Important recent changes (since Period 95) regarding Paranal instrumentation and facilities

This section describes important changes which took place during Period 95 and 96, as well as changes expected to take place during Period 97.


  • 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).
  • The installation and commissioning of the Coudé train for ESPRESSO will take place during Period 97.

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 97. Operations will likely not start before the end of 2017.
  • Instead, NACO has been offered on the Nasmyth A focus since Period 94, with a limited list of offered modes.
    • During Period 97, 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, with the  Lp, NB_3.74 or NB_4.05 filters;
        • Wollaston/HWP polarimetry;
        • SAM/SAMPOL, only in VM.
    • The following modes are not offered: LGS, SDI+, 4QPM/Lyot coronography, APP imaging and spectroscopy, prism spectroscopy, and, starting with Period 97, grism spectroscopy, and coronagraphy other than the AGPM coronagraphy.
    • 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).
      Following problems with the camera wheel, NACO was fixed with the S13 objective on June 8th, 2015.  In addition, following a power cut on June 14, 2015, the upper right quadrant is not suitable for science. The 3 problems are expected to be solved during a 2-month long intervention starting early in October 2015. Please check the News page for updates.
      In particular, the current NACO ETC over-predicts the flux in JHK by up to 50 percent. An improved version will be delivered for Phase 2, after the intervention in October/November; this new version will take into account the  reduced background and also measurements in bands red-wards of K.
    • Large and Monitoring Programmes with NACO will not be accepted as the availability of several modes cannot be guaranteed in the coming periods.

UT2 - Kueyen

    • A project to fix the Atmospheric Dispersion Correction (ADC) systems started in 2015. 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 97. Updates on the status of the ADCs can be found on the XSHOOTER news webpage.
    • Starting from 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 ETC. 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.
    • A redetermination of the focus of GIRAFFE has been carried out. As a result, the spectral resolution has significantly improved, as summarized in the FLAMES News page.
    • An alternative, low noise read-out mode for GIRAFFE is offered for Period 97, in Visitor Mode only.

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.
    • Starting from Period 97, the broadband H filter for IRDIS is offered in IRDIFS mode, while the broadband Ks filter is offered in the IRDIFS_EXT mode.
    • As described in the CPI section of the SPHERE Overview, the quality of the correction strongly depends on the seeing: in particular,  seeing conditions for SPHERE proposals must be better than 1.4"
  • VISIR is offered again since Period 95.
    • The offered modes include imaging, low-resolution specctroscopy, and long slit and cross-dispersed high-resolution spectroscopy in both Service and Visitor Modes. Coronagraphy using the Annular Grooves Phase Mask (AGPM)  is offered in Visitor Mode only. Details on the offered modes and configurations are provided in the User Manual.
    • Only Large and Monitoring programmes involving imaging, low-resolution specctroscopy, and long slit and cross-dispersed high-resolution spectroscopy will be accepted.
    • The PWV must be provided as an observing constraint during their Phase 1 and Phase 2 preparation.
  • 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.
    • Starting 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.
    • Large and Monitoring Programmes are not offered in Period 97 for operational reasons compounded by the ongoing Public Spectroscopic Surveys.
    • Public Spectroscopic Surveys started in Period 94 and substantially use all the dark and grey time in good conditions (PHO/CLR, seeing < 1.000) in RA ranges 00-05:30h and dark time in RA ranges 08-12h (also see the Public Survey webpages). Please note that even though the best observing conditions in the RA ranges above are substantially committed to the ongoing Public Spectroscopic Surveys, some time may be allocated to a very strong, scientifically compelling Normal or DDT programme.

UT4 - Yepun

  • Adaptive Optics Facility
    • Installation of the first Laser Guide Star Unit (LGSU) took place in March 2015. It was commissioned during Period 95;
    • GRAAL was installed on the telescope in August 2015.
    • During Periods 96 ad 97 the following installation and commissioning activities 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) took place in March 2015 and was commissioned during Period 95;
      • installation of GRAAL on the telescope and re-commissioning of HAWK-I took place in August 2015;
      • commissioning of GRAAL with the first LGSU takes place early in Period 96;
      • installation of the 3 other LGSUs and commissioning of common features with all LGSUs and GRAAL takes place during the second half of Period 96
      • commissioning of the 4 LGSus will continue early in Period 97 during which the telescope is not available for about 10 nights.
  • HAWK-I :
    • Starting from Period 96, users of Fast Photometry may control the adapter focus from the acquisition template therefore allowing out-of-focus observations.
    • An upgrade of the SPIFFI  optics is planned for January 2016: its main goal is to improve transmission in the J band. Changes are expected to include:
      • Replacement of pre-optics including the pre-optics wheel.
      • New J and K filters with improved transmission. The filter wheel will also be changed.
      • Replacement of mirrors to improve the line spread function (LSF).
      • Enlarged sky baffle to cure vignetting of slits #1 and #32.
  • MUSE:
    • Starting from Period 96, MUSE has been available for observations in Rapid Response Mode.

Visitor focus

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

VLTI instruments and facilities

  • During Period 95 the laboratory underwent 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.
  • AMBER is  offered again since Period 96.
  • PIONIER is offered again, as an ESO instrument, since Period 96: 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).
  • VLTI-UTs and ATs: By early Period 97, all UTs Coudé and all ATs will be exclusively equipped with Star Separator Systems (STS) in view of operations with
  • Starting from Period 96 the AT configurations have slightly changed, but the overall characteristics remain. Three different AT quadruplets are offered for Period 97 (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 installation of GRAVITY, the second generation VLTI instrument for precision narrow-angle astrometry and interferometric imaging, starts in 2015 during the VLTI laboratory refurbishment. Commissioning of the instrument starts during the first half of Period 96 and will continue during Period 97: during this time the VLTI will not be available for regular operations for approximately 2 weeks every 2 months. The number of baseline configurations for the ATs may also be restricted during the second half of the period due to these commissioning activities.
  • The installation of the 4 units of the GRAVITY Coudé Infrared Adaptive Optics (CIAO) system for the VLT Interferometer is expected to take place during Period 96 and 97, during which the corresponding UT will not be available for VLTI operation. The commissioning of each of these units is expected to require approximately 10 half-nights.
  • No VLTI Visitor focus is available in Period 97.

Survey Telescopes and Instruments



  • Normal programme proposals are accepted on the VST in Period 97. 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 including specially designed system of ribs was completed in April 2015. Measurements show that most of the stray-light component has been reduced. Also, the brightness of the background is at least 10% fainter than before the installation of the ribs and baffles.