La Silla - Science Operation Department

TIMMI2 overview

TIMMI2, Thermal Infrared Multi-Mode Instrument 2

TIMMI2 is a multi mode (imaging, polarimetry, and long slit spectroscopy) thermal-infrared (4-20 um) instrument working at the ESO/3.6m Cassegrain, f/35 focus. When the instrument is installed, the f/8 top unit is replaced by the f/35 chopping unit, housing a gold-coated mirror. On the footprint of the Cassegrain hole of this secondary mirror, another tilted mirror is intalled, to reflect away the thermal radiation from the hole itself. Lenses offering different magnifications are available in the different bands: 0.3”/px in the L and M bands; 0.2”/px and 0.3”/px in the N band; and 0.2”/px in the Q band. In the N band, the background often saturates the array when the 0.3”/px lens is used, so it's usually best to use the 0.2”/px. However in periods of low background, the 0.3”/px lens gives a chance to somewhat increase the small field of view.

The array is a Si:As chip manufactured by Raytheon, with format 320 x 240 pixels (the px size is 50 um), distributed in 16 channels of 20 columns each. So the field sizes are 64”x48” or 96”x72” for the small and large field lenses, respectively. It's sensitive from 2um to 28um, with a mean QE=31.6%, a read noise of 922e-, a full well capacity of 1.13x10⁷/2.04x10⁷e- (high/low gain), and a dark current < 100e-/sec at T=6K.

Below we summarise in two tables the operational modes and performance of TIMMI2. Those tables are intended as quick feasibility references only, proposers should refer to the detailed information (e.g. User's Manual, Exposure Time Calculator).

For Period 76 all TIMMI2 instrument modes, except polarimetry, will be offered in both Visitor Mode and in Service Mode. An intervention to improve the polarimeter stability is being planned. Depending on the outcome, the polarimeter could be offered again. Keep an eye on the TIMMI2 pages for news.