We present the first high-resolution ( R \approx 31 000 ) spectra of the cool sdL 2MASS 0532+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 .
2MASS 0532+8246 exhibits rapid rotation of v \sin { i } = 65 \pm 15 km s ^ { -1 } , 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 2MASS 0532+8246 is consistent with being mid- to 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 mid-M 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 .

Our spectra cover the spectral region around a previously unidentified absorption feature at 9600 Å , and the region around 9400 Å where detection of TiH has been claimed .
We identify the absorption around 9600 Å as due to atomic lines of Ti and a small contribution of FeH , but we can not confirm a detection of TiH in the spectra of cool L subdwarfs .
In 2MASS 0532+8246 , both metal-oxides and metal-hydrides are extremely strong relative to normal L dwarfs .
It may be possible to explain the strong oxide features in 2MASS 0532+8246 by invoking effects due to inhibited dust formation .
High resolution spectroscopy has aided in beginning to understand the complex molecular chemistry and spectral formation in metal-deficient and ultracool atmospheres , and the properties of early ultralow-mass objects .