Important recent changes (since Period 100) regarding Paranal instrumentation and facilities

This section describes important changes which took place during Periods 100 and 101, as well as changes expected to take place during Period 102.


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 experienced 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.

After being used successfully in Period 101 Service Mode preparation for instruments on UT2, VST and VISTA, ESO is now extending the use of p2 for all Paranal instruments.

Users are invited to familiarise themselves with the tool via a demo web interface that does not require having a scheduled observing run; in particular, it allows users to obtain a detailed overheads computation for the supported instruments.

Further information is available on the p2 webpages.

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 of 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  POEM Instructions webpage.  

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. 2010 (The ESO Messenger 141, 5) "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 stellar images 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 stellar image along the entrance slit of a spectrograph increases the total signal collected in a single spectrum by a factor of up to 100 relative to a perfectly shaped image for bright sources within 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 102 NACO 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 period and that NACO will be decommissioned in Period 104.
  • FORS2:
    • Since Period 101, two additional narrow-band filters have been offered in Visitor Mode. 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.
    • As discussed in the Call for Proposals for Period 101, ESO has decided to decomission the high time resolution modes (imaging, HIT-I; spectroscopy, HIT-S; and multi-object spectroscopy, HIT-MS), due to their low demand and high overhead for the observatory. HIT modes will not be offerred in Period 102, nor in future semesters.
  • KMOS: 
    • Since Period 98  KMOS operates with 23 arms instead of 24, as performance of arm #3 is degraded and cannot be used in operations. Since Period 100 Arm #1 is experienciencing throughput losses, even though it can still be deployed on sky. An intervention is planned in Period 101 to repair both arms. Updates on the status of Arm #1 and #3 can be found on 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. Instead, users are encouraged to use the Molecfit tool, which can provide accurate telluric line corrections in most cases. From Period 102, the observatory will obtain one telluric standard star with the slit widths used for each science observation during the night, which can be used to improve the telluric correction. No airmass and no time window constraints will be imposed on these telluric standard star observations. 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).
    • Starting with Period 102:
      • dithering is offered for IRDIS/DPI;
      • the IRDIS/LSS mode is offered also in service mode;
      • a new SLLC apodizer is offered for the IRDIS/LSS mode.
    • Zelda mask day calibrations may offer AO performance improvements by correcting non-common path wave front errors. The corrections are expected to be applied automatically to all infrared modes during Period 102.
    • VISIR is only offered until late November 2018, as the instrument will be dismounted from UT3, modified and installed on UT4 to allow it to use the Deformable Secondary Mirror for the New Earths in the α Cen Region - NEAR experiment. It will not be o ffered during the duration of the experiment. As a consequence, Monitoring and Large programmes will not accepted during Period 102.
    • 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.
  • VIMOS is being decomissioned at the end of Period 100. As a consequence VIMOS has been 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 102 and Period 103. Depending on successfull commissioning, CRIRES will be o ffered in Period 104.

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 has been off ered since Period 101 in its Ground Layer Adaptive Optics (GLAO) 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 GALACSI in its Laser Tomographic Adaptive Optics (LTAO) mode started during Period 100 and continues during Period 101. The combination of this mode with MUSE in Narrow Field Mode is being commissioned during Period 101 with the aim of offering it in Period 103.
    • Due to the large existing commitment on UT4,  Large and Monitoring programmes are not offered 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.
    • The combination of HAWK-I and GRound layer Adaptive optics Assisted by Lasers (GRAAL) has been successfully commissioned during Period 100 and is offered for the first time in Period 102.
    • Due to the large existing commitment on UT4,  Large and Monitoring programmes are not offered in Period 102.
    • During January 2018,  SINFONI underwent an intervention to change the motor for the pre-optics wheel and various maintenance tasks. The results are summarised in the SINFONI news section.
    • SINFONI will be dismounted from UT4 during the second half of Period 102 and moved to UT3, as VISIR will be mounted on UT4 for the NEAR experiment. As a consequence, no observations requiring the Laser Guide Star will be executed during the last weeks of Period 102.
    • Large and Monitoring programmes for SINFONI will not be accepted in Period 102 as the instrument will be decommissioned in Period 103 so that SPIFFI can be integrated in ERIS.

Incoherent combined focus

    •  The Échelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations is located at the Incoherent Combined Coudé Focus (ICCF). Its commissioning in 1-UT mode started during Period 100 and continues in Period 101. The 1-UT mode is o ffered starting in Period 102.
    • Two basic observing modes are thus available: (1) the High Resolution (HR) mode providing a spectral resolution of 140 000, with the diameter of the fibre aperture on sky of 1"; and (2) the Ultra High Resolution mode (UHR), providing a spectral resolution of 200 000, with the diameter of the fibre aperture on sky of 0.5".
    • The Laser Frequency Comb (LFC) is operational but not yet fully tested. Users are suggested to take LFC frames as additional calibrations to benefit from the full precision of ESPRESSO once the pipeline recipes are optimized.
    • The 4-UT mode will provide a medium resolution of 59 000 with the diameter of the fibre aperture on sky of 1". Depending on successfull commissioning in Period 101 this mode will be off ered in Period 103.

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 will be completed during Period 101 and will result in an improvement of throughput.
    • The installation, veri cation and commissioning of NAOMI, the New Adaptive Optics Module for Interferometry - a low-order adaptive optics system for the ATs - starts in Period 101 and is expected to be completed by the end of November 2018. Operations will not be possible at the start of Period 102 until the end of the NAOMI commissioning.
    • Since 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.
    • ESO is developping a scheme to optimise operations for aperture synthesis with the VLTI. This scheme requires that proposals aiming at imaging reconstruction with PIONIER or GRAVITY with the ATs include the sentence "This program aims at collecting VLTI data for reconstructing images." using the \SpecialRemarks macro. In addition, such proposals should request time corresponding to at least six concatenations (CAL-SCI for GRAVITY or CAL-SCI-CAL-SCI-CAL for PIONIER) per object and per AT con guration. They should also specify the maximum period over which data can be collected, based on the expected evolution time scale of the target, with a minimum of ten days due to operational constraints.
    • Due to the large number of activities aff ecting the operations on the ATs, the commissioning of MATISSE and existing commitments, no Monitoring or Large programme will be accepted in Period 102 with the ATs.
  • Instruments:
    • AMBER will be decommissioned at the end of Period 101. It is therefore not offered in Period 102.
    • 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 both Service and Visitor mode.
      • For dual-fi eld observations, swapping between two targets is now possible.
      • ESO invites proposals with the goal of performing astrometric measurements, a capability of GRAVITY which is still under development (see, e.g., GRAVITY Collaboration 2017 A&A 602, A94 or The ESO Messenger 170, 10). Proposers who wish to use the astrometric capability and contribute to its development are invited to consult the GRAVITY webpage and contact the astrometric team.
    • The installation of Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE) took place during Period 100. Its commissionning, started in Period 100 will continue in Periods 101 and Period 102.
    • No VLTI Visitor focus is available in Period 102.

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 101. The remaining surveys will continue through Period 102, and possibly beyond. Seven second generation 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. 
  • Approximately 5-10 percent of VISTA observing time is available for open time proposals. Particularly encouraged are open time proposals requesting any weather conditions (THIN and seeing >= 1.2"), for which there is low demand from the public surveys.
  • As of P101 the phase2 OB preparation are done via the web-based tool p2.


  • Starting with Period 101, the zenith avoidance distance is set to 7 degrees to minimise problems with ellipticity near the zenith.
  • Normal, Monitoring and Large programme proposals are accepted on the VST in Period 102. 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 been updated in December 2017.