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Imaging- and spectropolarimetry in the thermal infrared (~ 5-30 μm) can inform us about two important open
questions in modern astrophysics - namely the role of magnetism in the formation of stars, and the life-cycle
of cosmic dust. These are key questions outlined in the document "A Science Vision for European Astronomy"
by de Zeeuw & Molster (2007). Thermal IR polarimetry is the only technique that can peer into the heart of
star forming cores, where an infant star heats its immediate surroundings to temperatures of several hundred
Kelvin. The polarization itself is induced by a preferential alignment of the spin axis of cosmic dust grains, a
process ultimately controlled by the ambient magnetic field. The spectrum is sensitively dependent on the grain
optical properties, structure and shape, thus providing information not otherwise obtainable by conventional
spectroscopy. The MIRI instrument on the JWST will not have a polarimetry mode, thus leaving open the
possibility of an ELT mid-IR instrument being able to make substantial progress on these fundamental issues.
Before describing the advantages of a mid-IR spectropolarimeter on an ELT, we first present some preliminary
results from our polarization observations with the TIMMI2 mid-IR instrument between 2004 and 2006. The
experience gained with TIMMI2 - in terms of technical issues and observing strategy - will inform the design of
any future instrument. Following this we will describe the science that could be done with an ELT instrument,
and some of the basic design parameters. For instance, with a resolution of ~ 70 milli-arcseconds (FWHM at
10 μm) it will become possible to resolve the magnetic field configuration in the circumstellar disks and bipolar
outflows of young stars at a spatial scale of less than 10 AU in the nearest star formation regions. This will
strongly constrain hydromagnetic models - the favoured means of extracting angular momentum and allowing
accretion to proceed - for bipolar jets emanating from a range of compact astrophysical objects. Further, with
a resolving power of order 200, and sensitivity of 100σ in 1 hour integration on a 0.5 mJy point source, the
evolution of cosmic dust - and the governing physical and chemical processes - from its formation in old stellar
outflows to its deposition in planet-forming disks, will become amenable to detailed polarization studies.
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