Important recent changes (since Periods 93 and 94) regarding Paranal instrumentation and facilities

This section describes important changes which took place during Period 93 and 94, as well as changes expected to take place during Period 95.

UT instruments and facilities

Telescopes: all UTs

The concept of "Virtual Image Slicer" has been developed and implemented on the UTs. The Virtual Image Slicer consists in elongating the stars in a given direction by the introduction of a small amount of astigmatism thanks to the Active Optics of the telescope. Alignment of the major axis of the elongated star along the entrance slit of a spectrograph allows to increase the total signal collected in a single spectrum by a factor of up to 100 relative to a perfectly shaped image for bright sources in comparable execution time,  as overheads would otherwise be much longer than the actual observing (shutter) time. The use of the "Virtual Image Slicer" is only allowed in Visitor Mode  and is currently limited for use at the Cassegrain focus. It must be explicitly mentioned in box 8b 'Observing Mode Justification'. Details can be found in Guisard, Sterzik & Munoz Proc. SPIE 9145, Ground-based and Airborne Telescopes V, 914544 (July 22, 2014).

UT1 - Antu

  • CRIRES was taken out of operations as of July 17th, 2014 to undergo a major upgrade to transform it into a cross-dispersed echelle spectrograph. It is therefore not offered in Period 95. It is expected to be back in operations in 2017.
  • Instead, NACO has been offered on the Nasmyth A focus since Period 94, pending successfull commissioning, with a limited list of offered modes.
    • NAOS:
      • VIS & IR wavefront sensing
      • Pupil tracking
    • CONICA:
      • Imaging without chopping, including APP and NoAO; usage of the Mp filter is only possible in VM
      • Cube mode
      • Focal plane AGPM coronography, only in VM
      • Wollaston/HWP polarimetry, only in VM
      • Spectroscopy, only in VM
      • SAM/SAMPOL, only in VM.
    • The following modes are not offered: LGS, SDI+, 4QPM/Lyot coronography, APP spectroscopy.
    • The re-installation and commissioning of NACO on the UT1 Nasmyth A focus is planned to be completed by early September 2014: users are warned that this move has a non-negligible risk of failure.
  • FORS2: The anti-refllective coating of prisms which are part of the Longitudinal Atmospheric Dispersion Corrector (LADC) in front of the instrument is damaged and  therefore susceptible to introduce transmission loss larger than for uncoated prisms, variable transmission depending on the exact location of the beams crossing the prisms, scattering leading to a decreased signal-to-noise ratio on photometric measurements and variability of the transmission dependent on the humidity level.  During the M1 coating activities in November 2014, these prisms will be replaced by the ones which used to be in the LADC in front of FORS1 and for which the coating has been removed. Assessment of this exchange on the reachable limiting magnitudes as well as the achievable accuracy on differential photometry will be carried out immediately once the instrument is back on sky.  A decision will then be taken regarding the scientifically most interesting option compatible with the long term maintenance of the LADC.
  • KMOS
    • The arm allocation tool KARMA now offers the possibility to exclude individual arms from the arm configuration. Please consult the KMOS news page to confirm which arm is not available for which period.
    • A month-long intervention to improve the reliability of the arms will take place early in February 2015.

UT2 - Kueyen

    • XSHOOTER has been offered back on the Cassegrain focus of UT2 since Period 94.
    • The Atmospheric Dispersion Correction (ADC) systems on the UVB/VIS arms are not reliable. Since August 1st, 2012, the ADCs have been fixed in their non-deviant position. Data obtained in this configuration can be reduced by the pipeline without significant degradation. Updates on the status of the ADCs can be found on the XSHOOTER news webpage. The latest version of the user manual provides plots for helping users prepare observations without ADCs. Users are recommended to carry out observations at the parallactic angle whenever possible or to take special care on the airmass constraint to avoid flux loss. XSHOOTER will likely be taken out of operations for several months to install re-designed ADC systems in the future. As a consequence, Large and Monitoring Programmes using XSHOOTER will not be accepted in Period 95.
    • As of Period 93, XSHOOTER offers a new imaging mode using the Acquisition and Guiding camera. In combination with slit or IFU observations, this mode allows the users to take images of their object in various bands. However, in parallel, only the last snapshot of the acquisition sequence per se - i.e, in the acquisition template - is saved instead of a snapshot at each offset as it used to be done. More details can be found in the XSHOOTER User Manual and in the XSHOOTER News web pages.
  • FLAMES: Improved measures of the instrument efficiency at all settings have been acquired and are used to feed the latest version of the ETC (Version 5.1.0 -- May 20, 2014). As a result, the current ETC outputs a signal-to-noise ratio that can be significantly different from the output obtained using previous versions under the same conditions. The current ETC is expected to provide more accurate predictions of the signal-to-noise ratio. Compared to the previous ETC version, the predicted signal-to-noise ratios are generally lower in blue settings and higher in red settings. Significant differences (less than a factor 2) are expected in the most blue and most red settings.

UT3 - Melipal

  • SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) is an extreme adaptive optics system and coronagraphic facility. The primary science goal of this second generation VLT instrument is imaging, low-resolution spectroscopic, and polarimetric characterization of extra-solar planetary systems. The instrument design is optimized to provide the highest image quality and contrast performance in a narrow field of view around bright targets in the visible or near infrared bands. SPHERE is installed at the Nasmyth focus of UT3 and includes:
    • the Common Path and Infrastructure (CPI), which receives direct light from the telescope, and provides highly stabilized, AO-corrected, and coronagraphic beams to the three science instruments;
    • the Infrared Dual-Band Imager and Spectrograph (IRDIS), which provides Classical Imaging (CI), Dual-Band Imaging (DBI), Dual-Polarization Imaging (DPI), and Long Slit Spectroscopy (LSS) in low-resolution covering the range 0.95 to 2.32 μm with resolving power of R ~ 50 (LRS) or medium-resolution 0.95 to 1.65 μm with R ~ 400 (MRS);
    • the Integral Field Spectrograph (IFS), which provides a data cube of 38 monochromatic images either covering the range 0.95 to 1.35 μm (Y-J) at spectral resolution of R ~ 50 or 0.95 to 1.65 μm (Y-H) at R ~ 30, and
    • the Zurich IMaging POLarimeter (ZIMPOL), which provides diffraction limited classical imaging and differential polarimetric imaging (DPI) at 15 milli-arcsec resolution in the visible.
    SPHERE is offered for the first time in Period 95 pending successful commissioning and for a limited set of modes and setups. In particular, the IRDIS-DPI mode is not offered in Period 95.
  • VISIR is offered again in Period 95 pending successful re-commissioning taking place during Period 94 and in service mode only. The offered modes only include imaging and low- and long slit or cross-dispersed high-resolution spectroscopy. Sensitivities are the same as for the DRS detectors.
  • VIMOS:
    • For the MOS mode, analysis is currently ongoing to compare the accuracy of the attached nighttime calibrations with those taken during daytime. For Period 95, attached calibrations are still mandatory.
      Before the start of Phase 2, a report will be made available on the VIMOS web pages  in which the typical variation between day- and night-time calibration solutions, normalised to the resolution of the various grisms is quantified. Users will then be able to compare this information against their scientific requirements, and can request at Phase 2 to skip attached calibrations if appropriate.
    • Large and Monitoring Programmes are offered again in Period 95 subject to the following restriction: they cannot request dark or grey time at right ascensions between 02 and 03 h and/or dark time at about 10h, as these have been blocked by the VIMOS Public Spectroscopic Surveys.
    • Pre-imaging data taken before June 2011 is not valid any more for mask creation.
    • From Period 95 onwards, pre-imaging OBs are not allowed to be in concatenation containers. The execution time for pre-imaging runs has to be calculated for single OBs.
  • ISAAC was decommissioned in December 2013 and is no longer offered.

UT4 - Yepun

  • HAWK-I has been offered again on the Nasmyth A since Period 94.
    • Fast photometry has been offered both in Visitor and Service mode since Period 94. The burst mode is not offered any more since Period 94.
    • The filter NB1190 has replaced back the visitor filter NB0984.
    • The detector persistence limits have been revised.
    • Since Period 93, a new Pupil Tracking mode has been offered with NGS in both visitor and service modes. It allows to provide Angular Differential Imaging (ADI), in wavelength slices. An estimated 8 mag contrast (at 5 σ significance) is achievable at distances 3 to 5 λ/D (~ 0.17" to 0.43") from the primary star. However potential users should pay special attention to the restrictions listed in the section 2.9 of the User Manual, especially on the placement of the primary star as well as the flux limit. See the User Manual for details.
    • In June 2014, the grating wheel speeds have been lowered. A grating change between the 2 most separated gratings (J and H+K) now taked 3.7 minutes. Impact of this change is expected to be limited as the instrument set-up is  absorbed in the telescope preset, and grating change is normally not allowed within an OB without a waiver.
  • MUSE, the Multi-Unit Spectroscopic Explorer, is in operation since Period 94. MUSE is a second-generation VLT instrument located on the Nasmyth platform B. It is a large-format integral-field spectrograph, based on image-slicing technology, and has a modular structure composed of 24 identical Integral Field Unit modules that together sample a contiguous 1 arcmin2 field of view in Wide Field Mode (WFM) sampled at (0.2 arcsec)2/spaxel. MUSE will initially be used in seeing limited WFM only.
    MUSE will later exploit the VLT Adaptive Optics Facility in combination with the GALACSI AO module. When offered, it will provide Ground Layer AO correction for the WFM. In the future, a Narrow Field Mode (NFM) will also be made available, and will cover a ~(7.5 arcsec)2 field of view sampled at (0.025 arcsec)2/spaxel with Laser Tomography AO correction.
  • Adaptive Optics Facility
    During Periods 94 and 95 the following installation and commissioning activities will affect operation on UT4. Although the dates provided are the best estimates at the time of writing, they can be affected by significant shifts. Large and monitoring programmes must be compatible with tese activities.
    • installation and commissioning of the first Laser Guide Star Unit (LGSU) will take place in Period 94 (March 2015);
    • installation of GRAAL on the telescope will take place early during Period 95 during which HAWK-I is  not available;
    • a 10-night run for the commissioning of GRAAL with the first LGSU will then follow during which UT4 will not be available for operation with any instrument;
    • the installation of the 3 other LGSUs will likely take place in June during which the telescope will not be available;
    • commissioning of these 3 LGSUs is then expected to take place in July during which the telescope will not be available for 10 nights;
    • a 10-night run for the  commissioning of GRAAL with all LGSUs is expected to take  place  in September during which the telescope will not be available for operation.

Visitor focus

  • No focus for Visitor Instrument is available on the VLT in Period 95.

VLTI instruments and facilities

Starting in March 2015 and during Period 95, the laboratory will undergo major modifications in view of the arrival of the 2nd generation instruments GRAVITY and MATISSE as well as ESPRESSO, which will go in the nearby combined-Coudé laboratory. As consequence, MIDI will be decommissioned in March 2015, during Period 94, and AMBER and the Visitor Instrument, PIONIER, are not offered in Period 95. AMBER and PIONIER will be offered again in Period 96.

Survey Telescopes and Instruments



  • Normal  programme  proposals  are   accepted  on  the  VST  in Period 95 for  the first time. In order to ensure the timely progress of  the ongoing Public Surveys these are restricted to  filler programmes that request poor weather conditions (i.e., no moon constraints, seeing 1.4 arcsec, thin/thick clouds). Target of Opportunity proposals requesting  a short amount of time with OmegaCAM will also be considered.
  • The installation of an improved baffling mechanism on the VST was completed on April 2014. The new baffles are designed to reduce the amount of stray-light component in OmegaCAM images:  measurements show that  stray-light in each band has indeed been reduced by 6%.. Even if the amount of stray-light component is reduced, some residual stray-light is still visible. As a further improvement,  the new baffling mechanism will be provided with a new specially designed system of ribs that will remove most of parasitic light coming from the Moon, bright stars stars and the sky. A prototype was positively tested on two nights on June 14 and 16. The final ribs' system is expected to be installed by the end of 2014.