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

Zhang, Z. H.Z. H.ZhangPinfield, D. J.D. J.PinfieldGálvez-Ortiz, M. C.M. C.Gálvez-OrtizHomeier, D.D.HomeierBurgasser, A. J.A. J.BurgasserLodieu, N.N.LodieuMartín, E. L.E. L.MartínZapatero Osorio, M. R.M. R.Zapatero OsorioAllard, F.F.AllardJones, H. R. A.H. R. A.JonesSMART, Richard LaurenceRichard LaurenceSMARTLópez Martí, B.B.López MartíBurningham, B.B.BurninghamRebolo, R.R.Rebolo2021-01-122021-01-1220180035-8711http://hdl.handle.net/20.500.12386/29678We 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 reclassified it as a usdL3 subdwarf. These three objects all have typical halo kinematics. They have Teff around 2050-2250 K, -1.8 ≤ [Fe/H] ≤ -1.5, and mass around 0.0822-0.0833 M☉, according to model spectral fitting and evolutionary models. These sources are likely halo transitional brown dwarfs with unsteady hydrogen fusion, as their masses are just below the hydrogen-burning minimum mass, which is ∼ 0.0845 M☉ at [Fe/H] = -1.6 and ∼ 0.0855 M☉ 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' that spans a wide temperature range within a narrow mass range of the substellar population.STAMPAenPrimeval very low-mass stars and brown dwarfs - III. The halo transitional brown dwarfsArticle10.1093/mnras/sty13522-s2.0-85055343067000441295800100https://academic.oup.com/mnras/article-abstract/479/1/1383/50018852018MNRAS.479.1383ZFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_6 Stars and stellar systems