Kraft break

In astronomy, the Kraft break refers to the abrupt decrease in stars' average rotation rates at surface temperatures of about 6200 kelvin. The so-called break was first noted by the astronomer Robert Kraft.[1] The break is understood to separate stars with deep convective envelopes and efficient magnetic dynamos from those without. The dynamos are thought to maintain magnetic fields that transfer angular momentum to the stellar wind, thus slowing down the star's surface through magnetic braking. In hot stars the process is less efficient (because the convective envelopes are shallow) so the stars continue to rotate quickly.[2]

References

Kraft, R. P. (1967), "Studies of Stellar Rotation. V. The Dependence of Rotation on Age among Solar-Type Stars", Astrophysical Journal, 150: 551, Bibcode:1967ApJ...150..551K, doi:10.1086/149359
Maeder, A. (2009), Physics, Formation and Evolution of Rotating Stars (PDF), Astronomy and Astrophysics Library, Bibcode:2009pfer.book.....M, doi:10.1007/978-3-540-76949-1, ISBN 978-3-540-76948-4

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[1] Kraft, R. P. (1967), "Studies of Stellar Rotation. V. The Dependence of Rotation on Age among Solar-Type Stars", Astrophysical Journal, 150: 551, Bibcode:1967ApJ...150..551K, doi:10.1086/149359

[2] Maeder, A. (2009), Physics, Formation and Evolution of Rotating Stars (PDF), Astronomy and Astrophysics Library, Bibcode:2009pfer.book.....M, doi:10.1007/978-3-540-76949-1, ISBN 978-3-540-76948-4