J/AJ/147/94 Solar neighborhood. XXXII. L and M dwarfs (Dieterich+, 2014) ================================================================================ The solar neighborhood. XXXII. The hydrogen burning limit. Dieterich S.B., Henry T.J., Jao W.-C., Winters J.G., Hosey A.D., Riedel A.R., Subasavage J.P. =2014AJ....147...94D ================================================================================ ADC_Keywords: Stars, dwarfs ; Photometry, VRI ; Parallaxes, trigonometric ; Proper motions ; Effective temperatures ; Photometry, infrared Keywords: brown dwarfs - Hertzsprung-Russell and C-M diagrams - parallaxes - solar neighborhood - stars: fundamental parameters - stars: low-mass Abstract: We construct a Hertzsprung-Russell diagram for the stellar/substellar boundary based on a sample of 63 objects ranging in spectral type from M6V to L4. We report newly observed VRI photometry for all 63 objects and new trigonometric parallaxes for 37 objects. The remaining 26 objects have trigonometric parallaxes from the literature. We combine our optical photometry and trigonometric parallaxes with 2MASS and WISE photometry and employ a novel spectral energy distribution fitting algorithm to determine effective temperatures, bolometric luminosities, and radii. Our uncertainties range from ~20K to ~150K in temperature, ~0.01 to ~0.06 in log (L/L_{sun}_) and ~3% to ~10% in radius. We check our methodology by comparing our calculated radii to radii directly measured via long baseline optical interferometry. We find evidence for the local minimum in the radius-temperature and radius-luminosity trends that signals the end of the stellar main sequence and the start of the brown dwarf sequence at T_eff_~2075K, log(L/L_{sun}_)~-3.9, and (R/R_{sun}_)~0.086. The existence of this local minimum is predicted by evolutionary models, but at temperatures ~400K cooler. The minimum radius happens near the locus of 2MASS J0523-1403, an L2.5 dwarf with V-K=9.42. We make qualitative arguments as to why the effects of the recent revision in solar abundances accounts for the discrepancy between our findings and the evolutionary models. We also report new color-absolute magnitude relations for optical and infrared colors which are useful for estimating photometric distances. We study the optical variability of all 63 targets and find an overall variability fraction of 36_-7_^+9^% at a threshold of 15mmag in the I band, which is in agreement with previous studies. Description: We obtained VRI photometry for all targets in our sample using the Cerro Tololo Inter-American Observatory (CTIO) 0.9m telescope for the brighter targets and the SOuthern Astrophysical Research (SOAR) Optical Imager camera on the SOAR 4.1m telescope for fainter targets. SOAR observations were conducted between 2009 September and 2010 December during six observing runs comprising NOAO programs 2009B-0425, 2010A-0185, and 2010B-0176. A total of 17 nights on SOAR were used for optical photometry. Table 1 shows the photometry in the photometric system used by the telescope with which the measurements were taken (Johnson-Kron-Cousins for the CTIO 0.9m telescope and Bessell for SOAR). Astrometric observations are based in part on observations obtained via the Cerro Tololo Inter-American Observatory Parallax Investigation (CTIOPI), at the Cerro Tololo 0.9m telescope. CTIOPI is a large and versatile astrometric monitoring program targeting diverse types of stellar and substellar objects in the solar neighborhood. Observations are taken using the CTIO 0.9m telescope and its sole instrument, a 2048*2048 Tektronix imaging CCD detector with a plate scale of 0.401''/pixel. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 276 63 Observed and derived properties table4.dat 146 37 New trigonometric parallaxes, proper motions, and optical variability notes.dat 1472 13 Notes refs.dat 62 35 References -------------------------------------------------------------------------------- See also: II/328 : AllWISE Data Release (Cutri+ 2013) II/311 : WISE All-Sky Data Release (Cutri+ 2012) II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003) http://wise2.ipac.caltech.edu/docs/release/allsky/ : WISE All Sky Catalog J/AJ/144/64 : Solar neighborhood. XXVIII. Substellar companions (Dieterich+, 2012) J/AJ/142/92 : New proper motion stars with pm>=0.18"/yr (Boyd+, 2011) J/AJ/142/10 : New proper motion stars 0.40"/yr>pm>=0.18"/yr (Boyd+, 2011) J/AJ/141/21 : CCD distance estimates of SCR targets (Winters+, 2011) J/AJ/134/252 : New nearby white dwarf systems (Subasavage+, 2007) J/AJ/133/2898 : New proper-motion stars (-90