Bando competitivo per il finanziamento di progetti di sviluppo tecnologico Bando TECNO-INAF 2009.

Polarimetry is a powerful diagnostic tool to study astrophysical sources.
Radiation mechanisms that produce similar radiation output can be disentangled by means of their polarization signatures.
Also, polarization provides unique insights into the geometry of unresolved sources, even at cosmological distances, which remains hidden in the integrated light.
Polarization and wavelength are the bits of information attached to every photon that reveal the most about its formation and subsequent history.
In an observational science such as astronomy, this carries even higher weight because polarimetry goes directly to the heart of the problem, i.e. the underlying physical process.

The elementary processes include, among others:

• Scattering (e.g. by dust particles in the interstellar medium).
• Absorption by aligned, intrinsically asymmetric particles (e.g. in molecular clouds).
• Scattering by asymmetrically distributed particles (e.g. in disks).
• Coherent scattering in spectral lines (e.g .in magnetospheres).
• Emission or scattering by asymmetric sources (e.g .supernova explosions).
• Cosmic magnetic and electric fields through Zeeman-, Stark- and Paschen-Pack- effect (e.g. on stellar surfaces).
• Cyclotron or synchrotron radiation, inverse-Compton process and relativistic jets (e.g. AGNs, GRBs, etc.).
• Reflection (e.g. by extra-solar planets).
• Quantum gravity modification of standard dispersion relation (e.g. for cosmological sources).

The increasing importance of polarimetry in many astrophysical contexts is witnessed by the proportional increase in recent years of the number of scientific publications based on optical/NIR polarimetric observations (Schmid 2008, proceedings of "The 2007 ESO Instrument Calibration Workshop").
At the same time, the perspectives for optical/NIR polarimetry as an astronomical tool have been underlined in several Science White Papers prepared for the 2010 US Astronomy and Astrophysics Decadal Survey (Clemens et al., Hines et al., Hoffman et al.).
A fair fraction of these scientific cases are well within the capabilities of a 4m class telescope as the Italian Telescopio Nazionale Galileo (INAF-TNG), which is indeed an internationally recognized competitive facility with still a remarkable instrument set.
In light of this, an optical polarimeter mounted at the INAF-TNG has to be considered as a significative improvement of the telescope instrumentation, complementary to the already existing NIR polarimeter available with NICS.