Scientific rationale
Astrophysical plasmas and magnetic fields are inextricably coupled to each other. But magnetic fields are elusive; they cannot be fully characterized with standard (spectroscopic) observational techniques. Fortunately, polarisation, the third fundamental property of light, encodes all the quantitative information on the magnetism of the objects we observe. This splinter session will bring together the solar and stellar spectropolarimetric communities to discuss some of the fundamental unsolved questions of solar and stellar magnetism and the future of spectropolarimetric observations. Spectropolarimetry has a long tradition in solar physics; it has allowed us to study in detail magnetism throughout the solar atmosphere. It is a consolidated field, although new techniques are emerging which are challenging our knowledge of the generation of magnetic fields in astrophysical plasmas. The great spatial resolution (and polarimetric accuracy) of the present data (Hinode satellite and IMaX onboard Sunrise balloon) has allowed us to study in close detail the intricacies of turbulent magnetism on the solar surface, the so-called quiet Sun magnetism, or the fine structure of prominences and spicules. But it has also created new questions: How the solar atmosphere is magnetically coupled? How do magnetic fields emerge in the solar photosphere and reach the corona? What is the role of the magnetism in the temperature rise of the outer layers? Which magnetic fields maintain the cold plasma of prominences in the hot corona? All these questions are planned to be presented in the splinter session we propose, with emphasis on how they can also relate to stellar physics. For example, the possible existence of a turbulent magnetism in cool stars and its possible detection, or the magnetic field detection (and study) of magnetic fields in stellar prominences. Stellar spectropolarimetry is a younger discipline which is growing and consolidating rapidly, which is evident from the huge success of high-resolution instruments like ESPaDOnS (CFHT, Mauna Kea) and HARPS (ESO, La Silla). Many questions on stellar magnetism are linked to solar physics, with many of the lessons learnt from the Sun being able to be applied to the stars. Conversly, there are many things we can learn from the stars that can be applied to solar physics: How did the Sun's cyclic dynamo develop? Does the solar magnetic dynamo apply to all types of stars? Can we use the variety of stars to predict if (and when) the Sun will go into another Maunder minimum?
The most important thing we wish to address in this splinter session is the synergy between solar and stellar spectropolarimetry. The main task of the solar-stellar connection is to build the bridge between the detailed knowledge gathered from solar observations and modelling, and the diversity of the stars. The flow of information occurs in both directions: many of the physical principles are known from the Sun, but much about global behaviours and stellar evolution can be learned only from stellar observations. The observation of stars similar to the Sun brings the opportunity to investigate how stellar magnetic activity phenomena vary over a variety of stellar parameters (age, mass, rotation rate, binarity...). These premises are reflected in the recently started COST action named “Spectropolarimetry as a tool to study the solar system and beyond”. New ideas on solar and stellar spectropolarimetry have induced the need for new ground-based facilities: the forthcoming solar ATST and EST ground-based telescopes, and stellar polarimeters that will open new windows of observation such as SPIRou (CFHT, Mauna Kea) and MIRADAS (GTC, Roque de los Muchachos). Moreover, they have promoted the creation of very successful networks like the solar ESMN I and II, and Solaire initiatives, and the stellar MAPP and Bcool projects (which are part of the over aching MagIcS project). This splinter session on solar and stellar spectropolarimetry is timely with the advent of these new ideas and large instrumental projects. In particular, MAPP has been running on the CFHT for some years and is starting to produce excellent results, and the Bcool project and the COST action are starting to develop and are looking to expand their collaboration base. Too often the solar and stellar communities are isolated, when they have much to offer each other. A splinter session on solar and stellar spectropolarimetry at Cool Stars 17 will provide an excellent vehicle to promote collaboration between these two groups.
News :
The final program has been published. Contact us in marian@iac.es or Stephen.Marsden@jcu.edu.au for any detail.