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

This section describes important changes which took place during Period 94 and 95, as well as changes expected to take place during Period 96.


  • Seeing and Image Quality:  Starting from Period 96, the  seeing information  to provide in Box  3 of a  proposal is the seeing in the V band  at zenith.  This change now ensures that the scheduling tool uniformly takes the seeing into account. Service mode users for approved programmes will enter the Image  Quality for the airmass and  wavelength of interest required for their observations as constraint during Phase 2. The Messenger article `On the Difference between Seeing and Image Quality: When the Turbulence Outer Scale Enters the Game' by P. Martinez et al. describes the meaning of these two quantities.
    Accordingly, the Exposure Time Calculators have been modified and clearly distinguish between the two quantities, using a slightly modified version of the formula given in the above article.

Exposure Time Calculators:

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. 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 96. It is expected to be back in operations in 2017.
  • Instead, NACO has been offered on the Nasmyth A focus since Period 94, with a limited list of offered modes.
    • During Period 96, only the following modes are offered:
      • NAOS:
        • VIS & IR wavefront sensing
        • Pupil tracking
      • CONICA:
        • Imaging without chopping, in NoAO; usage of the Mp filter is only possible in VM
        • Cube mode
        • Focal plane AGPM coronography
        • Wollaston/HWP polarimetry
        • Grism Spectroscopy
        • SAM/SAMPOL, only in VM.
    • The following modes are not offered: LGS, SDI+, 4QPM/Lyot coronography, APP imaging and spectroscopy, prism spectroscopy.
    • As for February 2015, the Aladdin2 detector (installed in CONICA at the end of 2014) features a spurious background noise that limits the sensitivity of NACO when long individual exposure times (DIT) are used. This extra noise is caused  by an imperfect thermal shielding of the detector electronics.
      Nearly wavelength-independent, the contribution of the background noise can be modeled as a brighter sky: about -0.6 mag/arcsec through the Ks-band filter and -0.7 mag/arcsec through the H-band filter. There is no significant degradation at long wavelengths (L’, M’) as observations anyway require short DITs due to the nigh ambient background (sky + optics).
      It is possible that an intervention will take place to reduce this additional noise significantly before the start of P96: please check the News page for updates. If this noise is not reduced significantly by then, it is recommended to use DIT shorter than 10 seconds. The FowlerNsamp readout mode will not provide a improved sensitivity as long as this extra background noise dominates. If your programs requires longer DITs, please contact and/or take this background into account when running your SNR calculations (i.e with the ETC).
    • Large and Monitoring Programmes with NACO will not be accepted as the availability of several modes cannot be guaranteed in the coming periods.
  • FORS2: The prisms  of the Longitudinal Atmospheric Dispersion Corrector (LADC) located in front of the instrument have been exchanged by the ones of FORS1 whose coating has been removed. This led to a gain in throughput of 0.1 ( in the blue), 0.07 (in V), 0.05 (in I), and 0.04 (in I) mag, due to a reduction of the scattering introduced by the degraded coating. The improved uniformity of the transmission across the field-of-view allows one to use FORS2: for precise differential photometry and spectro-photometry, especially transmission spectroscopy for studies of exoplanets.
  • 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 is taken place 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. 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. 
      A project to fix the ADC systems has started. XSHOOTER will likely be taken out of operations - possibly for several months - to modify the ADC system or install re-designed ones in the future. As a consequence, Large and Monitoring Programmes using XSHOOTER will not be accepted in Period 96. Updates on the status of the ADCs can be found on the XSHOOTER news webpage.
    • Starting with Period 96, two additional templates in slit and IFU modes are  available for mapping of an extended object with a sequence of offsets and with or without any sky position. In parallel, the behavior for the FixedSky and GenericOffset  is slightly changed. The FixedSky offset template allows one to observe the object and a defined, allways identical, sky position. The GenericOffset template allows one to observe an object or a sequence of objects and a sequence of sky positions, which can be different, but the number of sky observations must be equal to the number of object observations. These changes allow a better support by the data reduction pipeline.
    • 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.
    • The coating of the Giraffe HR grating was cleaned at the end of January 2015 to improve efficiency by approximately 20%.
    • A redetermination of the focus of the instrument has been carried out. As a result, the spectral resolution has significantly improved, as summarized in the FLAMES News page.
    • FLAMES will likely be decommissioned in 2017 to provide space for CRIRES following its upgrade. Consequently, Large and Monitoring Programmes involving FLAMES will not be accepted.

UT3 - Melipal

    • (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 has been offered since Period 95.
    • Starting from Period 96, the IRDIS DPI mode is offered in Visitor Mode only.
  • VISIR was again offered in Period 95. The offered modes  include imaging, low-resolution specctroscopy, and long slit and cross-dispersed high-resolution spectroscopy. The coronagraph Annular Grooves Phase Mask (AGPM) mode is offered pending successful commissioning early in March 2015: interested users should check the VISIR News page for update and relevant information. Only Large and Monitoring programmes involving imaging, low-resolution specctroscopy, and long slit and cross-dispersed high-resolution spectroscopy will be accepted.
  • VIMOS:
    • Since Period 95, rules regarding attached calibrations for the MOS mode have updated.  For the more accurate grisms LR_blue, LR_red and HR_red (<1 pixel) the previously implemented waivable error has been converted to a warning. That is, users can create their MOS OBs without attached calibrations, but need to check that their science case can accept wavelength accuracies of 0.5-1.0 pixels. For the less accurate grisms HR_Blue, MR, and HR_orange the waivable error remains in place.
    • Large and Monitoring Programmes are offered again in Period 96 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.
    • Starting with 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.

UT4 - Yepun

  • Adaptive Optics Facility
    During Periods 95 and 96 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 these activities.
    • installation of the first Laser Guide Star Unit (LGSU) is taking place in Period 94 (March 2015); it will be commissioned during Period 95;
    • installation and commissioning of GRAAL on the telescope will take place in August 2015 during which HAWK-I is not available during  approximately one month;
    • a 10-night run for the commissioning of GRAAL with the first LGSU will take place early in Period 96 during which UT4 will not be available for operation with any instrument;
    • the installation of the 3 other LGSUs and commissioning of GRAAL with all LGSUs will likely take place during the second half of Period 96, during which the telescope will not be available for operation with any instrument during approximately 3 weeks spread over 3 months.
  • 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. Starting from Period 96, users may control the adapter focus from the acquisition template therefore allowing out-of-focus observations.
    • The filter NB1190 has replaced back the visitor filter NB0984.
    • The detector persistence limits have been revised.
    • 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;
    • an upgrade of the SPIFFI  optics is foreseen to take place during Period 96.  Its scope and schedule are being finalized  as this  call  is  released. Improvements  may include  replacing J and K filters by new ones with  higher  transmission, replacement of the pre-optics by one with better transmission in the J band, and replacement of mirrors by ones with better  surface quality to improve the line spread functions.  The instrument will therefore not be available for approximately 1 month likely to start in January 2016.
  • 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.
    • MUSE is available for observations in Rapid Response Mode.

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  undergoes 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.
  • MIDI is  decommissioned in March 2015 and is not offered anymore.
  • AMBER is  offered again in Period 96.
  • PIONIER is offered again in Period 96, as an ESO instrument: therefore, it is no longer mandatory to contact the instrument team or to include them as co-I before submitting the proposal. It is available in both service and visitor modes.  Follow late breaking news from technical time results in March, 2015:
    • The instrument can track fringes on visibilities higher than 5%  (V=0.05)
    • The LOW detector gain has been commissioned. The brightest  targets that can be observed in service mode are H=-1mag. Since no suitable calibrators might be available for the LOW gain within the recommended area around the target,  cross-calibration with other gain values has been tested and is  within the typical precision of the instrument. In that case, calibrators well fainter than the target can be used.
    • Tests on the UTs have shown no improvement of sensitivity or  precision over the ATs. UTs can only be requested if use of ATs is excluded (e.g. no guide star available).
  • The AT configurations have slightly changed, but the overall characteristics remain. Three different AT quadruplets are offered for P96 (check the VLTI configuration page for more information):
    • small (baselines from 10 to 40m): A0-B2-C1-D0 to replace A1-B2-C1-D0
    • medium (baselines from 40 to 100m): K0-D0-G2-J3 to replace H0-D0-G1-I1
    • large (baselines from 60 to 140m): A0-J2-G1-J3 to replace A1-K0-G1-J3 
  • The ATs will be equipped with different really optics to provide optimum field of view and pupil relay. Even if the transmission of these optics is lower, the improvement in pupil re-imaging should compensate and allow to offer the same limiting magnitudes.

Survey Telescopes and Instruments



  • Normal programme proposals are accepted on the VST in Period 96. However, 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, and/or seeing>1.4", and/or 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.