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Illuminating the role of magnetic fields around dying stars

Final Report Summary - MAGNETIC AGB (Illuminating the role of magnetic fields around dying stars)

The study of the processes governing the end of the life of stars such as our Sun is of fundamental importance. During the final stages of their lives, stars undergo extreme mass-loss in which they expel large amounts of dust, atoms and molecules into the interstellar environment. This material is one of the main sources of the heavy elements essential for further formation of stars, planets and even life. There are now even hints that formation of large dust particles, maybe resulting in planets, is taking place around these dying stars. Although significant advances have been made in recent years, our current understanding of the mass-loss process is however still very incomplete. There are indications of a missing component necessary to drive and shape mass-loss, and magnetism is a possible candidate. These magnetic fields could also explain how non-spherically symmetric planetary nebulae (PNe) are formed from spherical stars.
However, magnetic fields are one of the least studied of the potential mechanisms involved in mass-loss, and, despite being ubiquitous, are often ignored. In this Career Integration Grant project, the effects of magnetic fields on the circumstellar envelope are studied in detail by preparing models that can be compared with observations. With the advent of several new and improved instruments, such as the Atacama Large (sub-)Millimeter Array (ALMA), the observations of magnetic fields (through polarization) will enter a new era. Because sensitive high angular resolution observations will now become commonplace, it will also be possible to observe the results of possible magnetic shaping (including binary effects) directly.
In order to investigate the effect of such shaping on observed molecular line spectra, we have, during this project created a number of analytical models. Further MHD models are now in preparation. During the project we have also made new observations of potential magnetic effects. These include the study of the massive outflow of the Boomerang Nebula, the coldest object in the Universe, which is difficult to be explained using conventional outflow mechanisms, and the detection of molecular isotope variations in the inner envelope of R Scl that require accretion or magnetic stellar activity. Furthermore, we also report on the detection of one of the youngest progenitors of bipolar PNe and found a new molecular probe of the energetic outflows that arise at the end of stellar life. Finally, the direct detection of synchrotron emission from a late stellar jet has proven that magnetic fields are directly involved in collimating the outflows that shape the stellar ejecta. Further recent results include the detection of stellar activity on the surface of an evolved star and significantly anisotropic mass loss, potentially shaped by magnetic processes, around a supergiant star.

Since the molecular line polarization capabilities of ALMA were delayed until the Cycle starting October 2016, we have not yet obtained ALMA observations. I have however recently been awarded an A-rated project to do the first such observations with ALMA, so results will appear during the next year.