00 5 The First High - Resolution Spectra of 1 . 3 L Subdwarfs

Abstract

We present the first high-resolution (R ≈ 31 000) spectra of the cool sdL 2MASS0532+8246, and what was originally identified as an early-type L subdwarf (sdL) LSR 1610 – 0040. Our work, in combination with contemporaneous work by Cushing and Vacca, makes it clear that the latter object is more probably a mid-M dwarf with an unusual composition that gives it some sub-dwarf spectral features. We use the data to derive precise radial velocities for both objects and to estimate space motion; both are consistent with halo kinematics. We measure the projected rotational velocities, revealing very slow rotation for the old sd?M6 object LSR 1610 – 0040. 2MASS0532+8246 exhibits rapid rotation of v sin i = 65 ± 15 km s, consistent with the behavior of L dwarfs. This means that the braking time for L dwarfs is extremely long, or that perhaps they never slow down. A detailed comparison of the atomic Rb and Cs lines to spectra of field L dwarfs shows the spectral type 2MASS0532+8246 is consistent with being midto late-L. The Rb I and K I lines of LSR 1610 – 0040 are like an early-L dwarf, but the Cs I line is like a mid-M dwarf. The appearance of the Ca II triplet in absorption in this object is very hard to understand if it is not as least as warm as M6. We explain these effects in a consistent way using a mildly metal-poor midM model. M subdwarfs have weak metal-oxides and enhanced metal-hydrides relative to normal M dwarfs. LSR 1610 – 0040 exhibits metal-hydrides like an M dwarf but metal-oxides like a subdwarf. The same explanation that resolves the atomic line discrepancy explains this as well. Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, D-21029 Hamburg, Germany ⋆ Marie Curie Outgoing International Fellow

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Cite this paper

@inproceedings{Reiners2005005T, title={00 5 The First High - Resolution Spectra of 1 . 3 L Subdwarfs}, author={Ansgar Reiners and G . Basri}, year={2005} }