Other
Scientific paper
Sep 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011head...12.1006w&link_type=abstract
American Astronomical Society, HEAD meeting #12, #10.06
Other
Scientific paper
Stellar activity and angular momentum operate in a feedback loop via the magnetic dynamo and coronally-driven stellar winds. Despite far-reaching implications of this from Solar activity and stellar chronology to the formation of close binaries and Supernova 1a progenitors we are far from a complete understanding of how these properties evolve over a stellar lifetime as well as the form of the underlying dynamo.
We present the results of multiple studies designed to probe the stellar activity-rotation relationship. Using both an unbiased sample of stars with X-ray luminosities and rotation periods, and the results of a new Galactic X-ray population model we find a steep decay of X-ray activity with Rossby number that is inconsistent with a distributed dynamo model. This argues for an additional term in the dynamo number equation. Based on a scaling analysis for an interface dynamo we find this additional term implies that the fractional differential rotaiton of solar-type stars scales with the angular rotation rate to the power of two-thirds.
Using our sample of high activity stars we conclusively observe supersaturation in the fastest rotators and show that it correlates with both the corotation radius and excess polar updraft. The latter theory (Stepien 2001) offers a stronger correlation, and is supported by other observations.
Finally, the color-dependent form of the saturation threshold are used to show that coronal stripping is unlikely to be responsible for this effect. Instead we suggest that a different dynamo configuration is actually at work in stars with saturated coronal emission, resulting in a different parameterization of the X-ray emission level (causing apparent saturation under certain parameters). This assertion is backed up by the correlation between the empirically-determined saturation threshold and the time at which stars transition from the convective to the interface sequences in models of rotation spin-down.
Drake Jeremy J.
Mamajek Eric E.
Wright Nicholas James
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