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 µm. It is based on the lens array -fiber bundle principle of operation. The instrument employs an all-refractive fiber spectrograph, built with CaF 2 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 in first order of approx. 1.5, 3.2, and 7 Å, depending on the groove density (1200, 600, 300 gr/mm). While the standard integral field unit (IFU) uses a 16×16 element lens array, which provides seeing-limited sampling in a relatively small field-of-view (FOV) in one of three magnifications (8×8, 12×12, or 16×16 arcsec 2 , respectively), a recently retrofitted bare fiber bundle IFU (PPak) expands the FOV to a hexagonal area with a footprint of 65×74 arcsec 2 . 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-Pérot 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 3.5m, ESO-VLT, LBT). It is offered as a common user instrument at Calar Alto under contract with MPIA Heidelberg since 2002.

The Multi Unit Spectroscopic Explorer (MUSE) is a second-generation VLT panoramic integral-field spectrograph currently in manufacturing, assembly and integration phase. MUSE has a field of 1x1 arcmin² sampled at 0.2x0.2 arcsec² and is assisted by the VLT ground layer adaptive optics ESO facility using four laser guide stars. The instrument is a large assembly of 24 identical high performance integral field units, each one composed of an advanced image slicer, a spectrograph and a 4kx4k detector. In this paper we review the progress of the manufacturing and report the performance achieved with the first integral field unit.

In pixel-level image sequence fusion, a composite image sequence has to be built of several spatially registered input image sequences. One of the primary goals in image sequence fusion is the temporal stability and consistency of the fused image sequence. To fulfill the preceding desiderata, we propose a novel approach based on a shift invariant extension of the 2D discrete wavelet transform, which yields an overcomplete and thus shift invariant multiresolution signal representation. The advantage of the shift invariant fusion method is the improved temporal stability and consistency of the fused sequence, compared to other multiresolution fusion methods. To evaluate temporal stability and consistency of the fused sequence we introduce a quality measure based on the mutual information between the inter-frame-differences (IFD) of the input sequences and the fused image sequence. If the mutual information is high, the information in the IFD of the fused sequence is low with respect to the information present in the IFDs of the input sequences, indicating a stable and consistent fused image sequence. We evaluate the performance of several multiresolution fusion schemes on a real word image sequence pair and show that the shift invariant fusion method outperforms the other multiresolution fusion methods with respect to temporal stability and consistency.

PEPSI is the bench-mounted, two-arm, fibre-fed and stabilized Potsdam Echelle Polarimetric and Spectroscopic Instrument for the 2×8.4 m Large Binocular Telescope (LBT). Three spectral resolutions of either 43 000, 120 000 or 270 000 can cover the entire optical/red wavelength range from 383 to 907 nm in three exposures. Two 10.3k×10.3k CCDs with 9-μm pixels and peak quantum efficiencies of 94-96 % record a total of 92échelle orders. We introduce a new variant of a wave-guide image slicer with 3, 5, and 7 slices and peak efficiencies between 92-96 %. A total of six cross dispersers cover the six wavelength settings of the spectrograph, two of them always simultaneously. These are made of a VPH-grating sandwiched by two prisms. The peak efficiency of the system, including the telescope, is 15 % at 650 nm, and still 11 % and 10 % at 390 nm and 900 nm, respectively. In combination with the 110 m 2 light-collecting capability of the LBT, we expect a limiting magnitude of ≈ 20th mag in V in the low-resolution mode. The R = 120 000 mode can also be used with two, dual-beam Stokes IQUV polarimeters. The 270 000-mode is made possible with the 7-slice image slicer and a 100-μm fibre through a projected sky aperture of 0.74 , comparable to the median seeing of the LBT site. The 43 000-mode with 12-pixel sampling per resolution element is our bad seeing or faint-object mode. Any of the three resolution modes can either be used with sky fibers for simultaneous sky exposures or with light from a stabilized Fabry-Pérotétalon for ultra-precise radial velocities. CCD-image processing is performed with the dedicated data-reduction and analysis package PEPSI-S4S. Its full error propagation through all image-processing steps allows an adaptive selection of parameters by using statistical inferences and robust estimators. A solar feed makes use of PEPSI during day time and a 500-m feed from the 1.8 m VATT can be used when the LBT is busy otherwise. In this paper, we present the basic instrument design, its realization, and its characteristics. Some pre-commissioning first-light spectra shall demonstrate the basic functionality.

Abstract. STELLA is a robotic observatory with two fully automatic telescopes (STELLA-I and STELLA-II) located at the Teide Observatory in Tenerife, Spain. Not only the telescopes are automatic but also the entire observatory, no human presence is needed for observing -not even in remote control. STELLA-I supports a high-resolution, fiber-fed and benchmounted echelle spectrograph and a wide-field CCD imaging photometer while STELLA-II feeds a similar but wide-band imaging photometer and a testbed for prototype adaptive optics for robotic telescopes. The first telescope is scheduled for first light in