pseudo-equivalent widths (pEWs). Spectral features were deblended using the IRAF task [splot]{} and the pEWs derived by fitting Voigt functions to the deblended lines.

Results
=======

K band Spectra
--------------

The extracted 1D spectra of nine brown dwarf calibrators are shown in Figure 1. All spectra were smoothed using three pixel boxcars.

                                 Age (Myr)     pEW NaI (Å)     pEW CaI (Å)      pEW CO (Å)
  ----------------------------- ------------ --------------- --------------- ----------------
          2MASS 0345+25          $\geq$1000   4.1$\pm$ 0.2    1.1$\pm$ 0.1    15.1$\pm$ 0.2
         BRI 0021$-$0214         $\geq$1000   2.2$\pm$ 0.1    1.3$\pm$ 0.1    18.8$\pm$ 0.1
       $\sigma$ Orionis 51          3-7       1.0$\pm$ 0.5    0.5$\pm$ 0.3     9.3$\pm$ 0.6
       $\sigma$ Orionis 71          3-7       1.8$\pm$ 0.5         $-$         8.4$\pm$ 0.5
   $\sigma$ Orionis J053$-$024      3-7       2.1$\pm$ 0.6         $-$         9.4$\pm$ 0.5
           KPNO-Tau 1               1-2       1.8$\pm$ 0.2    0.3$\pm$ 0.1    12.4$\pm$ 0.2
           KPNO-Tau 4               1-2       1.0$\pm$ 0.1    0.6$\pm$ 0.1    10.3$\pm$ 0.1
           KPNO-Tau 12              1-2       1.2$\pm$ 0.3         $-$         9.8$\pm$ 0.2
        2MASS 0535$-$0546           1-2       1.1$\pm$ 0.1    0.9$\pm$ 0.1    10.4$\pm$ 0.1
           0457$+$3015              1-2       1.7 $\pm$ 0.3   0.9 $\pm$ 0.1   10.5 $\pm$ 0.2
             \[1ex\]                                                         

\[tab:2\]

                                 Rotational Velocity (v sin i) kms$^{-1}$  
  ----------------------------- ------------------------------------------ --
          2MASS 0345+25                          25$^{1}$                  
         BRI 0021$-$0214                         40$^{2}$                  
       $\sigma$ Orionis 51                         $-$                     
       $\sigma$ Orionis 71                         $-$                     
   $\sigma$ Orionis J053$-$024                     $-$                     
           KPNO-Tau 1                           5.5$^{3}$                  
           KPNO-Tau 4                            10$^{3}$                  
           KPNO-Tau 12                           5$^{3}$                   
        2MASS 0535$-$0546                        