estimate radial velocity at fixed metallicity

We use the best-fit model template from the broad-band fit when we measure the radial velocity of a FLUXSTD. However, the broad-band photometry is insensitive to metallicity and [Fe/H] is virtually left unconstrained. Absorption lines depths are of course dependent on metallicity, and we want to use metallicity that is close to that of the FLUXSTD. The subsequent spectral fitting (which is sensitive to metallicity) often finds [Fe/H] ~ -1. Adopt this metallicity when we estimate the radial velocity and see if there is any improvement.