Observing constraints requested in Phase 1 proposal are binding

At Phase 1 specific observing conditions (lunar phase also known as Fractional Lunar Illumination or FLI, atmospheric turbulence, and sky transparency) were requested for each observing run. Your run was reviewed and allocated time with these specific conditions in mind.

It is important to notice the difference between atmospheric turbulence constraints at Phase 1 and image quality constraints at Phase 2 (with the exception of AO instruments and VLTI, see the observing conditions definitions for more details). With the help of the Exposure Time Calculators (ETCs) the requested Phase 1 atmospheric turbulence (for seeing limited instruments corresponding to V-band seeing at zenith) can be transformed into the desired image quality at the observed wavelength and airmass for each instrument.

During Phase 2 preparation (and review only), you can relax your constraints, but you cannot specify more stringent constraints. For example,

• if you requested gray moon (g) at Phase 1, then you can relax to bright moon (i.e. FLI>0.7), but cannot specify more stringent dark conditions (i.e. FLI<0.4);
• if you requested Transparency = CLR at Phase 1, you can specify THN or THK at Phase 2, but not PHO.

The only exception to this is the case in which only a small subset of observations need to be obtained under photometric conditions in order to provide an accurate flux calibration - for example, observations of a deep field in which a network of bright flux reference objects can be set up from a shallow exposure. Such exceptions are accepted only if accurate flux calibration is needed for the scientific goals of the programme, and for an execution time not exceeding 20% of the total allocated time.

Also check the Service Mode guidelines on observing constraints.

Target (lists) and Instrument Setup requested in Phase 1 proposal are binding

The submitted proposal has been reviewed and approved for the specific set of targets and instrument setup combination(s). Given the delay between proposing for observations and their execution, with the aim to ensure that the telescope time is used most effectively, it is possible to request moderate and scientifically well justified deviations from the Phase 1 request. However, such requests must not duplicate other approved observations and must be in line with the originally approved science goal. Furthermore, there should be no significant deviation in the location of targets that could affect the scheduling that assumed the original target distribution on sky.

Programme Change Requests are petitions to deviate from observations as proposed at Phase 1 (e.g. new or different targets, new instrument, new/different observing modes, etc.). Formulation and submission of both types of petition is done through the p2 (Paranal) and p2ls (La Silla) user interfaces.