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Surface magnetism of cool stars

A Cool Stars 19 splinter session

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Image credit: ESO/Oleg Kochukhov

Image credit: AIP

Session organizers

Invited speakers

Scientific Motivation

Magnetism is an important, yet incompletely characterized and poorly understood, ingredient of stellar physics. Magnetic fields are playing a key role in stellar evolution, including accretion processes in young stars, angular momentum loss, internal mixing. The fields of cool stars govern dynamic, energetic phenomena on stellar surfaces and significantly influence the stellar environments, including planetary systems. Understanding, e.g., the cyclic behavior of cool star magnetic fields is critical for assessing possible impact of the solar variability on our terrestrial climate.

An analysis of the Zeeman effect in spectral lines is the only source of direct information about the strengths and topologies of stellar magnetic fields. During recent years significant progress has been made by magnetic broadening and Zeeman-Doppler imaging (ZDI) studies of cool stars. On the one hand, more physically refined and numerically sophisticated analysis techniques were developed. The number of objects studied with these methods has increased significantly. This allowed establishing the presence of magnetic fields in essentially all classes of cool stars and revealing unexpected trends with stellar parameters. Moreover, long-term monitoring of a handful of sun-like stars yielded first direct observations of magnetic cycles. At the same time, some puzzling discrepancies between results of the application of different diagnostic methods have been identified, suggesting that certain aspects of modern observations are not fully understood or even misinterpreted.

This splinter session aims to provide a comprehensive overview of recent results of the direct studies of magnetic fields at the surfaces of different classes of cool stars. Special emphasis will be given to the discussion of the reliability and consistency of different magnetic indicators and to the comparison of results obtained by different research groups.

Topics covered by the session may include:


14:00 Welcome
14:05 Klaus Strassmeier Methods of direct studies of stellar surface magnetic fields (invited)
14:30 Lisa Rosén Challenges of cool star ZDI: self-consistency and four Stokes parameters
14:45 Sandra Jeffers Magnetic cycles of solar-type stars
15:00 Heidi Korhonen Imaging stellar surfaces with near-infrared interferometry: comparison to Doppler imaging results
15:15 Colin Folsom Magnetic fields of young cool stars  (invited)
15:40 Coffee break
15:55 Belinda Nicholson Magnetic fields of weak-line T Tauri stars
16:10 Julien Morin Magnetic fields of low-mass stars (invited)
16:35 Denis Shulyak Beyond the saturation: detecting the strongest magnetic fields in M dwarf stars
16:50 Rim Fares Tomographic imaging: the Sun as a test case
17:05 Arturo López Ariste Solar and stellar spectropolarimetry: A comparison (invited)


We are envisioning a single, jointly co-authored review paper including all presenters of the splinter in a refereed issue of Astronomische Nachrichten / Astronomical Notes. Examples of such summary reviews were the stellar magnetism and differential-rotation splinter at CS 17 in AN 334, 48 and AN 334, 89. Every presenter will be asked to contribute a chapter to the paper of length appropriate for the topic.


Questions about this splinter session can be directed to