Stellar Evidence That the Solar Dynamo May Be in Transition
Abstract
Precise photometry from the Kepler space telescope allows not only the measurement of rotation in solar-type field stars, but also the determination of reliable masses and ages from asteroseismology. These critical data have recently provided the first opportunity to calibrate rotation-age relations for stars older than the Sun. The evolutionary picture that emerges is surprising: beyond middle-age the efficiency of magnetic braking is dramatically reduced, implying a fundamental change in angular momentum loss beyond a critical Rossby number (Ro ∼ 2). We compile published chromospheric activity measurements for the sample of Kepler asteroseismic targets that were used to establish the new rotation-age relations. We use these data along with a sample of well-characterized solar analogs from the Mount Wilson HK survey to develop a qualitative scenario connecting the evolution of chromospheric activity to a fundamental shift in the character of differential rotation. We conclude that the Sun may be in a transitional evolutionary phase, and that its magnetic cycle might represent a special case of stellar dynamo theory.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2016
- DOI:
- 10.3847/2041-8205/826/1/L2
- arXiv:
- arXiv:1606.01926
- Bibcode:
- 2016ApJ...826L...2M
- Keywords:
-
- stars: activity;
- stars: evolution;
- stars: magnetic field;
- stars: rotation;
- stars: solar-type;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 7 pages, 2 tables, 2 figures. ApJL accepted, Colloquium available at https://youtu.be/_3MdLAt8i-o