2009/01/12 by A. Reiners, Ansgar Reiners, Gibor Basri +1
Physics and Astronomy · #Astronomy and Astrophysical Research #Scientific Research and Discoveries #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.1051/0004-6361:200811450
5 pages, accepted by A&A
arxiv created 2009/01/12 · openalex publication_date 2009/01/14 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
We compare the amount of magnetic flux measured in Stokes <i>V<i/> and Stokes <i>I<i/> in a sample of early- and mid-M stars around the boundary to full convection (~M 3.5). Early-M stars possess a radiative core, mid-M stars are fully convective. While Stokes <i>V<i/> is sensitive to the net polarity of magnetic flux arising mainly from large-scale configurations, Stokes <i>I<i/> measurements can see the total mean flux. We find that in early-M dwarfs, only ~6% of the total magnetic flux is detected in Stokes <i>V<i/>. This ratio is more than twice as large, ~14%, in fully convective mid-M dwarfs. The bulk of the magnetic flux on M-dwarfs is not seen in Stokes <i>V<i/>. This is presumably because magnetic flux is mainly stored in small scale components. There is also more to learn about the effect of the weak-field approximation on the accuracy of strong field detections. In our limited sample, we see evidence for a change in magnetic topology at the boundary to full convection. Fully convective stars store a 2–3 times higher fraction of their flux in fields visible to Stokes <i>V<i/>. We estimate the total magnetic energy detected in Stokes <i>I<i/> and compare it to results from Stokes <i>V<i/>. We find that in early-M dwarfs only ~0.5% of the total magnetic energy is detected in Stokes <i>V<i/> while this fraction is ~2.5% in mid-M dwarfs.