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

This paper presents the HAges Catalog, a living resource compiling precise stellar ages for 659 high-priority Habitable Worlds Observatory targets based on asteroseismology and gyrochronology, while highlighting the current scarcity of such data and the urgent need for further age constraints to support future exoplanet characterization.

Original authors: Austin T. Ware, Katelyn Ruppert, Patrick A. Young

Published 2026-05-14

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CC BY 4.0

Original authors: Austin T. Ware, Katelyn Ruppert, Patrick A. Young

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the Habitable Worlds Observatory (HWO) as a massive, high-tech camera crew preparing to film a documentary about alien life. Before they can point their lenses at a specific star to look for Earth-like planets, they need to know the "age" of that star. Why? Because a star's age tells us how much time its planets have had to develop life, and whether that life is still around or has already faded away.

The problem is that figuring out a star's age is like trying to guess the age of a person just by looking at them from a distance. It's incredibly difficult, and different experts often give different answers.

This paper introduces the HAges Catalog (pronounced like "haggis," the Scottish dish), which is essentially a massive, organized "ID card" database for the 659 stars that the HWO is most likely to photograph. Here is what the authors did, explained simply:

1. The Goal: A "Living" Guest List

The authors created a catalog of ages for the "Tier 1" and "Tier 2" stars—the VIPs on the HWO's hit list. They didn't just make up numbers; they went through thousands of scientific papers to find ages that had already been calculated by other scientists using two specific, high-precision methods.

Think of this catalog as a living guest list. It's not a static book; the authors promise to keep updating it regularly as new information comes in before the telescope launches.

2. The Two "Clocks" Used

To figure out the stars' ages, the paper focuses on two main methods, which act like different types of clocks:

Asteroseismology (The "Heartbeat" Clock):
Imagine a star is like a giant bell. When it rings, it vibrates in specific patterns. By listening to these vibrations (changes in brightness or movement), scientists can hear the star's internal structure. This is the "gold standard" for accuracy.
- The Catch: It's like trying to hear a bell ring in a noisy room. It's very hard to do for most stars, so only a tiny fraction (about 5%) of the VIP stars have this "heartbeat" age recorded.
Gyrochronology (The "Spin" Clock):
Stars are born spinning fast, but as they get older, they slow down, much like a spinning top losing momentum. This happens because the star's magnetic field acts like a brake, dragging on its own solar wind. By measuring how fast a star is spinning, scientists can estimate its age.
- The Catch: This clock is less precise for very young stars (who spin all over the place) and very old stars (who slow down so much the clock gets fuzzy). About 20% of the VIP stars have a "spin" age.

3. The Big Discovery: We Are Missing Most of the Data

The authors looked at their list of 659 stars and found a major gap:

Only 5% have a "heartbeat" age.
Only 20% have a "spin" age.
Only 2% have both.

It's like having a guest list for a party, but you only know the birthdates of a few people. For the vast majority of the stars the telescope will look at, we simply don't know their ages well enough yet.

4. How Reliable Are These Clocks?

The paper also checked how much the different experts agreed with each other.

When multiple scientists measured the same star's "heartbeat," their answers were usually very close (within about 12% of each other).
When they measured the "spin," the answers varied a bit more (about 18% difference).
Crucially, the authors found that the "official" error margins scientists usually report are often too optimistic. The real uncertainty (the systematic error) is usually larger than the math says it is.

5. The Future: Filling the Gaps

The paper concludes that we need a "concerted effort" (a team-wide push) to measure these ages before the telescope launches.

New Tools: The authors mention that the TESS and PLATO space missions are like new, super-sensitive microphones and cameras that will help us hear the "heartbeats" of more stars and measure their "spins" more accurately.
The Plan: They have identified 133 stars in the VIP list that TESS has already detected vibrating but for which we don't have a calculated age yet. These are the top priorities for future study.

In a nutshell: The authors built a master list of the stars the next big space telescope will study. They found that while we have some good age estimates for a few, we are missing ages for most of them. This catalog is a tool to show the scientific community exactly where the gaps are, so they can go out and fill them before the telescope starts its search for alien life.

Technical Summary: The HAges Catalog

Problem Statement
Precise stellar ages, with uncertainties $\lesssim$ 1 Gyr (approximately 20% at solar age), are critical for the Habitable Worlds Observatory (HWO) mission. These measurements are required to discern evolutionary trends in atmospheric biosignatures of terrestrial habitable zone exoplanets and to constrain planetary interior evolution, such as mantle degassing lifetimes. However, precise stellar ages are notoriously difficult to obtain, and existing literature often lacks the necessary precision or consistency for the high-priority targets identified for HWO. Specifically, there is a need for a consolidated resource of ages derived from high-precision methods to aid in target prioritization and system characterization.

Methodology
The authors present the HAges Catalog, a compilation of published stellar ages for the Tier 1 and Tier 2 targets in the HWO Target Stars and Systems (TSS) sub-working group's TSS25 list. This sample comprises 659 stars, representing the targets most likely to be observed by HWO regardless of the final mission architecture.

The catalog construction involved a manual literature search using the NASA Astrophysics Data System (ADS) and unique SIMBAD identifiers for each target. The authors focused on two state-of-the-art age-dating methods:

Asteroseismology: Utilizing stellar oscillations to constrain interior structure and evolution. The authors recorded ages derived from both global scaling relations and detailed modeling of individual oscillation frequencies. They contacted authors to resolve ambiguities regarding preferred results when multiple pipelines or models were discussed without a clear selection.
Gyrochronology: Relating measured rotation periods to age via magnetic braking. The authors required that ages be derived from measured rotation periods obtained via periodogram analysis, excluding estimates based solely on chromospheric activity indices ( $R'_{HK}$ ) or $v \sin i$ to minimize uncertainty. They also required traceability to original sources for reproducibility.

The catalog excludes specific known erroneous results (e.g., an erroneous age for $\gamma$ Pav due to mode misidentification and specific gyrochronology ages for 51 Peg based on spurious rotation periods). The resulting resource is structured as a "living document," intended to be updated annually with new measurements and additions to the target list, though no stars are ever removed even if their priority tier changes.

Key Results

Sample Coverage: The catalog currently contains 490 stellar ages for 127 stars, representing approximately 19% of the 659-star sample.
- Asteroseismology: 164 ages for 31 stars ( $\sim$ 5% of the sample).
- Gyrochronology: 326 ages for 110 stars ( $\sim$ 17% of the sample).
- Overlap: Only 14 stars ( $\sim$ 2%) have constraints from both methods.
Uncertainty Analysis:
- For stars with multiple published measurements, the median reported statistical uncertainties are slightly smaller than the systematic uncertainties (scatter between published values).
- Asteroseismology: Median statistical uncertainty is $\sim$ 9%, while the median systematic uncertainty (scatter) is $\sim$ 12% (0.64 Gyr).
- Gyrochronology: Median statistical uncertainty is $\sim$ 16%, while the median systematic uncertainty is $\sim$ 18% (0.4 Gyr).
- Systematic uncertainties in gyrochronology are generally larger for the youngest and oldest stars, where the method is less precise.
Method Comparison: For stars $\lesssim$ 6 Gyr, asteroseismic and gyrochronal ages are generally consistent (median difference $\sim$ -13%). For older stars, gyrochronology tends to significantly underestimate ages relative to asteroseismology (median difference $\sim$ -47%), attributed to the observed flattening of the rotation-age relation due to weakened magnetic braking in older stars.
Future Data Availability: Cross-matching with recent TESS data reveals that 133 stars (20% of the sample) have detected solar-like oscillations but lack asteroseismic ages in the current catalog. Similarly, 22 Tier 1/2 stars have measured rotation periods from TESS but lack derived gyrochronology ages.

Significance and Claims
The paper claims that the HAges Catalog serves as a vital, community-accessible resource (hosted on Zenodo) to highlight stars most in need of precise age measurements. By compiling existing high-precision data, the catalog:

Provides summary statistics and detailed individual measurements for HWO targets.
Quantifies the current scarcity of precise ages, noting that over 80% of the sample lacks precise ages from either method.
Highlights the necessity for a concerted effort to obtain robust age constraints in advance of the HWO mission.
Serves as a baseline for future updates, with the authors noting that upcoming missions like TESS and PLATO, along with improved gyro-kinematic relations, will likely expand the availability of precise ages for these targets.

The authors emphasize that the catalog is intended to be a "living resource" that will be regularly updated to support the HWO mission's target selection and scientific goals.

1. The Goal: A "Living" Guest List

2. The Two "Clocks" Used

3. The Big Discovery: We Are Missing Most of the Data

4. How Reliable Are These Clocks?

5. The Future: Filling the Gaps

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