The Ultracool SpeXtroscopic Survey. I. Volume-limited Spectroscopic Sample and Luminosity Function of M7−L5 Ultracool Dwarfs

• Published in: The Astrophysical journal Vol. 883; no. 2; pp. 205 - 239
• Main Authors: Bardalez Gagliuffi, Daniella C., Burgasser, Adam J., Schmidt, Sarah J., Theissen, Christopher, Gagné, Jonathan, Gillon, Michael, Sahlmann, Johannes, Faherty, Jacqueline K., Gelino, Christopher, Cruz, Kelle L., Skrzypek, Nathalie, Looper, Dagny
• Format: Journal Article Web Resource
• Language: English
• Published: Philadelphia The American Astronomical Society 01-10-2019; IOP Publishing; Institute of Physics Publishing
• Subjects: astronomical databases: miscellaneous; Astrophysics; Aérospatiale, astronomie & astrophysique; binaries: close; binaries: general; brown dwarfs; Color; Completeness; Data analysis; Distance measurement; Gravitation; Hydrogen; infrared: stars; Luminosity; Near infrared radiation; Outliers (statistics); Physical, chemical, mathematical & earth Sciences; Physique, chimie, mathématiques & sciences de la terre; Polls & surveys; Space science, astronomy & astrophysics; Spectra; Spectroscopy; Spectrum analysis; stars: fundamental parameters
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.3847/1538-4357/ab253d

We present a volume-limited, spectroscopically verified sample of M7−L5 ultracool dwarfs (UCDs) within 25 pc. The sample contains 410 sources, of which 93% have trigonometric distance measurements (80% from Gaia DR2) and 81% have low-resolution (R ∼ 120), near-infrared (NIR) spectroscopy. We also present an additional list of 60 sources that may be M7−L5 dwarfs within 25 pc when distance or spectral-type uncertainties are taken into account. The spectra provide NIR spectral and gravity classifications, and we use these to identify young sources, red and blue J − KS color outliers, and spectral binaries. We measure very low gravity and intermediate-gravity fractions of and , respectively; fractions of red and blue color outliers of and , respectively; and a spectral binary fraction of . We present an updated luminosity function for M7−L5 dwarfs continuous across the hydrogen-burning limit that agrees with previous studies. We estimate our completeness to range between 69% and 80% when compared to an isotropic model. However, we find that the literature late-M sample is severely incomplete compared to L dwarfs, with completeness of and , respectively. This incompleteness can be addressed with astrometric-based searches of UCDs with Gaia to identify objects previously missed by color- and magnitude-limited surveys.