RACS: Roman Astrometric Companion Survey
| Program ID | 19028 |
|---|---|
| Science Category | Stellar Physics |
| Program Type | Analysis |
| Category | Medium |
| Principal Investigator | Cheyanne Shariat |
| PI Institution | California Institute of Technology |
| Co-Investigators |
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| Abstract | Roman’s wide-field, high-resolution near-IR imaging will enable the first Galaxy-wide census of resolved stellar companions at sub-arcsecond separations. We propose the Roman Astrometric Companion Survey (RACS), a program to construct a catalog of resolved stellar companions -- including wide binaries (WBs) and tertiaries to inner binaries -- using data from the High-Latitude Wide Area Survey (HLWAS), High-Latitude Time Domain Survey (HLTDS), and Galactic Plane Survey (GPS). Using imaging in low-crowding fields and imaging plus astrometry in crowded fields, RACS will identify physical companions across a wide range of separations, contrasts, and Galactic environments. A core product of RACS will be the empirical calibration of Roman astrometry and grism spectroscopy: because the two stars in a physical WB share a common age, composition, and systemic motion, differences between their measured parallaxes, proper motions, radial velocities, and metallicities directly constrain Roman measurement precision and systematics. This will provide a foundation for the use of Roman stellar measurements. In HLWAS alone, Roman will detect at least 500,000 resolved companions, corresponding to a factor of 10-50 gain over Gaia in the same sky area. This sample will enable large-scale measurements of wide-binary and tertiary fractions across Galactic environment, stellar mass, and metallicity, extending multiplicity studies to smaller separations, fainter companions, and larger distances than were accessible in the Gaia era. It will also reveal wide tertiaries to interacting binaries and compact-object systems, providing new constraints on multiple-star formation, three-body evolution, and the origin of compact binaries. RACS will deliver a public catalog of resolved companions across the Milky Way, providing a lasting resource for Roman and future surveys to explore stellar multiplicity, compact objects, and Galactic structure. |