Abstract
Abstract We report on the characterization of a nearby ( pc) ultracool L dwarf (WISE J192512.78+070038.8; hereafter W1925) identified as a faint (G = 20.038 ± 0.009) object with high proper motion (219.834 ± 1.843 mas yr−1)in the Gaia Data Releases 1 and 2. A Palomar/TripleSpec near-infrared spectrum of W1925 confirms a photometric L7 spectral type previously estimated by Scholz & Bell, and its infrared colors and absolute magnitudes are consistent with a single object of this type. We constructed a spectral energy distribution using the Gaia parallax, literature photometry, and near-infrared spectrum and find a luminosity log(L bol/L ⊙) = −4.443 ± 0.008. Applying evolutionary models, we infer that W1925 is likely a 53 ± 18 M Jup brown dwarf with T eff = 1404 ± 71 K and log g = 5.1 ± 0.4 dex (cgs). While W1925 was detected in both the 2MASS and WISE infrared sky surveys, it was not detected in photographic plate sky surveys. Its combination of extreme optical–infrared colors, high proper motion, and location near the crowded Galactic plane (b = −4.°2) likely contributed to its having evaded detection in pre-Gaia surveys.
Highlights
Despite decades of dedicated searches, the nearby stellar sample (d 25 pc) remains incomplete, for intrinsically faint low-mass stars and brown dwarfs (Henry et al 2018)
We report on the characterization of a nearby (d = 11.2 pc) ultracool L dwarf (WISE J192512.78+070038.8; hereafter W1925) identified as a faint (G = 20.0) high proper motion (0. 22 yr−1) object in the Gaia Data Releases 1 and 2
By (1) counting the number of spectroscopically confirmed L dwarfs outside the Galactic plane (109), (2) calculating the fraction of the total 12 pc volume that is within the Galactic plane (∼ 26%), (3) constructing a probability density function of the space density to predict the number inside the Galactic plane with Bayes theorem based on a Poisson likelihood and a non-informative prior on the space density, and (4) subtracting the number of expected brown dwarfs in the Galactic plane to the number that is detected (22; and including Poisson error bars on this number), yields a predicted 3–12 L dwarfs within 12 pc that remain to be detected in the Galactic plane at a 68% confidence level
Summary
Despite decades of dedicated searches, the nearby stellar sample (d 25 pc) remains incomplete, for intrinsically faint low-mass stars and brown dwarfs (Henry et al 2018). Some of the nearest systems to the Sun, such as the binary brown dwarf WISE J104915.57−531906.1AB at 2.0 pc (3rd closest system to the Sun; hereafter WISE J1049−5319; Luhman 2013) and the Y dwarf WISEA J085510.74−071442.5 at 2.2 pc (4th closest system to the Sun; Luhman 2014a), were only recently uncovered through multi-epoch infrared imaging surveys (see Luhman 2014b) While these surveys, including the Two Micron All Sky survey (2MASS; Skrutskie et al 2006), the Sloan Digital Sky Survey (SDSS; York et al 2000), the UKIRT Infrared Deep Sky Survey (UKIDSS; Lawrence et al 2007), and the Wide-field Infrared Survey Explorer (WISE ; Wright et al 2010) have enabled new discoveries in the Solar neighborhood, few have been made in or near the Galactic plane (e.g. Burgasser et al 2002, Kirkpatrick et al 1999, Kirkpatrick et al 2016, Kirkpatrick et al 2014, Burningham et al 2013, Lucas et al 2010, Gizis et al 2011, Artigau et al 2010, Kuchner et al 2017). Completing the nearby census remains an important goal in stellar population studies
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