The VISIR Upgrade Project

Introduction

VISIR, the mid-infrared imager and spectrograph on the Very Large Telescope has now been successfully in operation for more than five years. Since the introduction of VISIR, mid-infrared detector technology has advanced significantly, and ESO, in collaboration with members of the consortium that built VISIR (CEA Saclay, France and ASTRON, the Netherlands) is currently launching a project to upgrade VISIR and its capabilities. A new detector will be the most prominent upgrade to the hardware providing better sensitivity, stability and overcoming the electronic artifacts. Based on feedback from the user community, it was decided that several other measures to optimize hardware, software and operations will also be implemented as part of the VISIR Upgrade Project.

Scope

The main part of the VISIR upgrade project will be the upgrade of its current DRS (former Boeing) 256x256 BIB detector to a Raytheon 1024x1024 pixel Aquarius array. The new detector will offer a larger field-of-view (for imaging), and extended recorded spectral range (for spectroscopy), better cosmetics, and -- especially for spectroscopy -- improved sensitivity. In addition to this main part of the upgrade, several other new features will be implemented:

• During the upgrade project, a prism will be installed in VISIR that will enable the entire N-band (8-12 μm) spectrum to be recorded in a single exposure in low-resolution (R = 200) spectroscopy mode. This new low-resolution prism mode is envisioned to largely replace VISIR's current low-resolution grism spectroscopy mode, which needs four different exposures to cover an equivalent wavelength range. This new observing mode will be offered in both visitor- and service-mode.

• The stability of the images delivered by VISIR will be improved. We are working toward offering diffraction-limited image quality in the N- and Q-bands under median seeing conditions on Paranal with the post-upgrade VISIR.

• New coronographic and sparse aperture masking (SAM) modes will be implemented in the course of the VISIR upgrade project. It is expected that initially these modes would be offered for visitor-mode observations only.

• Precipitable Water Vapour (PWV) is the main source of opacity at mid-infrared wavelengths. Furthermore, the PWV contents of the atmosphere is highly variable. To be able to better match the scientific needs of each programme to the ambient conditions, ESO is installing a PWV monitor on Paranal as part of the VISIR upgrade project. PWV is anticipated to become a user-defined constraint for VISIR service-mode observations starting with ESO period 90.

• The VISIR data-reduction pipeline will be upgraded to support the new detector and the new observing modes. In addition, several existing shortcomings will be remedied.

Schedule

The VISIR Upgrade Project has succesfully passed it Preliminary Design Review (PDR) and Final Design Review (FDR) in September 2010 and July 2011, respectively. VISIR will be unavailable for science observations during the implementation phase of the upgrade project, foreseen for May-August 2012. The post-upgrade VISIR will be offered to the user community for regular science observations at the end of ESO period 89 (from September 2012 onwwards). Further news about the upgrade project will be listed in the News section of this web-page.