Far Infrared Interferometry for the Observation of Disks

The physical properties of circumstellar disks in terms of spatial scale, density and temperature require to use different observational techniques for different regions of the disks (Akeson 2008). Also, their basic building blocks are gas, dust and ice, which radiate predominantly in the far-infrared wavelength range. 

In general, for thermally emitted radiation from a disk, far-infrared systems can probe the outer ring of a disk (from 10 to a few 100 AU), while mid-infrared telescopes and near-infrared telescopes can observe intermediate radii (about a few AU) and inner rims, respectively. Optical and UV systems can observe regions very close to the stellar surface. 

Spatially, the process of observing a circumstellar disk is not straightforward. To measure disk sizes is difficult because the outer parts are cool and emit weakly. Also, due to their small angular scales in nearby star-forming regions, interferometry is required. For this reason, a far-infrared interferometric system is required. 

Basically, for a full characterisation of stars surrounded by protoplanetary disks in order to understand their evolution, the only solution to meet the spatial and spectral requirements is interferometry from space at the far-infrared wavelength range combined with spectroscopy. 

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