SCExAO/CHARIS Direct Imaging of A Low-mass Companion At A Saturn-like Separation from an Accelerating Young A7 Star
Currie, Thayne; Kwon, Jungmi; Tamura, Motohide; Wagner, Kevin; Kuzuhara, Masayuki; Brandt, Timothy D.; Akiyama, Eiji; Chilcote, Jeffrey; Guyon, Olivier; Janson, Markus; Jovanovic, Nemanja; Lozi, Julien; McElwain, Michael W.; Tobin, Taylor; Groff, Tyler D.; Sahoo, Ananya; Deo, Vincent; Skaf, Nour; Nishikawa, Jun; Knapp, Jill; Hełminiak, Krzysztof
United States, Japan, Sweden, Poland, France
Abstract
We present the SCExAO direct imaging discovery and characterization of a low-mass companion to the nearby young A7IV star, HD 91312. SCExAO/CHARIS JHK (1.1-2.4 μm) spectra and SCExAO/HiCIAO H-band imaging identify the companion over a two year baseline in a highly inclined orbit with a maximum projected separation of 8 au. The companion, HD 91312 B, induces an 8.8σ astrometric acceleration on the star as seen with the Gaia & Hipparcos satellites and a long-term radial-velocity trend as previously identified by Borgniet et al. HD 91312 B's spectrum is consistent with that of an early-to-mid M dwarf. Hipparcos and Gaia absolute astrometry, radial-velocity data, and SCExAO/CHARIS astrometry constrain its dynamical mass to be ${0.337}_{-0.044}^{+0.042}$ M ⊙, consistent with - but far more precise than - masses derived from spectroscopy, and favors a nearly edge-on orbit with a semimajor axis of ~9.7 au. This work is an example of precisely characterizing properties of low-mass companions at solar system-like scales from a combination of direct imaging, astrometry, and radial-velocity methods.