Important recent changes regarding La Silla and Paranal instrumentation and facilities

This section describes important changes which took place during Periods 110, as well as changes expected to take place during Periods 111 and 112.

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 111, 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:

Period 108 marked the full deployment of the Dual-Anonymous Peer Review (DAPR) for proposals submitted to this Call. 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. While Period 106 was used as a dry run, both to make the community aware of the upcoming implementation of DAPR and to test its practical, procedural and policy aspects, from Period 108 proposal anonymisation is mandatory. Failure to abide by the DAPR rules may be penalised.

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 111. 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.

La Silla

Instruments and Facilities

  • NIRPS is currently still under commissioning and is not yet fully characterised, but will be offered as of Period 111. NIRPS
     is a near-infrared (971nm-1854nmm), high-resolution (up to R = 84 000), cross-dispersed (70 orders) fibre-fed spectrograph optimised for stability and designed for the detection and characterisation of exo-planets around late-type stars. It can be used simultaneously with HARPS to collect spectra from 380nm to 1854nm (with a gap from 689nm to 971nm) in a single acquisition. Its ultimate goal is to reach a long-term stability of ~1 m/s, but for the first period a more conservative value of 3 m/s is adopted. A Laser Frequency Comb for wavelength calibrations is expected to improve further the stability from period 112 onwards.
  • HARPS can be operated simultaneously with NIRPS starting from period 111.
  • The Visitor (Cassegrain) focus of the 3.6-m telescope is not offered during Period 112 due to the operation of NIRPS. The possibility of offering this visitor focus will be re-evaluated in the future.
  • The Visitor focus of the NTT continues to be available during P112.
  • The installation and commissioning of SoXS - the Son of X-Shooter - are expected to start in Period 112. As a consequence, SoFI has been decommissioned, and EFOSC2 is expected to be decommissioned during Period 112.
  • The multi-object spectroscopic (MOS) mode of EFOSC2 has been decommissioned in Period 111.
    • ULTRACAM is a high-speed imaging photometer designed to study faint astronomical objects at high temporal resolutions. ULTRACAM employs two dichroic beamsplitters and three frame-transfer CCD cameras to provide optical imaging with a field-of-view of 60 and at frame rates of up to 300 Hz simultaneously in the u'g'r', u'g'i' or u'g'z' bands.
    • This PI instrument is o ffered to the ESO community for up to 5% of the observing time at the NTT in Period 109. Large Programmes will not be accepted.
    • Operation of this PI instrument requires the presence of the instrument team, so ULTRACAM programmes will preferentially be scheduled contiguously on periods of several nights. For questions on the instrument and observation strategies, users shall contact the instrument PI, Prof. Vik Dhillon (vik.dhillon[AT], at least two weeks prior to submitting their proposal.
    • The ULTRACAM consortium is committed to support the PIs and observers from the ESO community that have been awarded telescope time with ULTRACAM. The ULTRACAM team will support the execution of the observations and the subsequent data reduction to allow the scienti c exploitation of the data obtained with ULTRACAM.
    • Proposers must check that their planned observations do not duplicate any protected targets speci fied for ULTRACAM in the Period 112 GTO target protection webpages.




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


  • FORS:
    • FORS1, the upgraded FORS instrument, is expected to be installed and see first commissioning in P114. FORS2 will thus be decommissioned in P114,    and first commissioning of FORS1 without the MXU is planned to occur in P114. FORS1 will be retrofit with the MXU, and further commissioning will be achieved in P115. Therefore, the MXU mode will not be available for several months between P114 and P115.
  • KMOS:
    • KMOS, is fully operational since October 2021.
    • Starting from period P112, the observatory will only provide 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.

Incoherent combined focus

    • There was a major instrument intervention between May 1-16, 2022. Further details will be given in the next version of the ESPERSSO User Manual.
    • 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 the intervetion.
    • The Laser Frequent Comb (LFC) is now fully operational and proposals requesting it for wavelength calibration will be accepted. User will still need to clearly indicate the need for the LFC for their science.

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-UTs and VLTI-ATs are accepted for both GRAVITY and PIONIER without restrictions, and for MATISSE for all modes except the HIGH+ spectral setting and the GRA4MAT mode.


  • 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 111 VLTI manual for further details.
  • From P112, we introduce 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 current large configuration A0-G1-J2-J3 will no longer be offered. The current astrometric configuration is renamed "large".


  • Two VLTI visitor foci are 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 for Period\,112.