Important recent changes regarding La Silla, Paranal and APEX instrumentation and facilities

This section describes important changes which took place during Period 103 and 104, as well as changes expected to take place during Period 105.

p1: A new tool for proposal preparation and submission:

A new tool for the preparation and submission of observing proposals is deployed in Period 105. This represents the first part of a broader re-haul of the ESO Phase 1 system (p1) that also entails a significant modernisation of the Observing Programmes Committee, refereeing process, and related tools. The new p1 system is web-based, resembles the recent p2 tool. Users are encouraged to get familiarised with the new system using the p1demo tool well before the proposal deadline.

Large Programs:

Starting in Period 104, Large Programmes are only offered in even Periods, i.e., Periods with proposal submission deadline in March/April.

La Silla

Instruments and Facilities

  • NIRPS:  the Front End Adaptive Optics and the Back End of the Near Infra-Red Planet  Searcher are expected  to  be  commissioned at  the  3.6-m telescope in the fourth quarter of 2019 and the 2nd/3rd quarter of 2020, respectively. The installation of NIRPS is not expected to affect the operations of HARPS in Period 105.
  • SoFI and EFOSC2:  Monitoring Programmes with SOFI and EFOSC2 are not offered in Period 105, as the installation and commissioning of SoXS - the Son of X-Shooter - is expected to start during the first quarter of 2021.
    • 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 105. 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 105 GTO target protection webpages.




Proposals for exceptional weather conditions:

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 field of the p1 proposal preparation tool. Users requiring excellent seeing conditions should apply for the 10% best turbulence conditions following the new handling of atmospheric constraints. The proposals should describe why the science can only be achieved in such conditions.

Target of Opportunity observations:

The implementation of the p2 system has lead to a change in the procedure for triggering Target of Opportunity observations since Period 103. Successful proposers of ToO runs still have to prepare (usually dummy) OBs for their observations well ahead of the beginning of an observing Period. However, before triggering the ToO, the PI of the programme (or one of his/her delegates) will now use p2 to directly update the OB with the relevant coordinates and exposure times, insert configuration files if necessary, and attach a finding chart. The service observer will then execute the specified OB.

If real time assessment of the observations can be beneficial for their scientific output, the Paranal Observatory Eavesdropping Mode can be requested at the time of the trigger; it will then be activated by the service observer at the start of the execution of the OB.

Further details will be available on the Phase 2 Target of Opportunity Procedures webpage.

Note that Rapid Response Mode observations are executed following a different procedure; in particular, it does not involve p2 at the time of the trigger (see the Phase 2 Rapid Response Mode Procedures webpage).

Visitor and service mode observations in any UT2 instrument can be affected by Rapid Response Mode (RRM) trigger

In Period 105, pending successful commissioning, the RRM policy will be subject to a change. Starting with UT2, it is foreseen that any observation can be interrupted by an RRM trigger, even if the trigger requires a change of focus, unless the relevant program is specifically protected against an RRM (in case of strictly time-critical programmes). This capability is foreseen to be extended to the other UTs in Period 106.


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

  • KMOS:
    • Since the beginning of May 2019, Arm #14 shows an hard point in the linear driver. It is thus parked and in simulation. KMOS is available for Science Operations with 23 arms. An intervention might possibly be planned beginning of Period 105.

UT2 - Kueyen

  • XSHOOTER: the calibration plan does not include observations of telluric standard stars. Please refer to the User Manual regarding the correction of telluric lines.

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,  turbulence category for SPHERE proposals must be better than 85%, or smaller for targets which cannot be observed at low airmass.
    • Since Period 103,
      • a new acquisition template (to be used in the second or later OB of a concatenation) allows one to alternate Adaptive Optics (AO) observations on two stars of similar magnitudes (delta mag < 2) and separation < 30 arcminutes, with only one minute gap between integration sequences, by eliminating the need to repeat the AO acquisition;
      • the constraint on the Atmospheric Turbulence Model for Phase 2 OB preparation now combines constraints on coherence time and seeing. The combinations of values correspond to excellent, good, median and poor conditions and better match the expected SPHERE performance. The ETC has been updated accordingly.
  • VISIR will be moved back from UT4 to UT3 likely during the second half of Period 104 (see below). On UT3, VISIR is offered with all functionalities.
  • Following its upgrade into a cross-dispersed spectrograph, CRIRES will be installed on the UT3-Melipal Nasmyth B focus in Period 104. Its commissioning will take place in Period 104 and possibly in Period 105.

UT4 - Yepun

  • HAWK-I :
    • Monitoring Programme as well as Target of Opportunity proposals are accepted for both HAWK-I in NoAo and in AO mode with GRAAL in Period 105.
  • MUSE
    • The combination of the  Ground Atmospheric Layer Adaptive Corrector for Spectroscopic Imaging (GALACSI) in its Laser Tomographic Adaptive Optics (LTAO) mode with MUSE in Narrow Field Mode (MUSE-NFM AO mode) has been offered since Period 103.
    • Monitoring programmes for MUSE are accepted in MUSE-WFM NoAO and MUSE-WFM AO modes. But they are not accepted in MUSE-NFM AO mode, as its characterisation must be improved.
    • Target of Opportunity proposals are offered for MUSE in all modes.

Incoherent combined focus

    • The 1-UT mode has been o ffered since Period 102. ESPRESSO OBs for the 1-UT mode can be executed from any UT. Two observing modes are available:
      • (1) the High Resolution (HR) mode providing a resolving power of 140 000, and
      • (2) the Ultra High Resolution mode (UHR), providing a resolving powerof 190 000.
    • The 4-UT mode is offered since Period 103.
      • It provides a medium resolving power (MR) of 70 000.
      • It is offered in in Visitor Mode only. Observations will be scheduled in groups of consecutive nights. Users must request a total time that is an integer multiple of half-nights (corresponding to 5 hours in Period 105), with a minimum duration for each individual observing slot of one half-night.
      • Proposals requesting ESPRESSO in 4-UT mode must in particular justify its use compared to the 1-UT mode.
      • Monitoring Proposals for ESPRESSO in 4-UT mode are not accepted.
    • The instrument underwent a successful intervention in July 2019, leading to an increase of troughput. In the blue arm, the gain is of up to 60% and in the red arm the gain is of up to 40%. When averaged over the whole wavelength range of ESPRESSO, the gain in troughput is of at least 30%. Werefer the users to the ETC for an updated estimation of the instrument throughput.

Visitor focus

  • The UT1 Nasmyth A focus is available for Visitor Instruments since mid-November 2019.
  • The UT4 Cassegrain focus is available for Visitor instruments for the early months of P105.
  • 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.
  • 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.
  • Monitoring Programme proposals on the VLTI-UTs and VLTI-ATs are accepted for GRAVITY, MATISSE, and PIONIER in Period 105.
  • Since Period 104, for each observing run, one or more of the following observation types (snapshot, time series, imaging and astrometry) which best describe the proposed observations shall be specified in the instrument configuration section of the proposal. See the VLTI user manual for more details.


  • Since Period 104, AT configurations will be requested by generic names ("small", "medium", "large" and "astrometric") rather than explicit configurations. The standard configurations used for a given period are detailed on the VLTI configuration web page and should be used for phase1 and phase2 preparation. For operational reasons, observations may take place (although rarely) on “relocation configurations” which occur the nights during a transition between two standard configurations. A criteria of at least 50% baseline length overlap will be used. This scheme will be primarily used for imaging programmes. The overlap in baseline length between standard and relocation configurations is detailed on the aforementioned web page.
  • In Period 105, 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 105 VLTI manual for further details.


  • The VLTI visitor focus is available from P105. Potential users are requested to consult the VLTI Visitor Instruments page.
  • GRAVITY is offered on all AT configurations as well as on all four UTs with the visible (MACAO) and infrared (CIAO) adaptive optics system (both on-axis and off-axis) in Service and Visitor modes.
    • GRAVITY will undergo an intervention in October 2019 to replace the medium and high resolution grisms of the science combiner; a sensitivity increase by a factor of two is expected for these two settings of the science combiner.
    • The limiting magnitudes for the ATs have been increased by 1 magnitude due to NAOMI, since P104.
    • 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). 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.
  • MATISSE, the Multi AperTure mid-Infrared SpectroScopic Experiment is a second generation instrument operating on the VLT interferometer in the L (3-4μm), M (4.6-5μm) and N (8-13μm) bands. MATISSE maximum angular resolution is 3.5 mas in the L-band and 8 mas in the N-band with the longest AT baseline. On the UTs, the angular resolution is 5 mas in L-band, and 12.5 mas in N-band. Its commissioning started in Period 100 and will continue in Period 105.
    • MATISSE offeres the choice of various spectral resolving powers:
      • Low (R=34) covering both the L and M bands (for which the choice of DIT affects the sensitivity in one or the other band)
      • Medium (R=506) covering either the L or the M band depending on the central wavelength
      • High (R=959) covering the L band only
      • The N-band resolving power is either Low (R=30) or High (R=218)
    • The instrument is offered with either four UTs (with MACAO only) or four ATs in standard VLTI configurations, providing six visibilities and four closure phases in one observation.
    • MATISSE is offered in Service and Visitor modes.
    • Monitoring programmes for MATISSE are offered in Period 105, except in the M-band.
    • Various technical activities will take place during Period 105:
      • intervention on the cryo-cooling system
      • replacement of the Very High Resolution grating
  • 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 due to NAOMI installation. Finally the execution times have been adapted to the target brightness. See the overview or overheads pages.

Survey telescopes and instruments


  • The seven second generation VISTA Public Surveys are all in full operation and most are expected to finish towards the end of Period 104, the remaining running into P106. This means significantly large amounts of telescope time (>~500 hrs) will become available for normal programmes, and ESO encourages the submission of normal proposals for VISTA making use of the full allowed range for the total requested time, i.e., up to 99 hours.
  • All observing time is available in Period 105 within the full range of atmospheric conditions. Particularly encouraged are open time proposals requesting any weather conditions (THIN and turbulence category 85% or 100%). No restrictions regarding the RA range are implied.
  • Monitoring Programmes are accepted in Period 105.  PIs of Monitoring Programmes should consider that such programmes can run at most over 3 semesters as Period 107 is expected to be the last period of VIRCAM operations, due to the start of modifications of VISTA for the installation of 4MOST. Proposals that waive proprietary rights are encouraged.


  • Normal and Monitoring proposals are accepted on the VST in Period 105 without restriction on the conditions.  PIs of Monitoring Programmes should consider that such programmes can run at most over 3 semesters as the contract between INAF and ESO ends at the end of Period 107. Proposals that waive proprietary rights are encouraged.




APEX upgrade:

The upgrade of the APEX telescope was completed in April 2018. It consisted of:

  • the replacement of the M1 surface panels with panels of higher accuracy, optimizing the telescope efficiency for high frequencies;
  • the replacement of the entire secondary unit with a new wobbler, allowing to switch between on and off positions separated by up to 10' at a rate of up to 2 Hz;
  • new telescope drives;
  • a new shutter mechanism.

In parallel, a new set of facility instruments is being installed (SEPIA and nFLASH), which replace the decommissioned SHFI.

Dates for ESO observing time:

The dates for the ESO observing time in Period 105 are expected to be in late March, May and July 2020. Time critical observations should only be requested within these time slots. Users are encouraged to check the latest version of the schedule.

ESO share in the APEX collaboration:

The ESO share in the APEX collaboration has increased from 27% to 32%. The exact distribution of the observing time between the APEX partners can be found on the APEX web pages.

Length of normal programmes:

In order to solicit longer normal programmes for observations that do not require the best weather conditions, the maximum length of normal programmes on the instrument PI230 has been raised to 199 hours. For any other instrument, the limit remains 99 hours. Any PI230 programmes requiring 200 hours or more should also be requested as Large Programmes.

Monitoring programmes:

Monitoring programmes will only be accepted for ARTEMIS and SEPIA (SEPIA-180 and SEPIA-660).