Detalles de publicación
PP 017018
Primeval very low-mass stars and brown dwarfs - II. The most metal-poor substellar object
(1) Instituto de Astrofisica de Canarias, E-38205 La Laguna, Tenerife, Spain;
(2) Universidad de La Laguna, Dept. Astrofisica, E-38206 La Laguna, Tenerife, Spain;
(3) Zentrumfur Astronomie der Universitat Heidelberg, Landessternwarte Konigstuhl 12, D-69117 Heidelberg, Germany;
(4) Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB, UK;
(5) Univ Lyon, ENS de Lyon, Univ Lyon 1, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69007, Lyon, France;
(6) Main Astronomical Observatory, Academy of Sciences of the Ukraine, Golosiiv Woods, 03680 Kyiv-127, Ukraine.
SDSS J010448.46+153501.8 has previously been classified as an sdM9.5 subdwarf. However, it's very blue J-K colour (-0.15+/-0.17) suggests a much lower metallicity compared to normal sdM9.5 subdwarfs. Here we re-classify this object as a usdL1.5 subdwarf based on a new optical and near-infrared spectrum obtained with X-shooter on the Very Large Telescope. Spectral fitting with BT-Settl models leads to Teff = 2450+/-150 K, [Fe/H] = -2.4+/-0.2 and log g = 5.5+/-0.25. We estimate a mass for SDSS J010448.46+153501.8 of 0.0855+/-0.0015 M_Sun which is just below the hydrogen-burning minimum mass at [Fe/H] = -2.4 (~0.0875 M_Sun) according to evolutionary models. Our analysis thus shows SDSS J0104+15 to be the most metal-poor and highest mass substellar object known to date. We found that SDSS J010448.46+153501.8 is joined by another five known L subdwarfs (2MASS J05325346+8246465, 2MASS J06164006-6407194, SDSS J125637.16-022452.2, ULAS J151913.03-000030.0, and 2MASS J16262034+3925190) in a `halo brown dwarf transition zone' in the Teff-[Fe/H] plane, which represents a narrow mass range in which unsteady nuclear fusion occurs. This halo brown dwarf transition zone forms a `substellar subdwarf gap' for mid L to early T types.