10$^{4}$                  
            0457+3015                              $-$                     
   \[1ex\] $^{1}$ @antonova08                                              
         $^{2}$ @reid99                                                    
        $^{3}$ @mohanty05                                                  
        $^{4}$ @reiners07                                                  

\[tab:3\]

Equivalent Widths
-----------------

pEWs of the NaI doublet (2.206$\mu$m and 2.209$\mu$m) and of the CO band head starting at 2.294$\mu$m were obtained for all brown dwarf calibrators. pEWs of the CaI triplet (2.261$\mu$m, 2.263$\mu$m and 2.265$\mu$m) were obtained for both field dwarfs, one 3-7 Myr old object, and four 1-2 Myr old objects. These results are shown in Table 2. Table 3 shows, where known, the rotational velocities of the calibrators (obtained from the literature). Figure 2 shows the pEWs and their associated uncertainties. For comparison, Figure 2 also shows the NaI EWs of a sample of field dwarfs, M8 $\rightarrow$ M9.5, from the IRTF Spectral Library, contained in @cushing05 \[C05\] and @rayner09 \[R09\].

The pEW uncertainties in our sample of calibrator brown dwarfs were determined from the objects’ dispersed 2D images. The image (before sky subtraction) was used to compute the total number of photons over the region containing the absorption feature. The width of this region was determined from the NIFS instrument profile and was found to be $\sim$2.2040$\mu$m - 2.2095$\mu$m for all our objects. The sky-subtracted 2D image of this region was used to 