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

Z. H. Zhang, D. Homeier, David Pinfield, N. Lodieu, Hugh Jones, F. Allard, Ya V. Pavlenko

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21 Citations (Scopus)
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Abstract

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 (\sim0.0875 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.
Original languageEnglish
Pages (from-to)261-271
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Volume468
Issue number1
Early online date22 Feb 2017
DOIs
Publication statusPublished - 1 Jun 2017

Keywords

  • brown dwarfs
  • stars: chemically peculiar
  • stars: individual: SDSS J010448 + 153501.8
  • stars: low-mass
  • stars: Population II
  • subdwars

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