OASIS Survey Direct Imaging and Astrometric Discovery of HIP 71618 B: A Substellar Companion Suitable for the Roman Coronagraph Technology Demonstration

TL;DR

This paper reports the discovery and characterization of a substellar companion to HIP 71618, demonstrating its suitability as a target for the Roman Space Telescope's coronagraph technology demonstration through astrometry, imaging, and modeling.

Contribution

The study combines astrometry and high-contrast imaging to discover and characterize HIP 71618 B, highlighting its potential for Roman Coronagraph testing and providing detailed orbital and atmospheric properties.

Findings

HIP 71618 B is a substellar companion with a mass around 60-65 Jupiter masses.

The companion has a nearly edge-on orbit at 11 au with high eccentricity.

HIP 71618 B is a promising target for Roman Coronagraph's dark hole demonstration.

Abstract

We present the OASIS survey program discovery of a substellar companion orbiting the young A1V star HIP 71618, detected using precision astrometry from Gaia and Hipparcos and high-contrast imaging with SCExAO/CHARIS and Keck/NIRC2. Atmospheric modeling favors a spectral type of M5--M8 and a temperature of $\sim$2700 $\pm$ 100 $K$. Dynamical modeling constrains HIP 71618 B's mass to be ${60}_{-21}^{+27}$ $M_{\rm Jup}$ or ${65}_{-29}^{+54}$ $M_{\rm Jup}$, depending on the adopted companion mass prior. It has a nearly edge-on, 11 au-orbit with a high eccentricity. HIP 71618 B will be located within Roman Coronagraph's dark hole region during the instrument's technological demonstration phase. A high signal-to-noise ratio detection of HIP 71618 B at 575 nm would demonstrate a 5-$\sigma$ contrast of 10$^{-7}$ or better. The system is also located within or very close to Roman's Continuous Viewing Zone -- near multiple candidate reference stars for dark-hole digging -- and its primary is bright ($V$ $\approx$ 5). The suitability of HIP 71618 as one potential Roman Coronagraph target for demonstrating the instrument's core requirement (TTR5) should motivate the timely, deep vetting of candidate reference stars.