• DOI:10.1093/mnras/stx350
• Corpus ID: 54847595

Primeval very low-mass stars and brown dwarfs -- II. The most metal-poor substellar object

@article{Zhang2017PrimevalVL,
  title={Primeval very low-mass stars and brown dwarfs -- II. The most metal-poor substellar object},
  author={Z H Zhang and Derek Homeier and David J. Pinfield and Nicolas Lodieu and Hugh R. A. Jones and France Allard and Ya. V. Pavlenko},
  journal={Monthly Notices of the Royal Astronomical Society},
  year={2017},
  volume={468},
  pages={261-271}
}

• Z. Zhang, D. Homeier, +4 authors Y. Pavlenko
• Published 7 February 2017
• Physics, Geology
• Monthly Notices of the Royal Astronomical Society

SDSS J010448.46+153501.8 has previously been classified as an sdM9.5 subdwarf. However, its very blue $J-K$ colour ($-0.15 \pm 0.17$) 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 $T_{\rm eff}$ = 2450 $\pm$ 150 K, [Fe/H] = $-$2.4 $\pm$ 0.2 and log $g$ = 5.5 $\pm$ 0.25. We estimate a mass for SDSS J010448.46+153501.8 of 0.086 $\pm$ 0.0015 M$_{\odot}$ which is just below the hydrogen-burning minimum mass at [Fe/H] = $-$2.4 ($\sim$0.088 M$_{\odot}$) according to evolutionary models. Our analysis thus shows SDSS J0104+15 to be the most metal-poor and highest mass substellar object known to-date. We found that SDSS J010448.46+153501.8 is joined by another five known L subdwarfs (2MASS J05325346+8246465, 2MASS J06164006$-$6407194, SDSS J125637.16$-$022452.2, ULAS J151913.03$-$000030.0 and 2MASS J16262034+3925190) in a 'halo brown dwarf transition zone' in the $T_{\rm eff}-$[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.