SCExAO/CHARIS Direct Imaging of A Low-mass Companion At A Saturn-like Separation from an Accelerating Young A7 Star

Creators: Chilcote, Jeffrey; Tobin, Taylor; Currie, Thayne; Brandt, Timothy D.; Groff, Tyler D.; Kuzuhara, Masayuki; Guyon, Olivier; Lozi, Julien; Jovanovic, Nemanja; Sahoo, Ananya; Deo, Vincent; Akiyama, Eiji; Janson, Markus; Knapp, Jill; Kwon, Jungmi; McElwain, Michael W.; Nishikawa, Jun; Wagner, Kevin; Hełminiak, Krzysztof; Skaf, Nour; Tamura, Motohide

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.

Additional Information

© 2021. The American Astronomical Society. Received 2021 May 3; revised 2021 September 21; accepted 2021 September 22; published 2021 November 19. We thank the anonymous referee for helpful comments that improved the quality of this paper. The authors wish to acknowledge the very significant cultural role and reverence that the summit of Maunakea holds within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. We wish to acknowledge the critical importance of the current and recent Subaru and Keck Observatory daycrew, technicians, telescope operators, computer support, and office staff employees. Their expertize, ingenuity, and dedication is indispensable to the continued successful operation of these observatories. T.C. was supported by a NASA Senior Postdoctoral Fellowship and NASA/Keck grant LK-2663-948181. We thank the Subaru and NASA Keck Time Allocation Committees for their generous support of this program. The development of SCExAO was supported by JSPS (Grant-in-Aid for Research #23340051, #26220704 & #23103002), Astrobiology Center of NINS, Japan, the Mt Cuba Foundation, and the director's contingency fund at Subaru Telescope. CHARIS was developed under the support by the Grant-in-Aid for Scientific Research on Innovative Areas #2302. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. K.W. acknowledges support from NASA through the NASA Hubble Fellowship grant HST-HF2-51472.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. M.T. is supported by JSPS KAKENHI grant Nos.18H05442, 15H02063, and 22000005. This work was supported by JSPS Grants-in-Aid for Scientic Research, 17K05399 (E.A.).

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