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

Zhang, Z. H., Pinfield, D. J., Galvez-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. and 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 (MNRAS), 464 (3). pp. 3040-3059. ISSN 0035-8711
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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, ULAS J124425.75+102439.3). We examined the spectral types and metallicity subclasses classification of known L subdwarfs. We summarised 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 K and 2700 K, which are higher than similarly-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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