TOI 694 b and TIC 220568520 b: Two Low-Mass Companions Near the Hydrogen Burning Mass Limit Orbiting Sun-like Stars

• Main Authors: Mireles, Ismael, Shporer, Avi, Grieves, Nolan, Zhou, George, Günther, Maximilian N, Brahm, Rafael, Ziegler, Carl, Stassun, Keivan G, Huang, Chelsea X, Nielsen, Louise, Santos, Leonardo A. dos, Udry, Stéphane, Bouchy, François, Ireland, Michael, Wallace, Alexander, Sarkis, Paula, Henning, Thomas, Jordan, Andres, Law, Nicholas, Mann, Andrew W, Paredes, Leonardo A, James, Hodari-Sadiki, Jao, Wei-Chun, Henry, Todd J, Butler, R. Paul, Rodriguez, Joseph E, Yu, Liang, Flowers, Erin, Ricker, George R, Latham, David W, Vanderspek, Roland, Seager, Sara, Winn, Joshua N, Jenkins, Jon M, Furesz, Gabor, Hesse, Katharine, Quintana, Elisa V, Rose, Mark E, Smith, Jeffrey C, Tenenbaum, Peter, Vezie, Michael, Yahalomi, Daniel A, Zhan, Zhuchang
• Format: Journal Article
• Language: English
• Published: 10-07-2020
• Subjects: Physics - Earth and Planetary Astrophysics; Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.2006.14019

We report the discovery of TOI 694 b and TIC 220568520 b, two low-mass
stellar companions in eccentric orbits around metal-rich Sun-like stars, first
detected by the Transiting Exoplanet Survey Satellite (TESS). TOI 694 b has an
orbital period of 48.05131$\pm$0.00019 days and eccentricity of
0.51946$\pm$0.00081, and we derive a mass of 89.0$\pm$5.3 $M_J$
(0.0849$\pm$0.0051 $M_\odot$) and radius of 1.111$\pm$0.017 $R_J$
(0.1142$\pm$0.0017 $R_\odot$). TIC 220568520 b has an orbital period of
18.55769$\pm$0.00039 days and eccentricity of 0.0964$\pm$0.0032, and we derive
a mass of 107.2$\pm$5.2 $M_J$ (0.1023$\pm$0.0050 $M_\odot$) and radius of
1.248$\pm$0.018 $R_J$ (0.1282$\pm$0.0019 $R_\odot$). Both binary companions lie
close to and above the Hydrogen burning mass threshold that separates brown
dwarfs and the lowest mass stars, with TOI 694 b being 2-$\sigma$ above the
canonical mass threshold of 0.075 $M_\odot$. The relatively long periods of the
systems mean that the magnetic fields of the low-mass companions are not
expected to inhibit convection and inflate the radius, which according to one
leading theory is common in similar objects residing in short-period
tidally-synchronized binary systems. Indeed we do not find radius inflation for
these two objects when compared to theoretical isochrones. These two new
objects add to the short but growing list of low-mass stars with well-measured
masses and radii, and highlight the potential of the TESS mission for detecting
such rare objects orbiting bright stars.