Paranal: Important recent changes regarding instrumentation and facilities

This section describes important changes which took place during Period 111, as well as changes expected to take place during Periods112 and 113.


Distributed Peer Review:

Starting from Period 110, ESO employs Distributed Peer Review (DPR) for approximately half of the submitted proposals. In this paradigm, first introduced by Merrifield & Saari (2009), all PIs of proposals qualifying for DPR accept to review a number of proposals (N) submitted by their peers during the same cycle. Correspondingly, they accept that their proposals are reviewed by N peers who submitted proposals in the same cycle. More details and background information on DPR at ESO can be found in Patat et al. (2019). Users should familiarise themselves with the DPR rules and guidelines.
In Period 111, N = 10, and the criteria describing the proposals which qualify for DPR are as follows:

  1. All proposals requesting a total time (including overheads) less than 16 hours are assigned to DPR. This time threshold is set to have an approximate 50/50 distribution between DPR and panels, and it is based on the time request statistics compiled in recent cycles.
  2. Exceptions to this general rule are proposals including at least one ToO run, and DDT proposals.
  3. All other proposals submitted during a regular cycle will be reviewed in the classical way by the OPC and the panels.

In Period 113, the review channel (DPR vs. panels) is assigned at the time of proposal submission, based on the above rules. The PI (or delegated PI; dPI) is informed about the assigned review process and prompted to formally accept the conditions at the time of submission. At this stage the PI/dPI can delegate the reviewer’s role to one of the co-Is listed in the proposal. The delegation can also occur when the list of co-Is is specified.

By submitting a proposal qualifying for DPR, the PI/dPI commits to follow the DPR rules (see DPR rules and guidelines).

New scientific keywords:

Since Period 110, a new set of scientific keywords replaces the OPC categories. While preparing their proposals in p1, users must select at least two keywords, and at most five keywords (ten keywords for Large Programmes), except that proposals for Calibration Programmes do not require any keywords. The keywords must be selected in decreasing order of relevance (i.e., the first selected keyword is the most relevant).

Proposal anonymisation:

The proposal anonymisation is mandatory. Failure to abide by the Dual-Anonymous Peer Review (DAPR) rules may lead to the disqualification of the proposal. Applicants must formulate the scientific rationales of their proposals following the anonymisation rules and examples described in this link, which also gives a detailed description of the DAPR paradigm.

The fields Background and Expertise and Data Product Delivery Plan (in the case of Large Programmes) are the only fields of the proposal in which information on the proposing team can be disclosed. These fields will not be included in the material distributed to the referees during the proposal review phase and will only be accessible to them after the ranking phase is completed.

Large Programs:

Large Programmes, those that require 100 hours or more, are not accepted for Period 113. Large Programmes can only be submitted in even Periods, i.e., Periods with the proposal submission deadline in March/April. A number of instrument restrictions for Large or Monitoring Programs apply. We refer the reader to Sect. 4.4 in the Call for Proposals Period 112.

Any-weather programmes:

In the interest of maximizing scheduling flexibility and accommodating the often over- and under-subscribed observing conditions, applicants for observing time are strongly urged
to consider essential information provided on our designated webpages: Forecast of telescope pressure, and Any-weather programme statistics. This information can guide your selections and enhance the likelihood of fulfilling your observing objectives. Please take particular note of the current high demand on UT4, especially in the 9<RA<14h range, where securing observing time will be notably challenging.

Rapid Response Mode (RRM) activation policy:

The RRM policy changed starting in Period 105: on-going observations on any VLT instrument can be interrupted by an RRM triggered on that specific UT, even if the trigger requires a change of focus, unless the relevant programme is specifically protected against an RRM trigger (in case of strictly time-critical programmes). The change has been implemented at all UTs. More information on the Rapid Response Mode can be found on the Phase 2 page.

UT instruments and facilities

UT1 - Antu

  • KMOS:
    • KMOS, is fully operational since October 2021.
    • Since P112, the observatory only provides a telluric in twilight observed at an average airmass. Users must take this into account and provide their own tellurics concatenated to the OBs if a maximum difference of airmass or time is required by their science goals.

UT2 - Kueyen

  • UVES:
    • With the purpose of producing up-to-date response curves in all offered standard setting, starting from the beginning of P111 flux standards will be taken with bi-weekly cadence in the modes DIC1 346+580, 390+564 and DIC2 437+860, and with monthly cadence in the setting DIC2 390+760 and RED 520, 600.

UT3 - Melipal

    • For the star center observations (obs. Type=C), the WAFFLE pattern amplitude in all modes is calculated automatically and should be left as “AUTO” by default.
    • The IFU mode of XSHOOTER has been decommissioned and is not available anymore.

UT4 - Yepun

  • MUSE:
    • The extension of the GALACSI NFM tip-tilt limiting J-band magnitude has been commissioned. Details are available on the news page of MUSE.
  • ERIS:
    • The instrument is currently still under commissioning and will be offered in selected modes only in Period 111. The instrument consists of an integral field spectrograph (IFS) and an imaging camera (NIX). The IFS provides medium-resolution (R ~5000 to 10000) spectroscopy in the near-infrared  over a 1-8 arcsecond field of view and, with either natural guide star (NGS) or  laser guide star (LGS) supported adaptive optics, or in seeing-limited mode. NIX provides diffraction-limited imaging over either a 30 or 60 arcsecond field of view, between the J and M-bands, also with either  NGS or LGS supported adaptive optics, or in seeing-limited mode. NIX can also be used in conjunction with an apodising phase plate coronagraph for high-contrast imaging.
    • Several additional new modes and functionalities will be offered in P112. The bright magnitude limit for NGS has been removed, and the faint magnitude limit for LGS tip-tilt stars has been relaxed from RP=17 to RP=18. Seeing-enhancer mode is offered for targets without suitable tip-tilt stars. Non-sidereal and differential tracking modes are also offered. For NIX, the three sparse aperture masks are now offered, as well as detector windowing with four preset subarrays.
    • The focal plane coronagraphy (FPC) and long-slit spectroscopy (LSS) modes for ERIS will be offered in P113.

Incoherent combined focus

    • A new public version of the ESPRESSO pipeline was recently released (version 2.4.0). This new
      pipeline version include a fix to detect Fabry Perot peaks in the HR42, which were affected by an intervention.
    • The ESPRESSO LFC has been fully operational since October 2022, and the LFC calibrations for different modes have been included in the daily calibration plan. However, a detailed analysis of the LFC data collected between October 2022 and May 2023, by the ESPRESSO IOT, has revealed a strong degradation in the LFC performance. A maintenance is scheduled for Oct/Nov. 2023 aimed at improving the LFC current performance. The LFC status and performance will be updated in the ESPRESSO news webpage and in the user manual.

Visitor focus

  • The UT1 Nasmyth A focus is available for Visitor Instruments, but the installation of the field corrector lens for MOONS may impose limitations.
  • Potential users of a visitor focus are requested to consult the VLT Visitor Instruments page.

VLTI instruments and facilities


  • For new users to VLTI needing assistance to prepare their VLTI proposals, the community supported VLTI Expertise Centres - disseminated throughout Europe - can offer in-depth support. They also offer support for advanced data reduction and interpretation.
  • Monitoring and Large Programme proposals on the VLTI-ATs are accepted for both GRAVITY and for MATISSE for all modes except the HIGH+ spectral setting and the GRA4MAT mode. Such programmes on the VLTI-UTs will only be available again after the arrival of GPAO.



  • VLTI-UT (MACAO and CIAO) operation will cease after the July 2024 UT run for the GPAO implementation to begin.


  • ESO will continue a scheme to optimise operations for aperture synthesis with the VLTI. This scheme only applies to service mode proposals using ATs with PIONIER, GRAVITY and MATISSE. The reader is referred to the Period 113 VLTI manual for further details.
  • In P112, we introduced the extended configuration A0-B5-J2-J6, offering the longest baselines on the VLTI platform. It is offered for single-field operations. Due to the redundancy with the astrometric configuation, the previous large configuration A0-G1-J2-J3 is no longer offered.


  • One VLTI visitor focus (VISITOR 1) is available. Potential users are requested to consult the VLTI Visitor Instrument page.
  • GRAVITY is offered on all AT configurations as well as on all four UTs with the visible (MACAO) and infrared (CIAO, off-axis only) adaptive optics system in Service and Visitor modes.
    • The on-axis mode of the IR wavefront sensor CIAO cannot be offered for the time being due to critical problems that were identified during its commissioning.
    • ESO invites proposals with the goal of performing astrometric measurements (see, e.g., the following articles: Gravity collaboration, 2017 A&A 602, A94 and The Messenger 170, 10). Proposers who need help with the preparation of GRAVITY astrometric observations are invited to contact the ESO Helpdesk well in advance of the deadline.
    • Starting with P110 GRAVITY a new observing mode dual-field wide is offered for the UTs and the small & large configurations of the ATs. This mode allows fringe tracking from a target that is up to 30 arcsec away from the science target by using the VLTI Star Separators to separate the beams. The magnitude limits of the fringe tracker and acquisition camera and the expected sensitivity for the science camera in this mode can be found on the GRAVITY webpage and are based on a preliminary characterisation of the mode. Due to the need of good atmospheric conditions (turbulence class 30% and better), observations are strongly encouraged to be carried out in service mode to ensure that the conditions are met. Note that 'dual-field wide' mode only provides relative measures (differential visibilities and phases), no absolute visibilities, due to atmospheric effects when separation increases. Calibrations of the interferometric transfer function are thus not needed and not offered for this mode.
    • Starting with period P112 GRAVITY single-field and dual-field acquisition templates will each be split into two separate templates: on-axis and off-axis. More information on their use cases can be found in the GRAVITY User Manual.
  • MATISSE is offered on the UTs (supported by the visible MACAO AO system) and on the short, medium and large AT configurations in Service and Visitor modes.For \href{}{\bf\underline{MATISSE}} targets for which photometry may be too noisy, direct measurement of the {\bf correlated fluxes} is possible for objects with lower fluxes that for visibility measurements. See the \href{}{\bf\underline{MATISSE news page}} for details. Absolute calibration of correlated fluxes requires special calibrators, as not only their sizes need to be known, but also their SED. Please contact the \href{}{\bf\underline{VLTI Expertise Centre at Leiden Observatory}} for help with selecting appropriate calibrators and data reduction.
    • MATISSE is available with the GRA4MAT mode with ATs fully, and only without chopping for UTs.
    • The instrument offers the choice of various spectral resolving powers covering either L and/or M-band (depending on the resolving power) and N-band. The HIGH+ mode is only available with the GRA4MAT mode.
    • Monitoring programmes are offered in all settings in Period 111, except for the new HIGH+ spectral setting. Additionally, Large or Monitoring Programmes requesting the GRA4MAT mode will not be accepted.
    • For targets for which photometry may be too noisy, direct measurement of the correlated fluxes is possible for objects with lower fluxes that for visibility measurements. See the MATISSE news page for details. Absolute calibration of correlated fluxes requires special calibrators, as not only their sizes need to be known, but also their SED. Please contact the VLTI Expertise Centre at Leiden Observatory for help with selecting appropriate calibrators and data reduction.
    • As from P112, MATISSE is offered for narrow off-axis mode for exo-planet and similar observations (with GRAVITY as fringe tracker), meaning while GRAVITY tracks fringes on a source, MATISSE can point to a nearby offset position. See the MATISSE news page for details.
  • PIONIER is offered on all ATs configuration and UTs + MACAO in both service and visitor mode. The limiting magnitudes of PIONIER have been updated following the improvements thanks to the installation of NAOMI. The execution times have been adapted accordingly. See the overview or overheads pages.
    • The cooling pump of the detector is currently not performing, which affects the performance of the instrument. ESO, in collaboration with the PIONIER consortium, is looking into possible solutions. A direct consequence of the instrument status is that no Large nor Monitoring Programs are offered since Period 112.