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Provisional NASA ExEP Mission Target Star List for the Habitable Worlds Observatory

Presentation #628.17 in the session Future Missions and Instrumentation.

Published onApr 03, 2024
Provisional NASA ExEP Mission Target Star List for the Habitable Worlds Observatory

Informed by the science cases and options for the LUVOIR and HabEx NASA mission concepts, we present here a summary of an independent analysis by the NASA Exoplanet Exploration Program (ExEP) Science Office to produce a list of priority target stars amenable to surveys for potentially habitable exoplanets via imaging with the ~6-m Habitable Worlds Observatory (HWO) concept recommended by Astro2020. It is hoped that this target list will stimulate investigations of the properties of these stars, and long-term monitoring of exoplanets in their systems, to ultimately inform future HWO target prioritization and inform the modeling and interpretation of exoplanet spectra. To achieve the Decadal goal to “provide a robust sample of ~25 atmospheric spectra of potentially habitable exoplanets,” the observatory will have severe constraints on its survey capability given the limited number of nearby stars whose habitable zones (HZs) will be accessible to starlight suppression techs (e.g. coronagraph, starshade), and whose small planets will be bright enough to measure spectra on reasonable timescales. From a compiled input sample of ~800 nearby stars, we conducted a thorough literature search for their basic properties and calculated magnitudes and angular separations for hypothetical small HZ planets. By consideration of the brightnesses, planet-star brightness ratios, and angular separations of hypothetical planets placed at various phase angles and orbital radii in the HZ, we iteratively down-selected stars that would have the brightest exo-Earths at the widest angular separations until ~100 cumulative HZs were surveyed. The stars have mean(rms) values of: V = 5.2(1.0)mag, Rc = 4.8(0.9)mag, Dist = 13(5)pc, Teff = 5700(700)K, [Fe/H] = -0.1(0.2)dex, mass = 1.0(0.2)MSun, log(L/LSun) = 0.0(0.5) dex. All are brighter than V < 7.5 and Rc < 6.4, with types between F1V and M2V, and maximum distances by spectral class of 4pc(M), 13pc(K), 21pc(G), and 24pc(F). Given reasonable assumptions about achievable exoplanet brightnesses and planet-star-brightness ratios, to get to ~100 cumulative HZs surveyed, one requires a starlight suppression solution that enables detection and spectral characterization of exo-Earths down to inner working angles (IWAs) of ~60-70 mas. The peer-reviewed ExEP target star catalog is posted at the NASA Exoplanet Archive (https://exoplanetarchive.ipac.caltech.edu/) under “HWO ExEP Precursor Science Stars” and the documentation is posted on the ExEP science site: https://exoplanets.nasa.gov/exep/science-overview/.

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