P104:

As of P104, AT configurations will be requested by generic names ("small", "medium", "large" and "astrometric") rather than explicit configurations using AT positions. The following table shows which instrument / mode can request which configuration. By clicking on their name, the user can see the sky coverage corresponding to the standard AT positions for a given configuration.

Note: the standard astrometric configuration, A0-G1-J2-K0, is a variation of the standard large configuration A0-G1-J2-J3. It has all its telescopes south of the delay line tunnel, which is mandatory for GRAVITY dual-feed observations.  

This new scheme allows a more flexible execution of OBs, for example using intermediate configurations during AT relocations (transition nights between two standard configurations). This scheme will be primarily used for imaging programmes.  The overlap in baseline length between standard and relocation configurations is detailed in this graphic. A criteria of at least 50% of baseline length overlap will be used to decide if OBs can be executed on an another onfiguration than the standard one. Based on this criteria, this table gives the correspondence between actual AT quadruplets and classification in terms of "small", "medium", "large" and ''astrometric" configurations.

As it is the case since P101, some single-feed observing blocks of service mode runs requesting the large configuration might still be executed on the astrometric configuration instead since it offers similar baseline lengths and sky coverage.

Configurations offered using the Auxiliary Telescopes

The users are requested to provide their chosen AT quadruplet in their proposal at phase 1. The quadruplet cannot be changed after proposal submission.

Configurations offered using the Unit Telescopes

PIONIER, MATISSE and GRAVITY are offered on the quadruplet UT1-UT2-UT3-UT4.

Configurations from previous periods

For reference, the configurations used in the previous periods can be found on this page.

Observations preparations

For details on the offered modes please refer to the current Call for Proposals and the VLTI manual. In all cases, please verify your observations with ESO tool VisCalc, or alternatively, with the third party preparation software Aspro2, developped with inputs from ESO.