Primeval very low-mass stars and brown dwarfs - III. The halo transitional brown dwarfs

Z. H. Zhang, D. J. Pinfield, M. C. Galvez-Ortiz, D. Homeier, A. J. Burgasser, N. Lodieu, E. L. Martin, M. R. Zapatero Osorio, F. Allard, H. R. A. Jones, R. L. Smart, B. Lopez Marti, B. Burningham, R. Rebolo

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)
57 Downloads (Pure)


We report the discovery of an esdL3 subdwarf, ULAS J020858.62+020657.0 and a usdL4.5 subdwarf, ULAS J230711.01+014447.1. They were identified as L subdwarfs by optical spectra obtained with the Gran Telescopio Canarias, and followed up by optical to near infrared spectroscopy with the Very Large Telescope. We also obtained an optical to near infrared spectrum of a previously known L subdwarf, ULAS J135058.85+081506.8, and re-classified it as a usdL3 subdwarf. These three objects all have typical halo kinematics. They have $T_{\rm eff}$ around 2050-2250 K, $-$1.8 $\leq$ [Fe/H] $\leq -$1.5, and mass around 0.0822-0.0833 M$_{\odot}$, according to model spectral fitting and evolutionary models. These sources are likely halo transitional brown dwarfs with unsteady hydrogen fusions, as their masses are just below the hydrogen-burning minimum mass, which is $\sim$ 0.0845 M$_{\odot}$ at [Fe/H] = $-$1.6 and $\sim$ 0.0855 M$_{\odot}$ at [Fe/H] = $-$1.8. Including these, there are now nine objects in the `halo brown dwarf transition zone', which is a `substellar subdwarf gap' spans a wide temperature range within a narrow mass range of the substellar population.
Original languageEnglish
Pages (from-to)1383–1391
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date23 May 2018
Publication statusPublished - 1 Sept 2018


  • astro-ph.SR


Dive into the research topics of 'Primeval very low-mass stars and brown dwarfs - III. The halo transitional brown dwarfs'. Together they form a unique fingerprint.

Cite this