A low-dispersion survey spectrograph (LDSS-2) for the William Herschel Telescope

LDSS-2 is a wide-field, multiaperture spectrograph recently installed on the 4.2-m William Herschel Telescope (WHT) in La Palma. The spectrograph has high system throughput (including the telescope and atmosphere) of similar to 20% at blaze. The field of view is 11.5 arcmin, allowing it to produce spectra of several tens of objects simultaneously at spectral resolutions up to R = 1000. The multiaperture masks are of exceptional quality and can be designed and manufactured rapidly at the telescope to improve target-mask registration and observational flexibility. This paper describes the instrument, the mask manufacturing facility, and the observing procedures required to acquire the target fields. Finally it presents examples of data obtained during the first commissioning run.