HIP 39017 b

Subject: HIP 39017 b 8th March 2024, 4:23 am

Direct Imaging Discovery of a Substellar Companion Orbiting the Accelerating Variable Star, HIP 39017
https://arxiv.org/abs/2403.04000

Quote :: We present the direct imaging discovery of a substellar companion (a massive planet or low-mass brown dwarf) to the young, γ Doradus-type variable star, HIP 39017 (HD 65526). The companion's SCExAO/CHARIS JHK (1.1−2.4μm) spectrum and Keck/NIRC2 L′ photometry indicate that it is an L/T transition object. A comparison of the JHK+L′ 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 semi-major axis of 23.8+8.7−6.1 au, a dynamical companion mass of 30+31−12~MJ, 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 MJ 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+9.1−7.4~MJ and a mass ratio of ∼1.4\%. Analysis of the host star's multi-frequency γ Dor-type pulsations, astrometric monitoring of HIP 39017b, and Gaia DR4 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.