MUSE Narrow Field Mode Science Verification



General Information

An integral part of the commissioning of a new instrument at the VLT is the Science Verification (SV) phase. SV programmes include a set of typical scientific observations that should verify and demonstrate to the community the capabilities of the new instrument in the operational framework of the VLT Observatory. In accordance with its SV Policy and Procedures  ESO encourages the community to submit also highly challenging or risky science observations that will push MUSE/AOF and the VLT to its limits in order to better understand the performance parameter space and its envelope. Such observations should focus on the instruments core modes in order to benefit a wide community.

MUSE, the Multi-Unit Spectroscopic Explorer, is an Integral Field Spectrograph located at the Nasmyth B focus of Yepun, the VLT UT4 telescope. It has a modular structure composed of 24 identical IFU modules that together sample, in Narrow Field Mode (NFM), a near-contiguous 7.5" x 7.5" field of view. Spectrally the instrument samples almost the full optical domain with a mean resolution of 3000. With the GALACSI Adaptive Optics system in combination with the VLT Adaptive Optics Facility, MUSE will offer an AO-corrected 7.5" x 7.5" field of view with 25 mas sampling.

The new adaptive-optics assisted MUSE mode is offered to the community for SV for 5 nights in August 2018. All astronomers are invited to participate in this opportunity to obtain unique science with the MUSE AO-supported NFM and thus to demonstrate its scientific capabilities. A call for proposals has been issued and the community was invited to submit proposals for the MUSE NFM science verification using the simplified proposal template. The deadline for this call for proposals is 30 May 2018, 18:00 CEST.

Proposals will be reviewed by an internal panel and allocated time on the basis of scientific merit and feasibility, as well as in the demonstrated ability of the Principle Investigators to deliver results on a timely basis.

The observations will be conducted during the nights of 7-12 August 2018 in Service Mode by a dedicated team of ESO astronomers. The MUSE NFM SV team will be able to assist the successful PI’s in the preparation and optimisation of the OB’s on a best effort basis only.

The latest version of the MUSE data reduction pipeline will be available for reduction of the SV data. Proposers are reminded that all SV data are made public worldwide immediately after passing the usual quality control checks.


Short description of the MUSE NFM

GALACSI is an AO system developed to increase the performance of MUSE. When the NFM is selected, GALACSI uses a 4 laser guide star system (LGS), the deformable secondary mirror on UT4, and an InfraRed Low Order Sensor (IRLOS) to provide a near diffraction limited resolution at visible wavelengths (i.e. SR>5% at 650 nm for 0.6” seeing). IRLOS senses and corrects the tip-tilt and focus by using a Natural Guide Star (NGS) of magnitude in the range 5 < H < 14, which must be located within a radius of 3.35" from the center of the MUSE FoV (see Fig. 1). Extended objects can be also use as NGS providing their magnitude within  an aperture up to ~3" is in the range speified above. With the 4 LGS close to the optical axis (i.e. ~10" off-axis, see Fig.1), the whole turbulence volume around the telescope axis is probed, allowing to measure wavefront errors and to compute deformable secondary mirror commands through Laser Tomography AO algorithms.

Further information on the NFM can be found here.

An updated version of the MUSE ETC is now available here.

NOTE on OPERATION: If the NGS is not on-axis (i.e. NGS is not the target) then it is not possiple to apply the usual rotation between consecutive exposures, therefore in order to optimise the cosmics rejection and obtaining a uniform combined dataset in terms of noise properties exposures dithering is mandatory. In NFM the dithering pattern is performed in closed loop to minimise the overheads, therefore it is not only limited by the size of the NGS patrol field (i.e. the offsets pattern must be confined within a circle of 3.35" radius centred on the target). The offset between consecutive exposures cannot be larger than 8 pixels. Finally, mosaicking within the same OB is not possible in NFM.


Figure 1: MUSE and GALACSI layout in NFM. Solid black square marks the MUSE scientific FoV (7.5"x7.5"), and the dashed magenta circle refers to the NGS patrol field (circle of 3.35" radius centred on the MUSE FoV center). The 4 big yellow stars represent the 4 LGS which are kept outside the MUSE FoV ( ~10" off-axis).
Table 1: Summary of the NFM characteristics and performances