HAWK-I/GRAAL Science Verification


General Information

An integral part of the commissioning of a new instrument at the VLT is the Science Verification phase. SV programmes include a set of typical scientific observations that should verify and demonstrate to the community the capabilities of the new instrument in the operational framework of the VLT Observatory. In accordance with its SV Policy and Procedures  ESO encourages the community to submit also highly challenging or risky science observations that will push HAWK-I/GRAAL and the VLT to its limits in order to better understand the performance parameter space and its envelope. Such observations should focus on the instruments core modes in order to benefit a wide community.

HAWK-I is a cryogenic wide-field imager installed at the Nasmyth A focus of UT4. The on-sky field of view is 7.5'x7.5', with a cross-shaped gap of 15" between the four detectors. The pixel scale is of 0.106".  The instrument is offered with 10 observing filters placed in two filter wheels: 4 broad band filters (Y, J, H & K) and 6 narrow band filters (Br𝛾, CH4, H2, 1.061 μm, 1.187 μm & 2.090 μm).

In combination with GRAAL (the ground layer adaptive optics module of the VLT Adaptive Optics Facility) HAWK-I will offer a significantly improved image quality. GRAAL is able to compensate for the lowest layers of the atmospheric turbulence (up to ~ 300-500 m, depending on the spatial frequencies considered), carrying more than half of the turbulence variance.

The HAWK-I+GRAAL seeing enhanced mode is expected to provide:

  • deeper expositions for nearly point-source objects, or
  • deeper detection limiting magnitude
  • the operation of HAWK-I for more than 80% of the time with an equivalent K-band seeing of 0.55" (instead of 0.7" without GRAAL)
  • excellent image quality in good atmospheric conditions (0.3” for around 30% of the time).

The adaptive-optics assisted HAWK-I mode is now offered to the community for Science Verification (SV) for 4 nights in January 2018. All astronomers are invited to participate in this opportunity to obtain unique science with the HAWK-I AO-supported mode and thus to demonstrate its scientific capabilities. A call for proposals has been issued and the community is invited to submit proposals for the HAWK-I/GRAAL science verification using the simplified proposal template.

The deadline for proposal submission is 31 October 2017, 18:00 CET.

Proposals will be reviewed by an internal panel and allocated time on the basis of scientific merit and feasibility, as well as in the demonstrated ability of the Principle Investigators to deliver results on a timely basis.

The observations will be conducted during the nights of 2-5 January 2018 in Service Mode by a dedicated team of ESO astronomers. The HAWK-I/GRAAL SV team will be able to assist the successful PI’s in the preparation and optimisation of the OBs.

The HAWK-I ETC has not been updated for the new mode yet, as the commissioning is still pending. We encourage the proposers to use the current HAWK-I ETC with a slightly increased (i.e. better) image quality for the calculation of the exposure times.

The latest version of the HAWK-I data reduction pipeline will be available for reduction of the SV data. Proposers are reminded that all SV data are made public worldwide immediately after passing the usual quality control checks.

Short description of HAWK-I/GRAAL

GRAAL is based on the 4 sodium Laser Guide-Stars system of the VLT. The lasers are pointed towards areas located outside of the science field of view (7.5 arcmin), and the light re-emitted by the 80-100 km altitude Sodium layer is collected by 4 WFS (wavefront sensors) each with 40x40 subapertures. The slopes provided by the WFS are combined to provide an estimate of the WFE for the lowest layers; this shape is then removed from the actual shape of the DSM. The AO-loop is closed at a 700 to 1000 Hz frequency.

As the LGS are not useful to sense tip-tilt, an additional visible Natural guide-star WFS is embedded in GRAAL, and the tip-tilt is corrected at a loop frequency of 250 Hz. The science HAWAII 2RG infrared sensors of HAWK-I will as well be used to correct slow drifts between visible wavefront sensing and IR imaging paths, coming from flexures and uncompensated atmospheric dispersion, taking the opportunity of continuous reading of the science detectors during integration.


HAWK-I/GRAAL observations are supposed to make use of a bright nearby star to sense the tip-tilt of the wavefront. The tip-tilt star (TTS) should have a R-magnitude in the range 6-16.5 mag, and must be located at 8.2'+/-0.5' radial distance from the HAWK-I science target (see figure below).  The magnitude of the TT star must be indicated in the SV proposal. In case there is no suitable TTS, the observations can be carried out in TTS-free mode by using only the 4 LGS. This mode still provides good correction, with performances that are only few percents lower than the full AO mode (i.e. TTS and 4LGS).

Left: GRAAL focal plane illustration. The 4 LGS rotate with respect to the FoV. The visible TT-star is selected outside of the LGS ring. Right: GRAAL expected performance.

Approved programmes

A total of 14 proposals have been allocated SV time. The observations were performed in Service Mode style by a dedicated team and the collected data is made available to the whole user community through the ESO Archive. See VLT SV Policy and Procedures for more details.

WARNING: Due to a commissioning delay the observations were carried out in Tip-Tilt Star - free (TTS-free) mode, which uses only the 4 lasers. This means  SV users do not have to indicate a TT-star in their OBs! Because no TT star is used and the lasers by design always follow the target, this mode implies a 100% of sky coverage. As stated above the expected perfomance is not significantly impacted by the lack of TT correction.

All (raw) data and calibrations for the respective programmes can be accessed by following the link in the STATUS column in the table below.
There is no proprietary period nor earlier data release to the PIs.


Programme ID
PI Name
Project Title Status
60.A-9466(A) Bouy Probing the core of nearby clusters
60.A-9467(A) Dalessandro Looking for blood ties: the true nature of cluster pairs in the Large Magellanic Cloud COMPLETED
60.A-9468(A) Opitom Assessing the infrared photometric variability of the dwarf planet Eris and its moon Dysnomia
60.A-9469(A) Zivkov Probing the effects of low-metallicity on young stellar evolution
60.A-9470(A) Muzic Embedded clusters as laboratories for star formation COMPLETED
60.A-9471(A) Husemann Resolving the host galaxies of a close dual AGN candidate system at z = 3.3 COMPLETED
60.A-9472(A) Schneider How symmetric is a symmetric outflow? A deep H2 image of the Herbig Haro object 212
60.A-9473(A) Schrabback Demonstrating the power of HAWK-I+GRAAL for deep weak lensing measurements of high-redshift galaxy clusters
60.A-9474(A) Wylezalek HAWKI/GRAAL study of the galaxy cluster CARLA J1129+0951 PARTLY EXECUTED
60.A-9475(A) Kankare HAWK-I/GRAAL imaging of four nearby luminous infrared galaxies PARTLY EXECUTED
60.A-9476(A) Rejkuba Resolved stellar populations in a dwarf galaxy in the Centaurus A group PARTLY EXECUTED
60.A-9477(A) Nonino Commissioning nature's largest, high-resolution, wide-field, cosmic telescope NOT STARTED
60.A-9478(A) Heydari-Malayeri Probing the nature of a rare, compact HII region in the LMC
60.A-9479(A) Rouan Detailed studies of Super Stellar Clusters in LIRGs galaxies

Phase2 preparation

The PIs (or their Phase 2 delegates) of accepted proposals must prepare and submit the Phase 2 material using P2PP3 

by 14 December 2017, 12:00 Central European Time (CET)

to ensure that all observing material can be verified and is ready for the observations during the SV run between the 2nd and 5th of January, 2018. Users are encouraged to use an SV-dedicated new release of the GuideCam tool (see checklist below), which helps preparing OBs, as well as creating ESO compliant finding charts. The GuideCam tool will send OB acquisition parameters and the Finding Chart(s) directly to the selected OB in P2PP3 (i.e. P2PP3 must be running and a HAWK-I OB with an AOF acquisition template be selected)

Here we provide a quick checklist that will guide you through the preparation of the Phase 2 package for your upcoming HAWK-I/GRAAL SV observations.

Before you start...:

  • Download and install P2PP version 3.4.3 (P2PP3)
  • Check that you know your ESO User Portal username and password as you need them to log into P2PP and prepare the OBs. Please consult the User Portal FAQ for more information.
  • Consult the short tutorial describing the requirements for the preparation of HAWK-I/GRAAL TTS-free mode OBs.
  • Download and install the latest version of the SV-dedicated GuideCam tool (version for MacOSX or the version for Linux)
  • Consult the short GuideCam video tutorial for HAWK-I/GRAAL observations in TTS-free mode.

The Phase 2 package consists of...:

  • A set of OBs, constructed and submitted to the ESO database using P2PP3. 
  • Finding charts that are attached to OBs either with P2PP3 or by the GuideCam Tool (FCs are automatically submitted when the OBs are checked-in).
  • A README file providing an overview of your programme details, also prepared and submitted from within P2PP3

Once the submission is complete..:

  • Do not forget to click the Alert ESO... button (the whistle button in the tool bar) in P2PP3! This step has to be repeated for every observing run for which you are submitting Phase 2 material. Please be reminded that your phase 2 package submission, re-submission, or modification will not be processed until you have notified ESO of the completion of your submission using the Alert ESO... button.

Where to seek help...:

  • Please contact the ESO User Support Department in all matters regarding phase 2 preparation. Please include the programme ID in the subject line!

Data Access and Pipeline

Interested users can access the SV frames (raw science only) by clicking on the STATUS info listed in the table above.

A HAWK-I pipeline is available for data reduction here, together with installation instructions and pipeline manual.

NOTE: To process SV data with the ESO Reflex workflow and the pipeline v2.4.2 you must disable the interactivity in the science actor.


Useful links