Segmented zero-deviation cross-dispersion prisms for the Hectochelle multiobject spectrograph

We present a design for a zero-deviation cross-disperser to be used with Hectochelle, a fiber-fed echelle spectrograph. Hectochelle was originally designed to be operated as a multiobject spectrograph in a single order (or overlapping orders) selected with order-separating filters. With cross-dispersion, the multiplex advantage can be traded for spectral coverage using order-separating filters and masks at the fiber slit. The options range from using two fibers delivering the full 365-980 nm passband to 240 fibers delivering a single order (10-20 nm). The cross-disperser is a novel segmented prism design, which is compact, efficient, and economical compared to a monolithic zero-deviation prism. Conveniently, the cross-disperser can be mounted in the existing Hectochelle spectrograph without mechanical modifications or optical realignment.