학술논문
Direct-imaging Discovery of a Substellar Companion Orbiting the Accelerating Variable Star HIP 39017
Document Type
article
Author
Taylor L. Tobin; Thayne Currie; Yiting Li; Jeffrey Chilcote; Timothy D. Brandt; Brianna Lacy; Masayuki Kuzuhara; Maria Vincent; Mona El Morsy; Vincent Deo; Jonathan P. Williams; Olivier Guyon; Julien Lozi; Sebastien Vievard; Nour Skaf; Kyohoon Ahn; Tyler Groff; N. Jeremy Kasdin; Taichi Uyama; Motohide Tamura; Aidan Gibbs; Briley L. Lewis; Rachel Bowens-Rubin; Maïssa Salama; Qier An; Minghan Chen
Source
The Astronomical Journal, Vol 167, Iss 5, p 205 (2024)
Subject
Language
English
ISSN
1538-3881
Abstract
We present the direct-imaging discovery of a substellar companion (a massive planet or low-mass brown dwarf) to the young, γ Doradus ( γ Dor)-type variable star HIP 39017 (HD 65526). The companion’s SCExAO/CHARIS JHK (1.1–2.4 μ m) spectrum and Keck/NIRC2 $L^{\prime} $ photometry indicate that it is an L/T transition object. A comparison of the JHK + L $^{\prime} $ spectrum to several atmospheric model grids finds a significantly better fit to cloudy models than cloudless models. Orbit modeling with relative astrometry and precision stellar astrometry from Hipparcos and Gaia yields a semimajor axis of ${23.8}_{-6.1}^{+8.7}$ au, a dynamical companion mass of ${30}_{-12}^{+31}$ M _J , and a mass ratio of ∼1.9%, properties most consistent with low-mass brown dwarfs. However, its mass estimated from luminosity models is a lower ∼13.8 M _J due to an estimated young age (≲115 Myr); using a weighted posterior distribution informed by conservative mass constraints from luminosity evolutionary models yields a lower dynamical mass of ${23.6}_{-7.4}^{+9.1}$ M _J and a mass ratio of ∼1.4%. Analysis of the host star’s multifrequency γ Dor-type pulsations, astrometric monitoring of HIP 39017 b, and Gaia Data Release 4 astrometry of the star will clarify the system age and better constrain the mass and orbit of the companion. This discovery further reinforces the improved efficiency of targeted direct-imaging campaigns informed by long-baseline, precision stellar astrometry.