CoronaGraph Instrument Reference stars for Exoplanets (CorGI-REx) I. Preliminary Vetting and Implications for the Roman Coronagraph and Habitable Worlds Observatory

TL;DR

This paper evaluates potential reference stars for the Roman Coronagraph and Habitable Worlds Observatory, focusing on their suitability based on brightness, size, and multiplicity, to optimize high-contrast exoplanet imaging.

Contribution

It provides a vetted list of 58 reference star candidates and discusses their suitability for space-based high-contrast imaging missions.

Findings

Identified 40 primary and 18 reserve reference stars relevant to Roman and HWO.

High-resolution imaging showed no new stellar companions among candidates.

Highlighting the need for higher-contrast observations for better vetting.

Abstract

The upcoming Roman Coronagraph will be the first high-contrast instrument in space capable of high-order wavefront sensing and control technologies, a critical technology demonstration for the proposed Habitable Worlds Observatory (HWO) that aims to directly image and characterize habitable exoEarths. The nominal Roman Coronagraph observing plan involves alternating observations of a science target and a bright, nearby reference star. High contrast is achieved using wavefront sensing and control, also known as "digging a dark hole", where performance depends on the properties of the reference star, requiring V<3, a resolved stellar diameter <2 mas, and no stellar multiplicity. The imposed brightness and diameter criteria limit the sample of reference star candidates to high-mass main sequence and post-main sequence objects, where multiplicity rates are high. A future HWO coronagraph may have similarly restrictive criteria in reference star selection. From an exhaustive literature review of 95 stars, we identify an initial list of 40 primary and 18 reserve reference star candidates relevant to both the Roman Coronagraph and HWO. We present results from an initial survey of these candidates with high-resolution adaptive optics imaging and speckle interferometry and identify no new companions. We discuss the need for higher-contrast observations to sufficiently vet these reference star candidates prior to Roman Coronagraph observations along with the implications of reference star criteria on observation planning for Roman and HWO.