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| Paper: |
Masses of Potentially Habitable Planets Characterized by the Habitable Worlds Observatory |
| Monograph: |
10, HWO25 Proceedings Part I: Community Science Case Development Documents |
| Page: |
365 |
| Authors: |
Kaz Gary; B. Scott Gaudi; Eduardo Bendek; Ty Robinson; Renyu Hu; Breann Sitarski; Aki Roberge; Eric Mamajek |
| DOI: |
10.26624/UFTJ9431 |
| Abstract: |
Constraints on the masses of exoplanets directly imaged and characterized by the Habitable Worlds
Observatory (HWO) are crucial for categorizing these planets and interpreting their spectra. In particular,
achieving a mass measurement with a precision of approximately 10% or better may be necessary to identify
the dominant gaseous species in the atmospheres of Earth-like planets. This, in turn, is essential for assessing
their potential habitability and interpret potential biosignatures (Damiano et al. 2025). Space-based astrometry
will be required to measure the masses of planets in face-on systems, or planets orbiting hot and rapidly
rotating or highly active stars. Astrometric uncertainties are dominated by the number and magnitude of
background reference stars needed to precisely measure the astrometric wobble of the target star induced by
the planet. To that end, we propose a program to measure the masses of Earth analogs orbiting HWO target
stars with ultra-high-precision astrometry obtained with the HWO high-resolution instrument. We assess the
photon-noise error budget for these observations. We find that, for a field of view spanning a few square
arcminutes, the astrometric uncertainty due to the number and brightness of reference stars dominates the
photon-noise error budget, particularly for targets near the Galactic poles. We explored the impact of filter
choice and location in the sky on the photon-noise astrometric uncertainties by simulating the magnitude
distribution of reference stars across different filters at a range of galactic longitudes and latitudes. We find
that a ∼200-day survey in the Gaia G band consisting of 100 epochs per target star distributed over the 5-year
prime mission with a 6m aperture HWO equipped with a 6′×6′ field-of-view would be required to achieve
the photon-noise sensitivity to measure the masses of the ∼40 Earth-mass habitable-zone planets to ∼10%. |
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