GRAVITY+ Adadaptive optics (GPAO) with Laser Guide Stars (LGS)

As part of the GRAVITY+ project, the Adaptive Optics for UT1,2,3 and 4 feeding the VLTI have been upgraded to bring higher strehl and more stable images, improving greatly the sensitivity and performance of VLTI instruments. The MACAO systems have been retired. In 2025, ESO and the GRAVITY+ consortium are installing laser guide stars to improve the sensitivity of the AO system up to Grp=17 (Gaia red magnitude). Under the best 10% atmospheric conditions, the limiting magnitude of the GRAVITY fringe tracker reaches K=12.5 on-axis, and K=13.0 off-axis.

The commissioning of the VLTI with GPAO+LGS will occur between October and December 2025, and will be followed by Science Verification in early 2026:

• The GPAO+LGS SV will follow the VLT/I Science Verification Policy and Procedure
• The equivalent of four nights (~40 hours) has been set aside for SV, to be executed in service mode between January 2026 and April 2026
• Raw data will be made public immediatly

Timeline

• Opening of the call: July 7th 2025
• deadline for proposal submitted on ESO phase1: August 12th 2025, 12:00 CEST (noon) (make sure you submit your proposal in the GPAO-LGS cycle!)
• Proposals selection results: mid-September 2025
• Phase 2: TBD
• Observations: between January and April 2026, in service mode. Please consult the LPO schedule for the dates of the VLTI runs.

GTO protected targets

The list of protected targets for the GRAVITY and MATISSE Guaranteed Time Observations is available for P116 and P117 (to be announced early August). Note that both lists will apply when selecting SV targets. Observations of targets protected by GTO will not be accepted for SV.

The observations will be conducted in Service Mode by a dedicated team of ESO astronomers and in close collaboration with the GRAVITY+ team. The GPAO+LGS SV team will be able to assist the successful PI¹s in the preparation and optimisation of the OBs on a best effort basis only. The collected data will be made available to the whole ESO user community.

WARNING: all (raw) data and calibrations are public immediately after the observations. There is no proprietary period nor earlier data release to the PIs. See the VLT Science Verification Policy and Procedures for more details.

Offered modes

All GRAVITY and MATISSE (including GRA4MAT) modes are offered. Please refer to the respective web pages and documentation: GRAVITY and MATISSE.  

Observing Time and limiting magnitudes

The conservative estimation of a CAL/SCI sequence is one hour. This duration should be taken as the basis in your proposal preparation (see GRAVITY and MATISSE documentation). In order to offer a fare share of the science verification time we recommend the submission of programs that do not request more than 1 night (10 hours) of cumulated time (i.e. 10 CAL-SCI containers). Any proposal requesting more should have a strong scientific justification.

Limiting magnitude for the Tip-Tilt star aka NGS star

While the laser guide star is used to measure the high order atmospheric aberations, a natural star is still required to correct the Tip-Tilt. This star (NGS star) is observed either in the visible (LGS-VIS) or in the infrared (LGS-IR).  

Note that at the limiting magnitude and/or off-axis, the performance are degraded: nominal performances are only reached for 2mag brighter and on-axis. E.g., in LGS-VIS on-axis at Grp=15 reach nominal strehl at a maximum separation of 5". The off-axis NGS star can be selected up to 30" away.  

GRAVITY limiting magnitude as function of turbulence categories 

Note that the SC limiting magnitude reached for 1h on target. A calibrator+science sequence (CAL-SCI container) lasts 60min (30min+30min), with only 20min spent on sky on the science target. In other words, 3 containers CAL-SCI are required to reach the SC limiting magnitude.   

"sep" refers to the separation between the SC and FT objects on sky.

MATISSE sensitivity, including GRA4MAT limiting magnitudes

MATISSE sensitivity is the same as offered for P116. The limiting magnitudes (as function of turbulence categories) for the GRAVITY fringe tracker in the GRA4MAT mode are updated as follow:

Contact

for additional information, please send us an email.