HWO Target Stars and Systems: A Prioritized Community List of Potential Stellar Targets for the Habitable Worlds Observatory's ExoEarth Survey

TL;DR

The paper introduces the HWO Target Stars and Systems 2025 (TSS25) catalog, a community-driven, tiered list of candidate targets for the Habitable Worlds Observatory exoEarth survey. It integrates prior star catalogs (HPIC, ExEP) and multiple exoplanet yield analyses across diverse mission architectures to identify stars most likely to be observed and to guide precursor observations. The authors define three tiers (Tier 1–3) with tier-specific observational requirements and provide public access to the living catalog, including 659 high-priority Tier 1+2 targets and a broad Tier 3 input sample for yield modeling. This framework enables coordinated precursor programs to maximize the mission’s science return and accommodate evolving mission designs.

Abstract

The HWO Target Stars and Systems 2025 (TSS25) list is a community-developed catalog of potential stellar targets for the Habitable Worlds Observatory (HWO) in its survey to directly image Earth-sized planets in the habitable zone. The TSS25 list categorizes potential HWO targets into priority tiers based on their likelihood to be surveyed and the necessity of obtaining observations of their stellar properties prior to the launch of the mission. This target list builds upon previous efforts to identify direct imaging targets and incorporates the results of multiple yield calculations assessing the science return of current design concepts for HWO. The TSS25 list identifies a sample of target stars that have a high probability to be observed by HWO (Tiers 1 and 2), independent of assumptions about the mission's final architecture. These stars should be the focus of community precursor science efforts in order to mitigate risks and maximize the science output of HWO. This target list is publicly available and is a living catalog that will be continually updated leading up to the mission.

Figures (4)

• Figure 1: Stars selected by the AYO Stark24 8m LUVOIR B yield calculation (left) and the 6m "scenario F" yield calculation (right) in distance vs. luminosity space. Points are color coded based on the fraction of simulations in which each star was selected. Gray points in the background are the stars in the HPIC Tuchow24.
• Figure 2: Stars selected by the ensemble of EXOSIMS calculations of Morgan24 in distance vs. luminosity space. Points are color coded based on the yield of exoEarths per star, averaged over an ensemble of scenarios, and averaged over the yield in the visible, IR, and UV bands to define a "panchromatic yield metric". Gray points in the background are the stars in the HPIC. Note that these calculations used Exocat as an input catalog rather than the HPIC, which had a distance cutoff at 30 pc instead of the 50 pc for the HPIC.
• Figure 3: Targets in all tiers of our catalog plotted in distance vs. luminosity space, with the tiers indicated by color.
• Figure 4: Histogram of Johnson V band magnitudes for stars in each tier of the TSS25 list.