Determining the astrophysical noise floor of the Habitable Worlds Observatory’s coronagraphs

The Habitable Worlds Observatory will use a coronagraph to block starlight and reveal faint, potentially Earth-like planets around nearby stars, and to spectrally characterize them in search of oxygen, requiring SNR > 10. Achieving this science goal demands suppressing and subtracting residual starlight to a few parts in 10¹². The challenge is often framed primarily in terms of telescope and instrument stability, the dominant engineering driver for HWO. However, many coronagraphs capable of 10⁻¹⁰ raw contrast are sensitive to details of the astrophysical scene (stellar angular diameter, hot exozodiacal dust, and starspots), which can introduce residual structure in the PSF potentially limiting starlight subtraction to levels above the required few parts in 10¹² and imposing an astrophysical, rather than instrumental, noise floor. Here we present estimates of this astrophysical noise floor with the baselined HWO coronagraph (AAVC) and evaluate two subtraction techniques: RDI and ADI.