VLT Laser Guide Star Facility Policies

(Prepared/Revised: O.Hainaut 2007-03-31 - Approved: A.Kaufer 2007-04-01 - Released: C.Cesarsky 2007-04-01)

Purpose of this Document

In the following we describe the Paranal Science Operations policies for the operation of the Laser Guide Star Facility (LGSF). These policies are in place since the beginning of the ESO Observing Period 79.

The complete LGSF Operations Plan is described in VLT-PLA-ESO-11860-2290.

Beam Collision

The operation of the LGSF creates two sources of potential interference with the observations of neighbouring telescopes on Paranal (UT1,2,3, ATs, ASM, and in the future VISTA and VST): first the laser guide star itself, and the second the Rayleigh and Mie scattered laser cone. In case any of the two sources contaminates and/or interferes with the observation of another telescope, we refer to a beam collision

To avoid beam collisions, the minimum separation between the Rayleigh cone or the laser star and a non-laser observation is 3 arcmin, equivalent to a flux decrease of 3 orders of magnitude. For this avoidance zone it has to be considered that the laser guide star, and in particular, the laser cone appear at different positions on the sky when seen from different telescopes.

Science Operations Policies for LGSF Observations

Safety policy: the LGSF shall be operated only when the Aircraft Avoidance System is operational and online. LGSF operations shall immediately suspended should this system be unavailable.

As a general policy, also followed by other astronomical observatories,
observations performed with the LGSF have lower priority than observations on any other telescope.
This general policy is implemented on Paranal as follows:

The general policy is amended as follows:

Observational Mode

Meteorological and atmospheric conditions have a much greater impact on AO-LGS observations than on classical observations. As these conditions can change rapidly during the night, even short term planning is difficult.

In order to achieve the necessary flexibility with minimum negative impact on the scientific output of UT4, and to gain the necessary on-site experience, AO-LGS observations are currently restricted to Service Mode only (with the exception of LGS GTO observations which are executed in Visitor Mode only).