Ground-based astronomical observations in the thermal IR wavelength regime (3-30 micron) provide a powerful tool to discover and characterise the most obscured sources in the Universe. Thermal IR instruments serve a broad range of astronomical disciplines from protoplanetary disks, the building blocks of planets, to active galactic nuclei, the surroundings of accreting supermassive black holes. The thermal IR is also the wavelength of choice to characterise exoplanet atmospheric composition and motions, and most sensitive for probing Earth-like exoplanet atmospheres.
While space-based instruments offer the ultimate sensitivity, observations from the ground are unrivalled in terms of spatial and spectral resolution. Thanks to regular upgrades, they are also the preferred testbed for new technologies or exciting experiments such as recently demonstrated with NEAR at the VLT.
These critical science areas push instruments to their limits, demanding sensitivity, stability and contrast which ultimately rely on complete instrument characterisation and calibration. This topic is therefore extremely relevant for all major current astronomical observatories which host thermal-IR cameras, such as VLT/VISIR, VLTI/MATISSE and GranTeCan/CanariCam. Calibration in the thermal IR will be even more important to reach the ambitious science goals of the next generation facilities: characterising earth-like exo-planets is one of the prime science cases of METIS, a first-light instrument for the European Extremely Large Telescope (2025).
This is no small feat since, in the thermal IR, sources of astrophysical relevance have to stand out against the glaring background from the atmosphere and warm telescope optics at a rate of typically 1 : 10^6. With the more complex, five-mirror design of the ELT, systematic residuals in the subtraction of the thermal background will increase. At the same time, however, more stable detectors are becoming available in the thermal IR and computing power is no longer a limitation for exploring new observing and analysis techniques.
In this workshop we aim to bring together the experts in the field to review the science highlights from ESO's thermal IR instruments TIMMI, TIMMI2, VISIR, MIDI and MATISSE as well as those at other observatories, such as COMICS, Michelle and T-ReCS. We will review some future facilities, and we will compare techniques and approaches for observations and calibrations, with the aim to reach the theoretical limit, the background-limited performance.