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.

AbstracL W O new methods for madelling Kolmogomv phase fluctuations oyer a finite apenure are described. Ihe firs1 method relies on the incorporation of subharmonim in order to model accurately the low frequencies of the Kolmogomv SpeclNm. Ihc second method provides a less accurate, but much faster method for simulating the Kolmogorw spectrum ty using a midpoint displacement algorithm used in computer graphics. BackgroundThe simulation of atmospherically distorted wavefronts is an important tool for studying light propagation and imaging. The work in this paper is motivated by the need to develop efficient and effective methods of imaging astronomical objects through the turbulent atmosphere. Although the true test of any imaging algorithm is always provided by actual data, a good simulation is needed to be able to test different algorithms both in a controlled manner and under a wide variety of conditions. This paper outlines new methods for simulating the effects of static atmospheric turbulence, which is an essential component of any atmospheric imaging simulation.The starting point for nearly all analyses of atmospheric turbulence has been the assumption that atmospheric turbulence follows a Kolmogorov spectrum and has a phase that is statistically uniform Over the interval -T to T . The fluctuations induced by the turbulence then cause a distortion of both the magnitude and phase of the wavefront incident on the atmosphere. In practice the phase distortion has considerably more effect on the quality of images formed from light passing through the turbulence than those effects due to the magnitude distortion. In many situations, an adequate approximation is a single phase screen located at the entrance pupil of the optical system, although this can not account for non-isoplanatic effects [l].A typical short exposure image formed by viewing a point source through turbulence does not consist of a single diffraction pattern with a diameter fixed by the diffraction limit of the telescope, but rather the image consists of a number of superimposed speckles distributed over a diameter determined by the severity of the turbulence. Each individual bright speckle has a diameter given approximately by the diffraction limit of the telescope. It is important that in addition to the production of a speckled distortion of the image, the simulated turbulence should also shift the centroid of the image formed. This effect of centroid motion is primarily due to the low frequencies in the Kolmogorov spectrum, which are often not modelled well in conventional F F l procedures.Whilst it has been proposed that the centroid motion can be compensated after the generation of the speckles, this is not the only part of the information present

Abstract. We present the first long baseline mid-infrared interferometric observations of the circumstellar disks surrounding Herbig Ae/Be stars. The observations were obtained using the mid-infrared interferometric instrument MIDI at the European Southern Observatory (ESO) Very Large Telescope Interferometer VLTI on Cerro Paranal. The 102 m baseline given by the telescopes UT1 and UT3 was employed, which provides a maximum full spatial resolution of 20 milli-arcsec (mas) at a wavelength of 10 µm. The interferometric signal was spectrally dispersed at a resolution of 30, giving spectrally resolved visibility information from 8 µm to 13.5 µm. We observed seven nearby Herbig Ae/Be stars and resolved all objects. The warm dust disk of HD 100546 could even be resolved in single-telescope imaging. Characteristic dimensions of the emitting regions at 10 µm are found to be from 1 AU to 10 AU. The 10 µm sizes of our sample stars correlate with the slope of the 10-25 µm infrared spectrum in the sense that the reddest objects are the largest ones. Such a correlation would be consistent with a different geometry in terms of flaring or flat (self-shadowed) disks for sources with strong or moderate mid-infrared excess, respectively. We compare the observed spectrally resolved visibilities with predictions based on existing models of passive centrally irradiated hydrostatic disks made to fit the SEDs of the observed stars. We find broad qualitative agreement of the spectral shape of visibilities corresponding to these models with our observations. Quantitatively, there are discrepancies that show the need for a next step in modelling of circumstellar disks, satisfying both the spatial constraints such as are now available from the MIDI observations and the flux constraints from the SEDs in a consistent way.Key words. stars: circumstellar matter -techniques: interferometric -stars: formation -stars: pre-main-sequenceinfrared: stars Based on observations made with the Very Large Telescope Interferometer at Paranal Observatory.

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Abstract. We present near-IR speckle images of 21 massive Young Stellar Objects (YSOs) associated with outflows. The aim of this study is to search for sub-arcsecond reflection nebulae associated with the outflow cavity. We find that 6 of the massive YSOs show a conical nebula which can be interpreted in terms of reflected light from the dusty walls of the outflow cavity. In all cases, the small scale structures seen in our images are compared with outflow indicators found in the literature. No clear correlation is found between the presence of the reflection nebulosity and any property such as degree of embeddedness. We also note that 3 of the sources show close companions, one of them belonging also to the sample with conical nebula.