SCExAO/CHARIS High-Contrast Pre-Launch Vetting of Roman Coronagraph Technology Demonstration PSF Reference Stars

Abstract

We present deep, SCExAO/CHARIS high-contrast integral field spectroscopy and archival imaging of four candidate Roman Coronagraph PSF reference stars within/near the Roman Continuous Viewing Zone and potentially suitable for the Coronagraph's key technology demonstration targets HIP 71618 and HIP 54515. For CHARIS data, we achieve 5-$\sigma$ contrasts down to $\sim$1.4$\times$10${}^{-5}$, $\sim$6$\times$10${}^{-6}$, and 10${}^{-6}$ to 4$\times$10${}^{-7}$ at 0\farcs{}16, 0\farcs{}25, and 0\farcs{}5 to 1\arcsec{}. Companion mass limits rule out brown dwarfs at $\rho$ $\sim$ 0\farcs{}15--0\farcs{}25 and massive planets at wider separations around all targets. More critically, for three of the four references our analysis disfavors companions with $V$ band contrasts brighter than 10${}^{-8}$, 10${}^{-9}$, and $10^{-10}$ at 0\farcs{}15, 0\farcs{}3, and 1$\arcsec{}$. Unless these targets have faint substellar companions within $\rho$ $\sim$ 0\farcs{}15, they likely lack background stars or companions that could corrupt the Roman Coronagraph's dark hole digging to preclude detecting reflected-light planets. For $\alpha$ Cep, our limits are a factor of $\sim$10 worse but still meet the TTR5 limit of 10${}^{-7}$ beyond $\rho$ $\sim$ 0\farcs{}25: beyond 0\farcs{}4, they exclude a Jupiter-twin reflected-light companion (10${}^{-9}$). Archival Keck/NIRC2 data likewise find no substellar companions with $\Delta$V $>$ 10${}^{-8}$ at wider separations. Finally, we assess the observability of HIP 71618 and HIP 54515 -- updated for Roman's launch date of August 30, 2026. Adding $\gamma$ Boo -- not currently in the Roman CPP team reference-star list -- would improve schedulability for the tech demo's key targets.

12 pages, 6 figures, 3 tables; first extreme AO-depth vetting of Roman Coronagraph PSF reference stars