PMAS:: The Potsdam Multi-Aperture Spectrophotometer.: I.: Design, manufacture, and performance

We describe the design, manufacture, commissioning, and performance of PMAS, the Potsdam Multi-Aperture Spectrophotometer. PMAS is a dedicated integral field spectrophotometer optimized to cover the optical wavelength regime of 0.35 - 1 mu m. It is based on the lens array - fiber bundle principle of operation. The instrument employs an all-refractive fiber spectrograph, built with CaF2 optics, to provide good transmission and high image quality over the entire nominal wavelength range. A set of user-selectable reflective gratings provides low to medium spectral resolution of approximately 1.5, 3.2, and 7 angstrom in first order, depending on the groove density ( 1200, 600, 300 grooves mm(-1)). While the standard integral field unit (IFU) uses a element 16 x 16 lens array, which provides seeing-limited sampling in a relatively small field of view (FOV) in one of three magnifications (8 '' x 8 '', 12 '' x 12 '', or 16 '' x 16 ''), a recently retrofitted bare fiber bundle IFU (PPak: PMAS fiber pack) expands the FOV to a hexagonal area with a footprint of 65 '' x74 ''. Other special features include a cryogenic CCD camera for field acquisition and guiding, a nod-shuffle mode for beam switching and improved sky background subtraction, and a scanning Fabry-Perot etalon in combination with the standard IFU ( PYTHEAS mode). PMAS was initially designed and built as an experimental traveling instrument with optical interfaces to various telescopes (Calar Alto 3.5 m, ESO VLT, LBT). It is offered as a common-user instrument at Calar Alto under contract to MPIA Heidelberg since 2002.