Gaia-4b and 5b: Radial Velocity Confirmation of Gaia Astrometric Orbital Solutions Reveal a Massive Planet and a Brown Dwarf Orbiting Low-mass Stars

Gudmundur Stefansson; Suvrath Mahadevan; Joshua Winn; Marcus Marcussen; Shubham Kanodia; Simon Albrecht; Evan Fitzmaurice; One Mikulskitye; Caleb Cañas; Juan Ignacio Espinoza-Retamal; Yiri Zwart; Daniel Krolikowski; Andrew Hotnisky; Paul Robertson; Jaime A. Alvarado-Montes; Chad Bender; Cullen Blake; Joe Callingham; William Cochran; Megan Delamer; Scott Diddams; Jiayin Dong; Rachel Fernandes; Mark Giovanazzi; Samuel Halverson; Jessica Libby-Roberts; Sarah E Logsdon; Michael McElwain; Joe Ninan; Jayadev Rajagopal; Varghese Reji; Arpita Roy; Christian Schwab; Jason Wright

arXiv · 2410.05654

Gaia-4b and 5b: Radial Velocity Confirmation of Gaia Astrometric Orbital Solutions Reveal a Massive Planet and a Brown Dwarf Orbiting Low-mass Stars

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Abstract

Gaia astrometry of nearby stars is precise enough to detect the tiny displacements induced by substellar companions, but radial velocity data are needed for definitive confirmation. Here we present radial velocity follow-up observations of 28 M and K stars with candidate astrometric substellar companions, which led to the confirmation of two systems, Gaia-4b and Gaia-5b, and the refutation of 21 systems as stellar binaries. Gaia-4b is a massive planet ($M = 11.8 \pm 0.7 \:\mathrm{M_J}$) in a $P = 571.3 \pm 1.4\:\mathrm{day}$ orbit with a projected semi-major axis $a_0=0.312 \pm 0.040\:\mathrm{mas}$ orbiting a $0.644 \pm 0.02 \:\mathrm{M_\odot}$ star. Gaia-5b is a brown dwarf ($M = 20.9 \pm 0.5\:\mathrm{M_J}$) in a $P = 358.58 \pm 0.19\:\mathrm{days}$ eccentric $e=0.6412 \pm 0.0027$ orbit with a projected angular semi-major axis of $a_0 = 0.947 \pm 0.038\:\mathrm{mas}$ around a $0.34 \pm 0.03 \mathrm{M_\odot}$ star. Gaia-4b is one of the first exoplanets discovered via the astrometric technique, and is one of the most massive planets known to orbit a low-mass star.

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Gudmundur Stefansson, Suvrath Mahadevan, Joshua Winn, Marcus Marcussen, Shubham Kanodia, Simon Albrecht, Evan Fitzmaurice, One Mikulskitye, Caleb Cañas, Juan Ignacio Espinoza-Retamal, Yiri Zwart, Daniel Krolikowski, Andrew Hotnisky, Paul Robertson, Jaime A. Alvarado-Montes, Chad Bender, Cullen Blake, Joe Callingham, William Cochran, Megan Delamer, Scott Diddams, Jiayin Dong, Rachel Fernandes, Mark Giovanazzi, Samuel Halverson, Jessica Libby-Roberts, Sarah E Logsdon, Michael McElwain, Joe Ninan, Jayadev Rajagopal, Varghese Reji, Arpita Roy, Christian Schwab, Jason Wright. 2024-10-08. Gaia-4b and 5b: Radial Velocity Confirmation of Gaia Astrometric Orbital Solutions Reveal a Massive Planet and a Brown Dwarf Orbiting Low-mass Stars. https://arxiv.org/abs/2410.05654

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