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

Zhang, Z. H.;Pinfield, D. J.;Gálvez-Ortiz, M. C.;Burningham, B.;Lodieu, N.;Marocco, F.;Burgasser, A. J.;Day-Jones, A. C.;Allard, F.;Jones, H. R. A.;Homeier, D.;Gomes, J.;Smart, R. L. 2017. Primeval very low-mass stars and brown dwarfs – I. Six new L subdwarfs, classification and atmospheric properties. Monthly Notices of the Royal Astronomical Society 464, 3, 3040-3059, DOI: 10.1093/mnras/stw2438

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-typeMand 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.

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