Removal of Telluric Features

Telluric corrections are carried out as follows. Note that this is done prior to radial velocity corrections because telluric features are fixed in the observed frame of reference. For each program star a suitable telluric observation (same night observation of a star from a list of telluric names) is selected; these telluric ``standards'' are rapidly rotating B stars. The telluric star is continuum normalized with a cubic spline of 5 pieces fit to non-telluric regions, where the telluric regions to be scaled and removed are specified in Table~\ref{telluric}. After the continuum fitting, the non-telluric regions are set to 1 so that that those regions do not modify the matching regions in the program star. The telluric features are removed by scaling and dividing the template telluric regions into the stellar data. The scaling and any small wavelength shift are determined by minimization of the root mean square in the corrected spectra over the telluric regions. Hence, in effect, the telluric regions in the telluric stars are continuum normalized from nearby regions and only those regions are used to correct the program stars. For the program stars, data outside the telluric regions is not modified by this procedure.