Overview

Important

August 27, 2014: As re-commissioning after the VISIR upgrade is still on-going, for ESO period 95 VISIR will be offered for a limited set of observing modes (regular imaging with the 0.045" pixel scale,  low-resolution spectroscopy, and high-resolution long-slit and cross-dispersed spectroscopy) only. Chop throws will be limited to 10". As at the time of writing the final sensitivities are still being established, for the purpose of proposal preparation, please assume he pre-upgrade sensitivities.

Imaging and long-slit spectroscopy with VISIR can be achieved at several spatial and spectral resolution. The imager and spectrograph are two sub-instruments. They have independent light paths, optics and detectors. The spectrometer has two arms, one with low order gratings for the low and medium spectral resolution, the other with large echelle gratings providing high spectral resolution. The cryogenic optical bench is enclosed in a vacuum vessel. The vessel is a cylinder, 1.2m long and 1.5m in diameter. Standard Gifford-McMahon closed-cycle coolers are used to maintain the required temperature: 33K for most of the structure and optics and < 15K for the parts near the detector. The detectors are cooled down to ~7K. The imager can be used either in standard readout mode or in burst readout mode.

Imaging

spectral range [µm]  pixel field of view [arcsec] total field of view [arcsec^2] filter 

8 -13, 17 - 24

8 -13, 17 - 24


0.045

0.076


40.0 x 40.0

62.0 x 62.0


broad and narrow band filters

pfov is selectable for both wavelength regions

Spectroscopy

grating offered wavelengths [µm] resolving power
low resolution (LR) 8-13 µm R ~ 350 at 10 µm
medium resolution (MR) 7.5 to 9.3 µm, 10.2 to 13.0 µm, 17.1 to 19.0 µm, 20.12 µm R ~ 3200 at 10 µm
high resolution - long slit (HR) 8.02, 12.81 and 17.03 µm R ~ 25000 at 10 µm
HR - cross dispersed (HRX) 8.970 - 9.140 µm, 9.360 - 9.690 µm, 10.480 - 10.540 µm, 11.540 - 11.570 µm, 11.762 µm, 12.210 - 12.760 µm, 12.814 - 13.364 µm, 16.390 µm, 16.925 µm, 17.790 - 17.980 µm, 18.246 µm, 18.680 - 18.960 µm, 21.295 µm R ~ 25000 at 10 µm

The slits offered have selectable widths of 0.4", 0.75" and 1", and a length of 32.3".
In high-resolution, cross-dispersed mode, the slit length is 4.1".