Abstract
Abstract Through the Backyard Worlds: Planet 9 citizen science project, we have identified a wide-separation (∼10′, ∼9900 au projected) substellar companion to the nearby (∼17.5 pc), mid-M dwarf Ross 19. We have developed a new formalism for determining chance alignment probabilities based on the BANYAN Σ tool, and find a 100% probability that this is a physically associated pair. Through a detailed examination of Ross 19A, we find that the system is metal-poor ([Fe/H] = −0.40 ± 0.12) with an age of 7.2 − 3.6 + 3.8 Gyr. Combining new and existing photometry and astrometry, we find that Ross 19B is one of the coldest known wide-separation companions, with a spectral type on the T/Y boundary, an effective temperature of 500 − 100 + 115 K, and a mass in the range 15–40 M Jup. This new, extremely cold benchmark companion is a compelling target for detailed characterization with future spectroscopic observations using facilities such as the Hubble Space Telescope or James Webb Space Telescope.
Highlights
Brown dwarfs and giant planets never settle onto a stable position in color–magnitude diagrams; instead, they radiatively cool along evolutionary tracks that are degenerate in mass, metallicity, luminosity, and age (e.g., Burrows et al 2001)
We have presented the discovery of an extremely cold companion to the nearby M star Ross 19
Based on new astrometry for this cold companion and a modified BANYAN Σ (Gagné et al 2018a) routine for co-moving companions, we find the likelihood that these two objects are a bound pair is 100%
Summary
Brown dwarfs and giant planets never settle onto a stable position in color–magnitude diagrams; instead, they radiatively cool along evolutionary tracks that are degenerate in mass, metallicity, luminosity, and age (e.g., Burrows et al 2001). Y-type objects have been spectroscopically confirmed (Cushing et al 2011; Kirkpatrick et al 2012; Liu et al 2012; Tinney et al 2012; Kirkpatrick et al 2013; Cushing et al 2014; Luhman 2014; Pinfield et al 2014; Dupuy et al 2015; Schneider et al 2015; Leggett et al 2017; Martin et al 2018; Tinney et al 2018) Benchmark companions at these extremely cold temperatures and low masses are rarer still. We describe the discovery of Ross 19B, as well as observations and analyses we have performed to characterize both the A and B components of this system
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