CORDIS - EU research results

Magnetic fields and the outflows during the formation and evolution of stars

Mid-Term Report Summary - OUTFLOWMAGN (Magnetic fields and the outflows during the formation and evolution of stars)

The interstellar medium (ISM) is enriched with the elements needed to form new stars and planets by means of stellar outflows and supernova (SN) explosions. Fusion processes in stars that are only up to a few times more massive than the Sun form many of the elements, up to iron. Most of these elements are formed and expelled in a dense wind when the star is approaching the end of its life, during the giant phases such as the asymptotic giant branch (AGB). The even heavier elements are formed in massive stars that explode as supernovae. In addition to molecules and atoms, AGB stars and supernovae are the main sources of interstellar dust.

However, both the formation of massive stars as well as the origin of the dense stellar winds are still not fully understood. Until such proper understanding is formed, studies of the formation and evolution of galaxies and stars will remain susceptible to systematic uncertainties. A number of questions concerns the role of the magnetic field, which is known to be ubiquitous throughout the universe, occurring from around planets out to the intergalactic medium. With instrumental advances, we are now able to push well beyond the current state of the art in our studies of circumstellar and proto-stellar magnetic fields, and stellar outflows in general. Specifically the new high spatial resolution radio- and submm instruments (e.g. ALMA, LOFAR) are now opening important new areas of study.

In this ERC consolidator group, the main question that we address is:
Does the magnetic field control massive star formation and the interstellar enrichment through evolved stellar mass loss?

This question has a number of sub-topics that concern e.g. the study of outflow mechanisms, exoplanet interaction and stellar activity as sources of magnetic fields, and the investigation of new probes of the inner regions around stars, where the outflows are launched. Already now, we have been able to make significant steps in our knowledge, even if several projects are still in their infancy.

Some of the early results of the project include:
- Upper limits of the low-frequency (LOFAR) radio emission produced by the magnetic late-type stellar wind and its several Jupiter mass exoplanet. Although no detection was made, the observations show what we need to aim for with observations with the next generation of radio telescopes, the Square Kilometer Array (SKA). The project did produce a detailed study of the stellar wind at progressively shorter wavelengths, which provides important upper limits on the mass-loss rates and wind driving.

- The detection of bright hotspots on an evolved star using the highest possible angular resolution provided by ALMA. The hotspot is reminiscent of the activity seen on the Sun even if the star is several times larger.

- We have expanded the number of massive star forming regions for which magnetic field information is present. Our analysis shows that the magnetic field appears aligned with large scale stellar outflows, proving the importance of magnetic fields at these stages of evolution.

- We have made the first scattered light polarisation images resolving an AGB star. These observations identify the region where the dust is formed and the outflow is driven. The initial analysis shows that the observations are not easy to reconcile with current models for this particular star. Further observations are being performed.

In order to properly analyse the data that will be needed to answer our main questions, we have also continued the development of better tools to derive magnetic field strengths and morphologies. This includes the quantum chemical description of Zeeman splitting of the methanol molecule as well as improvements to three-dimensional radiative transfer codes to model the polarisation of molecular lines that will be observed with ALMA.