-working group's TSS25 list, compiling published literature ages derived from high-precision methods. The sample comprises 659 stars likely to be observed by HWO, independent of the final mission architecture. This initial catalog focuses on asteroseismology and gyrochronology, which can achieve $\sim 20\%$ precision for the majority of these stars. We find that only $\sim 5\%$ of the sample have asteroseismic ages and $\sim 20\%$ have gyrochronal ages, with just $\sim 2\%$ having constraints from both methods. For stars with multiple published measurements, the median reported statistical uncertainties are slightly smaller than the systematic uncertainties: $\sim 9\%$ versus $\sim 12\%$ for asteroseismology and $\sim 16\%$ versus $\sim 18\%$ for gyrochronology. The scarcity of precise stellar ages in this sample highlights the need for a concerted effort to obtain robust age constraints in advance of HWO; this catalog is intended as a living resource that will be regularly updated in the lead-up to the mission.

• The paper compiles 490 published age measurements from 99 sources for 127 of 659 high-priority HWO target stars, documenting methods, inputs, and uncertainties in a public catalog.
• Asteroseismic and gyrochronological age estimates show median inter-publication scatters of 12.3% and 18.3%, respectively, indicating that reported statistical errors often understate total uncertainty.
• The paper finds that gyrochronology underestimates ages by about 47% for stars older than 6 Gyr and identifies TESS, PLATO, gyro-kinematics, and chemical clocks as routes to improve coverage.

Motivation and scientific context

Stellar ages with uncertainties of order 1 Gyr, or roughly 20% at solar age, are a prerequisite for interpreting the atmospheric biosignatures that the Habitable Worlds Observatory (HWO) is expected to measure on terrestrial habitable zone planets. Age constraints inform both the prioritization of systems likely to retain habitable conditions and the interpretation of evolutionary trends in detected biosignatures, as well as models of planetary mantle degassing lifetimes. The paper by Ware, Ruppert, and Young addresses this need directly by compiling published ages for the highest-priority HWO targets into a publicly available resource, the HAges Catalog (2605.12647).

The target sample derives from the TSS25 list produced by the HWO Target Stars and Systems (TSS) sub-working group, which itself builds on the Habitable Worlds Observatory Preliminary Input Catalog (HPIC) of roughly 13,000 nearby (< 50 pc), bright ($T$ and $G < 12$) stars. Tier 1 comprises the 164 targets in the ExEP Mission Star List, selected on the basis of habitable zone accessibility for a 6-m-class direct imaging mission; Tier 2 adds 495 targets identified through exo-Earth yield simulations with AYO and EXOSIMS as having high probability of observation regardless of final architecture. The catalog adopts the combined 659 Tier 1 and Tier 2 stars.

Scope of age-dating methods

The initial release restricts itself to two methods capable of approximately 20% precision for FGK-type dwarfs and subgiants, which dominate the sample. Asteroseismology infers interior structure from solar-like oscillations; statistical precisions below 20% are common for well-characterized solar-like oscillators, with sub-10% achievable for the best cases. Its dominant limitation is systematic: ages depend on stellar evolution and oscillation models plus seismic scaling relations, so systematics can match or exceed statistical errors. For the Kepler LEGACY sample, median statistical and systematic age uncertainties are about 8% and 12%, respectively. Gyrochronology exploits magnetic braking to map rotation period to age, with typical statistical uncertainties of 10–40%. It inherits systematics from cluster age calibrations, assumes rotation converges onto a unique age sequence (violated by young stars' intrinsic spread), and is generally limited to ages below roughly 4 Gyr because older stars exhibit weakened magnetic braking and a flattened age-rotation relation. Gyro-kinematic relations calibrated against vertical velocity dispersion offer a route to older ages, up to approximately 14 Gyr.

Catalog construction

Because asteroseismic ages are typically reported for individual stars rather than large samples, the compilation required manual literature searches via ADS using SIMBAD identifiers, supplemented by direct author contact where multiple pipelines or model results were discussed but not individually reported. For gyrochronology, the authors required ages derived from measured rotation periods obtained through periodogram analysis, excluding estimates based on $R'_{\rm HK}$ or $v\sin i$, and required traceability of each rotation period to its original source. Two deliberate exclusions are documented: the asteroseismic age of $\gamma$ Pav from Mosser et al. (2008), invalidated by an incorrect even/odd mode identification, and gyrochronal ages for 51 Peg based on a spurious 37-day rotation period later revised to 21.9 days.

The catalog records all individual published measurements rather than adopted values, along with masses, evolution and oscillation codes, rotation periods, and the age-rotation relations used. Duplicate gyrochronology entries arising from identical inputs to the Barnes (2007) and Mamajek & Hillenbrand (2008) relations were removed in favor of the earlier publication, though "near duplicates" with slightly different inputs were retained — a choice the authors test explicitly (see below).

Current contents and coverage

The catalog draws on 99 literature sources containing 490 individual ages for 127 unique stars:

Method	Ages	Unique stars	Fraction of sample	Median ages per star
Asteroseismology	164	31	~5%	5
Gyrochronology	326	110	~17%	3

Only 14 stars (~2%) have ages from both methods. This scarcity is the central empirical finding: more than 80% of the most likely HWO targets lack precise ages from either method, which the authors argue motivates a concerted community effort over the coming decade(s).

For stars with multiple published measurements, the scatter between independent determinations serves as an empirical proxy for systematic uncertainty. The median standard deviation between published ages is below 1 Gyr for both methods — 0.64 Gyr for asteroseismology and 0.4 Gyr for gyrochronology — though the latter figure partly reflects the younger median age of the gyrochronology sample (2.09 Gyr versus 5.69 Gyr). Expressed in fractional terms, the medians are 12.3% (asteroseismology) and 18.3% (gyrochronology). Notably, these cross-publication scatters exceed the median reported statistical uncertainties of the individual measurements, which are 9% and 16% respectively. The implication is that quoted statistical errors systematically understate total uncertainty, reinforcing the value of compiling heterogeneous literature ages as a check on any single analysis.

The authors also quantified the impact of retaining near-duplicate gyrochronology entries by recomputing summary statistics using only the most recent application of each empirical relation; the resulting median average age and standard deviation (2.24 Gyr, 0.37 Gyr) differ negligibly from the full-catalog values, supporting their inclusion policy.

Consistency between methods

For the 14 stars with both asteroseismic and gyrochronal ages, the two methods agree reasonably well for stars younger than about 6 Gyr, with a median difference relative to the asteroseismic age of approximately −13%. Beyond that age, gyrochronology substantially underestimates ages, with a median discrepancy of −47%, consistent with the expected onset of weakened magnetic braking and flattening of the age-rotation relation. This result has a practical consequence: gyrochronal ages alone cannot be trusted for old HWO targets, precisely the population most relevant for assessing long-term habitability.

Prospects for improving coverage

Cross-matching with the TESS legacy sample of bright solar-like oscillators reveals 133 Tier 1/2 stars (20% of the sample) with detected oscillations, of which 116 currently lack asteroseismic ages in the catalog — a concrete near-term opportunity. The PLATO mission, planned for launch in 2026, will provide long-baseline photometry for roughly one million stars and is projected to recover rotation periods for over 70% of observed stars within six months and over 90% within four years, addressing the limitation that TESS's 27.4-day sectors reliably recover only periods shorter than about 10–12 days. The TESS All-Sky Rotation Survey provides periods for roughly 900,000 stars within 500 pc, including 30 Tier 1/2 stars, 22 of which lack gyrochronal ages.

The paper also discusses chemical clocks ([Y/Mg], [Y/Al]) as a possible future addition, noting they achieve roughly 1 Gyr precision for solar twins but that bright solar twins in the sample are often the calibration stars themselves. A notable application is the binary solar twins $\zeta^1$ Ret and $\zeta^2$ Ret, whose chromospheric and isochronal ages (2–5 Gyr) conflict with Galactic kinematics indicating old-disk membership; [Y/Mg] ages of $9.1 \pm 0.5$ and $9.4 \pm 0.5$ Gyr resolve this tension, consistent with a blue straggler origin via binary coalescence.

Limitations and open questions

Several caveats bear directly on how the catalog should be used. The unweighted averages and standard deviations reported in the overview table conflate methodological differences among pipelines with intrinsic measurement error, since the variance of reported central values contains contributions from both; the authors make no attempt to disentangle these. The systematic-uncertainty estimates rest on small samples — particularly for asteroseismology, where multi-measurement stars are few. Coverage is effectively absent for M dwarfs: no pulsating M dwarf has been detected, and detecting oscillations may require precision approaching 1 ppm beyond current instrumentation, leaving open whether PLATO or extreme-precision radial velocity monitoring will enable asteroseismology for the lowest-mass HWO targets. The gyrochronology shortfall at old ages remains unresolved pending wider application of gyro-kinematic relations. Finally, the target list itself is provisional; the authors commit to adding future tier updates without removing reclassified stars, but the catalog's completeness relative to the eventual HWO target set depends on decisions not yet made.

Conclusion

The HAges Catalog provides a curated, reproducible compilation of high-precision published ages for the 659 stars most likely to be observed by HWO, together with empirically grounded estimates of systematic uncertainty: roughly 12% for asteroseismology and 18% for gyrochronology based on inter-publication scatter. Its principal finding is quantitative and sobering — only about 5% of priority targets have asteroseismic ages, about 17–20% have gyrochronal ages, and about 2% have both — establishing a clear observational deficit that TESS, PLATO, and gyro-kinematic methods can partially address before launch. As a living resource updated approximately yearly, it is positioned to serve as the reference point for tracking progress toward the age precision that biosignature interpretation will require.