Primeval very low-mass stars and brown dwarfs - I. Six new L subdwarfs, classification and atmospheric properties

Z. H. Zhang , D. J. Pinfield , M. C. Gálvez-Ortiz , B. Burningham , N. Lodieu , F. Marocco , A. J. Burgasser , A. C. Day-Jones , F. Allard (1) , H. R. A. Jones , D. Homeier , J. Gomes , R. L. Smart

1 CRAL - Centre de Recherche Astrophysique de Lyon

We have conducted a search for L subdwarf candidates within the photometric catalogues of the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky Survey. Six of our candidates are confirmed as L subdwarfs spectroscopically at optical and/or near-infrared wavelengths. We also present new optical spectra of three previously known L subdwarfs (WISEA J001450.17-083823.4, 2MASS J00412179+3547133, and ULAS J124425.75+102439.3). We examined the spectral type and metallicity classification of subclasses of known L subdwarfs. We summarized the spectroscopic properties of L subdwarfs with different spectral types and subclasses. We classify these new L subdwarfs by comparing their spectra to known L subdwarfs and L dwarf standards. We estimate temperatures and metallicities of 22 late-type M and L subdwarfs by comparing their spectra to BT-Settl models. We find that L subdwarfs have temperatures between 1500 and 2700 K, which are higher than similar-typed L dwarfs by around 100-400 K depending on different subclasses and subtypes. We constrained the metallicity ranges of subclasses of M, L, and T subdwarfs. We also discussed the spectral-type and absolute magnitude relationships for L and T subdwarfs.

Mots clés: brown dwarfs; stars: chemically peculiar; stars: individual: ULAS J021642.97+004005.6; ULAS J124947.04+095019.8; SDSS J133348.24+273508.8; ULAS J133836.97-022910.7; SDSS J134749.74+333601.7; ULAS J151913.03-000030.0; stars: low-mass; stars: Population II; subdwarfs; Astrophysics - Solar and Stellar Astrophysics

Domaines: Planète et Univers [physics]; Astrophysique [astro-ph]

Z. H. Zhang, D. J. Pinfield, M. C. Gálvez-Ortiz, B. Burningham, N. Lodieu, et al.. Primeval very low-mass stars and brown dwarfs - I. Six new L subdwarfs, classification and atmospheric properties. Monthly Notices of the Royal Astronomical Society, 2017, 464, pp.3040-3059. ⟨10.1093/mnras/stw2438⟩. ⟨insu-03710632⟩