The First High-Resolution Spectra of 1.3 L Subdwarfs

We present the first high-resolution (R ~ 31,000) spectra of the cool sdL2MASS0532, and what was originally identified as an early-type L subdwarf (sdL)LSR1610-0040. Our work, in combination with contemporaneous work by Cushing andVacca, makes it clear that the latter object is more probably a mid-M dwarfwith an unusual composition that gives it some sub-dwarf spectral features. Weuse the data to derive precise radial velocities for both objects and toestimate space motion; both are consistent with halo kinematics. We measure theprojected rotational velocities, revealing very slow rotation for the old sd?M6object \lsr. \twom exhibits rapid rotation of vsini = 65 +- 15km/s, consistentwith the behavior of L dwarfs. This means that the braking time for L dwarfs isextremely long, or that perhaps they never slow down. A detailed comparison ofthe atomic Rb and Cs lines to spectra of field L dwarfs shows the spectral type\twom is consistent with being mid- to late-L. The Rb I and K I lines of \lsr\are like an early-L dwarf, but the Cs I line is like a mid-M dwarf. Theappearance of the Ca II triplet in absorption in this object is very hard tounderstand if it is not as least as warm as M6. We explain these effects in aconsistent way using a mildly metal-poor mid-M model. M subdwarfs have weakmetal-oxides and enhanced metal-hydrides relative to normal M dwarfs. \lsr\exhibits metal-hydrides like an M dwarf but metal-oxides like a subdwarf. Thesame explanation that resolves the atomic line discrepancy explains this aswell. We identify atomic lines of Ti around 9600 \AA and a small contributionof FeH, but we cannot confirm a detection of TiH in the spectra of cool Lsubdwarfs. High resolution spectroscopy has aided in beginning to understandthe complex molecular chemistry in metal-deficient and ultralow-mass objects.Comment: accepted for publication in the Astronomical Journal, abstract shortene