Due to the relatively small wavelength coverage, arc lines available for wavelength calibration are scarce and had to be complemented by atmospheric lines. The wavelength calibration for spectra taken at the same central wavelength during one night is not seen to change significantly.
Five lines were used to wavelength calibrate at Pa Beta: one Argon arc line
(1.28062 
) and four OH
emission lines (1.28065 
,
1.28248 
, 1.28346 
and 1.28450 
); three lines at Br Gamma: one Argon arc line
(2.16756 
) and two
telluric water absorption lines (2.163477 
and 2.168687 
).
The identification of the atmospheric lines was made with the help of Maihara et al. maihara93 for the OH lines and with the HITRAN database [Rothman et al. 1992] for the water lines. The wavelengths of the lines above are all vacuum wavelengths and were also obtained from these references.
The pairs (pixel number,wavelength) were fitted in both cases by a straight line using a least squares method (implemented in IDL). The best fit was then copied to the dispersion axis of all the relevant observation frames. The root mean square of the residuals of the fit (rms) is the uncertainty in the wavelength calibration and it is shown in velocity units in Table 3.1.
