This page is focussed on the operational contraints for FINITO as an external fringe tracker for AMBER and is not aimed at explaining the working of FINITO. The user should be aware that FINITO will take 70% of the H band flux and thus if the user is interested in the H-band in LR-HK the DIT should be increased accordingly. Note that the DIT is only specified in the Phase II stage if FINITO is requested.

Operational Contraints

For FINITO to yield a sufficient fringe locking ratio the object (the same as the one being observed with AMBER) has to fullfill the following criteria:

• Source H magnitude brighter than 3.
• The source visibility in the H band >15%. Assuming the same size in K and H band of the object this would mean that the K visibility has to be larger than 20%. This is not necessarily true for all type of objects. The user should be aware that this is the size of the object in the continuum and not in any emission or absorption lines.
• The Airmass of the observation has to be smaller than 1.5

Weather Constraints

The FINITO weather constraints are stricter than the general AMBER constraints. The nominal performance is reached at:

• Seeing <1.0"
• Coherence time >3ms
• Sky transparency = Clear

FINITO will not perform if:

• Seeing >1.2"
• Coherence time <2.5ms
• Sky transparency = Thick

A user with an object close to the Operational Constraints or close to the limiting magnitude for AMBER (K=3) should request weather conditions equal or better than the nominal weather conditions.