Important recent changes (since Period 99) regarding Paranal instrumentation and facilities

This section describes important changes which took place during Period 99 and 100, as well as changes expected to take place during Period 101.


Excellent condition proposals:

Seeing at Paranal is better than 0.5" for 5-10% of the time, while episodes of precipitable water vapor smaller than 0.5mm are encountered 6 to 7 nights per year (see Kerber et al. 2014, MNRAS 439, 247) mostly during the southern hemisphere winter. ESO encourages the unique science that can be carried out under one or both of these conditions: proposals designed to take advantage of one of these conditions should include the mention \Excellent condition proposals" in the \SpecialRemarks macro in the ESOFORM proposal form. Users requiring excellent seeing conditions should specify 0.4" in the \ObservingRun macro in their proposal. The proposals should describe why the science can only be achieved in such conditions.

Preparation tool in Service and Visitor Mode:

ESO has recently implemented the new web application p2 in order to allow for more agile preparation and execution of Visitor Mode and Designated Mode observations on Paranal.

This web application is being expanded

  1. to cover also Service Mode observations, and
  2. to o ffer the possibility of using scripts for
    • the creation or modi fication of Observing Blocks for both Service Mode and Visitor Mode users, and
    • the creation or modi fication of the execution sequence for Visitor Mode users.

The deployment of p2 for Service Mode observation preparation will follow a gradual schedule and may start in Period 101, likely on a limited basis. When necessary, Service Mode users will be contacted at the start of Phase 2 preparation period.

Paranal Observatory Eavesdropping Mode

Since Period 100, a new web tool called POEM (Paranal Observatory Eavesdropping Mode) has been offered for delegated visitor mode observations. POEM transmits a live image of the instrument workstation screen to the observer’s web browser, in view-only mode. No software installation is required, apart from a modern web browser. POEM complements the web application p2 to allow the user to monitor and modify observations in real time. Details will be available in the Paranal Science Operations webpage, once the tool is commissioned.

Seeing and Image Quality:

  • The seeing information to be provided in Box 3 of the proposal form is the seeing in the V band at zenith. This 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 a constraint during Phase 2. The article by Martinez et al. "On the Difference between Seeing and Image Quality" describes the meaning of these two quantities and further information can be found on the Observing Conditions webpage.
  • The Exposure Time Calculators have been changed accordingly and clearly distinguish between the two quantities, using a slightly modi fied version of the formula given in the above article. The ETCs also report on the probability to achieve the input seeing conditions and the resulting image quality.

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

  • NACO:
    • During Period 101 is offered for the following modes
      • NAOS:
        • VIS & IR wavefront sensing;
        • Pupil tracking;
      • CONICA:
        • Imaging without chopping, in NoAO;
        • Cube mode;
        • Focal plane AGPM coronography, with the  Lp, NB_3.74 or NB_4.05 filters;
        • Wollaston/HWP polarimetry;
        • SAM/SAMPOL.
      • In contrast to periods anterior to 99, observations should preferably be executed in Service Mode, except for SAM/SAMPOL. PIs requesting Visitor Mode for the other modes should carefully justify their request.
    • Large and Monitoring Programmes with NACO will not be accepted as the availability of several modes cannot be guaranteed in the coming periods.
  • FORS2: two additional narrow-band filters are offered in Visitor Mode in Period 101. These are 'FILT_753_8+89' (central wavelength of 7528 Å, FWHM 60 Å), and 'FILT_621_5+87' (central wavelength of 6195 Å, FWHM 60 Å). A full characterisation of these filters is ongoing, and potential users are encouraged to contact in advance of proposal submission.
  • KMOS: 
    • Since Period 98 and most probably for the entire Period 101, KMOS operates with 23 arms instead of 24, as performances of arm #3 are degraded and cannot be used in operations.  Its repair or replacement will not take place before the next maintenance of the closed-cycle cryo-coolers. Updates on the status of Arm #3 can be found on the KMOS news webpage.
    • During Period 99 a dirt pattern appeared on the focal plane of detector #1. At the time of issuing this call, the flake moved out and is no more affecting the data quality. Users should be aware that new occurences could appear, and regularly check the KMOS news webpage.
    • Since Period 100, a new KARMA version is available (version 2.7). This version should be used for the preparation of the KARMA set-up files. The new software allows to continuously observe a target throughout the whole nodding cycle, thus optimizing the observing time at the telescope.

UT2 - Kueyen

    • Atmospheric Dispersion Correction (ADC) is available again after the installation of re-designed systems in May 2017.
    • Starting with Period 101, the calibration plan does not include observations of telluric standard stars anymore. Instead, users are encouraged to use the Molecfit tool, which can provide accurate telluric line corrections in most cases. The X-shooter News web page and User Manual list a set of criteria for which observation of a telluric standard star is recommended and for which execution time must be included in the phase 1 proposal.

UT3 - Melipal

    • As described in the CPI section of the SPHERE Overview web page, the quality of the correction strongly depends on the seeing: in particular,  seeing constraints for SPHERE proposals must be better than 1.2", or smaller for targets which cannot be observed at low airmass.
    • Since Period 100, 
      • Rapid Response Mode is offered for the ZIMPOL imaging and polarimetry modes, IRDIS classical imaging mode and IRDIFS imaging mode.
      • Sparse Aperture Mask (SAM), a 7-hole mask design inserted in the pupil plane (Lyot Wheel), is offered. Sparse aperture masking works only in Pupil Tracking mode in order to stabilise the Fizeau interferometrer created by the 7 apertures. SAM can be used with the modes IRDIS_CI, IRDIS_DBI, IRDIS_DPI, IRDIFS, IRDIFS_EXT and ZIMPOL_I.
      • IRDIS_DPI is now available in Pupil Tracking mode.
      • Targets with R>11 are allowed in Service Mode. Since they require the best possible conditions, users should request them with a seeing contrainst <= 1.0". For R> 11, H>9 targets, coronagraphs should be avoided as SPHERE might be operated without precise drift control on the focal-plane mask (DTTS-free mode).
    • Since Period 99, acquisition has been allowed in the K-band in imaging mode.
    • The PWV must be provided as an observing constraint during Phase 1 and Phase 2 preparation.
    • Service Mode programmes that require 1.2" seeing or worse are actively encouraged.
    • Monitoring and Large programmes will not accepted during Period 101 as VISIR will be used for the New Earths in the Cen Region - NEAR experiment, and will not be offered for regular operations starting early December 2018 until the 2nd semester of 2019.
  • VIMOS is being decomissioned late in Period 100 or early in Period 101. As a consequence VIMOS is not offered any more starting with Period 101.
  • Following its upgrade into a cross-dispersed spectrograph, CRIRES will be installed on the UT3-Melipal Nasmyth B focus (instead of VIMOS) and commissioned  in Period 101 and Period 102. Depending on a successfull commissioning, CRIRES will be o ffered in Period 103.

UT4 - Yepun

  • MUSE
    • Ground Atmospheric Layer Adaptive Corrector for Spectroscopic Imaging (GALACSI), the Adaptive Optics module for MUSE, was commissioned during Period 99. This combination is off ered for the first time in Period 101 in its Ground Layer Adaptive Optics mode to correct the MUSE Wide Field Mode. The full capabilities of MUSE+GALACSI in this mode are currently been characterised and interested users should check the instrument News web page for details.
    • Commissioning of MUSE and GALACSI in Narrow Field mode with AO takes place during Period 100 and Period 101. Depending on its successful commissioning, this combination will be o ffered in Period 102.
  • HAWK-I :
    • Since Period 100, users can request the same subwindows for skyflats and/or twilight flats as for the science data.
    • Commissioning of HAWK-I and GRound layer Adaptive optics Assisted by Lasers (GRAAL) takes place during Period 100. Depending on its successful commissioning, this combination will be off ered in Period 102.
    • Since Period 99, observations of moving target can take advantage of the Adaptive Optics (AO) capabilities of SINFONI. Adaptive optics offers an improvement in image quality and/or in S/N of the final spectra compared to noAO. Bright asteroids and comets (R < 14 mag) can be used as the AO reference "stars" in NGS mode. For fainter moving objects (14 < R < 17 mag), the science target itself can serve as a Tip-Tilt "star" in LGS mode. For science targets that have differential tracking rates higher than 0.04"/s in either RA or DEC, visitor mode is mandatory if AO-aided observation is requested. The R magnitude for comets is referred to as nuclear magnitude ("N-mag"). The user should check the news section of the SINFONI web page for any updates.
    • Large and Monitoring programmes for SINFONI will not be accepted in Period 101 as the instrument will be decommissioned in Period 104 so that SPIFFI can be integrated in ERIS.

Incoherent combined focus

  • ESPRESSO: The  commissioning of the Coudé trains continues in Period 100. The spectrograph installation and first commissioning in 1-UT mode take place during Period 100 and 101. Depending on successful commissioning, the instrument will be o fffered in Period 102 in 1-UT mode.
  • Commissioning in 4-UTs mode will continue in Period 101.

Visitor focus

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

VLTI instruments and facilities

  • General:
    • ESO aims to increase the fraction of service mode for VLTI observations. PIs requesting visitor mode for VLTI should carefully justify the need for this mode.
    • Proposers should be aware that there is a minimum time limit of 1 night per baseline configuration for Visitor Mode runs requiring VLTI-AT observations. Proposers requiring shorter runs per baseline configuration should specify Service Mode observations. These restrictions do not apply to the VLTI-UT baselines.
  • VLTI-ATs:
    • The refurbishment of each of the 4 ATs continues during Period 101 in order to increase the throughput of their optical Coudé trains as well as to improve their operational reliability signi cantly: in Period 101, several primary mirrors will be recoated. New limiting magnitudes will be assessed at the end of the intervention. New limiting magnitudes will be assessed at the end of the intervention.
    • No operations will take place with the VLTI for approximately 2.5 months during Period 101, in order to carry out the installation, verifi cation and commissioning of the New Adaptive Optics Module for Interferometry (NAOMI), the low order adaptive optics system for the ATs. A detailed schedule is unfortunately not available at the time of writing this document.
    • Due to the large number of activities aff ecting the operations on the ATs, no Monitoring or Large programme will be accepted in Period 101.
    • Starting from Period 101, the AT astrometric con guration A0-G1-J2-K0 is off ered for GRAVITY in Dual Field mode only (see the baseline con figuration webpage). In order to limit idle time, Service Mode programmes requesting the Large configuration (A0-G1-J2-J3) might see their observations executed on the astrometric confi guration instead, as the baselines show similar length and sky coverage.
  • Instruments:
    • AMBER: ESO encourages users of AMBER to utilize Period 101 to complete any on-going programme considering that it will be decommissioned in Period 102 to make space for a visitor focus in the VLTI laboratory. AMBER is not offered for Large or Monitoring programmes.
    • ESO offers GRAVITY on all AT configurations as well as on all four UTs with the visible (MACAO) and infrared (CIAO, in off-axis mode only) adaptive optics system in service mode only.
      • The astrometric mode is not offered.
      • Limiting magnitudes both at the bright and faint ends have been updated following performance assessment during commissioning: see the GRAVITY instrument description web page.
      • Commissioning of the astrometric mode on both ATs and UTs continues in Period 101.
    • The installation of Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE) takes place during Period 100. Its commissionning will require three 2-week runs during Period 101. It is expected that a similar amount will be required in Period 102.
    • No VLTI Visitor focus is available in Period 100.

Survey Telescopes and Instruments


  • It is foreseen that further VISTA Public Surveys from the first cycle will have completed their observations at the end of Period 100. The remaining surveys will continue through Period 101, and possibly beyond. Seven new Public Surveys, essentially spanning the whole RA range have started observations in Period 99 and are expected to last until 2019.  See the Public Surveys page for details. The fraction of the VISTA observing time devoted to Public Surveys  is similar to the one of previous periods. Some fraction of observing time will be available for open time projects. Particularly encouraged are open time proposals requesting bad weather conditions (THIN and seeing >= 1.2"), for which there is a significant amount of time available to the community.


  • Normal, Monitoring and Large programme proposals are accepted on the VST in Period 101. However, in order to ensure the timely progress of the ongoing Public Surveys, Normal, Monitoring, and Large programmes are restricted to filler programmes that request poor weather conditions (i.e., no moon constraints, and/or seeing>1.2", and/or thin/thick clouds). Target of Opportunity proposals requesting a short amount of time with OmegaCAM will also be considered.
  • Please check that you use the most recent version of the ETC when preparing your proposal as throughputs have recently been updated.