Quality of stellar radial velocities improved in DR6

The wavelength calibration of the SDSS spectra is problematic in the blue, because of a dearth of strong lines in the calibration lamps and in the nighttime sky. This led to systematic errors at the level of 10-15 km/s (i.e., 0.15-0.25 pixels) in the wavelength calibration at the extreme blue end, which was affecting both stellar model fits and the determination of radial velocities. More robust fitting algorithms brought these problems under control in DR6 and beyond.

The identity of the actual template stars are tabulated below. The 'Template Number' corresponding to the highest cross correlation peak match for any spectrum may be found under the keyword 'BESTTEMP' in the PDU header of a SDSS spSpec-$mjd-$plate-$fiberid.fit file.