The Multi Unit Spectroscopic Explorer (MUSE) is an integral field spectrograph on the Very Large Telescope Unit Telescope 4. The MUSE adaptive optics observing capabilities include a wide field (1 square arcmin), ground layer seeing-enhanced AO mode (WFM-AO), and a narrow field (7.5”×7.5”), laser tomography AO mode (NFM-AO). The MUSE AO observations use four laser guide stars (4LGS) to correct the atmospheric turbulence. The MUSE AO observations routinely improve image quality by a factor of 2 in the seeing-enhanced wide field (WFM-AO) observations and deliver image quality down to 50-60 milliarcsecond (mas) in the laser tomography AO (NFM-AO) mode. The 4LGS and AO systems at UT4 are stable, but there is still some chance that one of the lasers or Wavefront Sensors (WFS) is out of service, leaving us with 3LGS. In the last few years, we have successfully commissioned and characterized the MUSE AO degraded mode (3LGS mode) for both MUSE WFM-AO and NFM-AO modes. In this paper, we present the commissioning activities, the procedure developed to switch between 4LGS and 3LGS mode, and the performance characterization of the MUSE-NFM AO degraded mode.
The Multi Unit Spectroscopic Explorer (MUSE) is an integral field spectrograph on the Very Large Telescope Unit Telescope 4, capable of laser guide star assisted and tomographic adaptive optics using the GALACSI module. Its observing capabilities include a wide field (1 square arcmin), ground layer AO mode (WFM-AO) and a narrow field (7.5”×7.5”), laser tomography AO mode (NFM-AO). The latter has had several upgrades in the 4 years since commissioning, including an optimization of the control matrices for the AO system and a new sub-electron noise detector for its infra-red low order wavefront sensor. We set out to quantify the NFM-AO system performance by analysing ∼230 spectrophotometric standard star observations taken over the last 3 years. To this end we expand upon previous work, designed to facilitate analysis of the WFM-AO system performance. We briefly describe the framework that will provide a user friendly, semi-automated way for system performance monitoring during science operations. We provide the results of our performance analysis, chiefly through the measured Strehl ratio and full width at half maximum (FWHM) of the core of the point spread function (PSF) using two PSF models, and correlations with atmospheric conditions. These results will feed into a range of applications, including providing a more accurate prediction of the system performance as implemented in the exposure time calculator, and the associated optimization of the scientific output for a given set of limiting atmospheric conditions.
The Multi-Unit Spectroscopic Explorer instrument (MUSE), is an integral-field spectrograph at one of the Nasmyth foci of the 8m-class Yepun telescope at Paranal observatory. MUSE's most powerful modes use the Adaptive Optics Facility consisting of a Deformable Secondary Mirror with over 1000 actuators commanded by a real-time computer up to 1000 times per second. At the core of the system are 4 laser guide stars monitored by GALACSI, the wave-front sensor system. MUSE functions with two modes: Wide-Field Mode (1'x1' field), making use of Ground Layer Adaptive Optics and Narrow-Field Mode (7.5"x7.5" field) using full laser tomography. In this work, we will present the results of a campaign to monitor the AO performance as measured by MUSE during the first years of operations. We will evaluate the dependence of this performance, as characterized by the point-spread function, on easily monitored environmental parameters such as ground-layer fraction, coherence time, seeing, and airmass.
The high multiplex advantage of VIMOS, the VLT visible imager and multi-object/integral-field spectrometer, makes it
a powerful instrument for large-scale spectroscopic surveys of faint sources. Following community input and
recommendations by ESO's Science and Technology Committee, in 2009 it was decided to upgrade the instrument. This
included installing an active flexure compensation system and replacing the detectors with CCDs that have a far better
red sensitivity and less fringing. Significant changes have also been made to the hardware, maintenance and operational
procedures of the instrument with the aim of improving availability and productivity. Improvements have also been
made to the data reduction pipeline. The upgrade will end in 2012 and the results of the program will be presented here.
HAWK-I is the newly commissioned High Acuity Wide-field K-band Imager at the ESO Very Large Telescope. It is a
0.9-2.5 micron imager with a field of view of 7.5×7.5 arcmin sampled at 106 mas with four Hawaii2RG detectors. It has
a full reflective design that was optimised for image quality and throughput.We present an overview of its performance as
measured during the commissioning and first science runs. In particular, we describe a detector read-out mode that allows
us to increase the useful dynamic range of the detector, and a distortion calibration resulting in <5mas relative astrometry
across the field.
We discuss the challenges to photometry introduced by internal redistribution of light in wide-field imaging cameras with focal-reducers. We have developed a simple least-squares procedure which can be used to determine the zero-point variations across the field. The method uses three orthogonally offseted images of a reasonably dense stellar field, plus an image containing at least three standard stars scattered across the field. The method, which does not require rotating the instrument, have been applied to correct data from the Wide Field Imager at La Silla. It has been shown to reduce a 12% center-to-edge gradient down to a ~2% rms variation accross the field. A new method which can be used with data taken during non-photometric nights is also presented.
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