期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 458, 期 2, 页码 1548-1558出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stw369
关键词
dynamo; stars: activity; stars: late-type; stars: magnetic field; stars: mass loss; X-rays: stars
资金
- Simons Fellowship
- IBM-Einstein Fellowship Fund
- NASA through Hubble Fellowship - Space Telescope Science Institute [HST-HF2-51346.001-A]
- NASA [NAS 5-26555]
- [NSF-AST-1109285]
- [HST-AR-13916.002]
Late-type main-sequence stars exhibit an X-ray to bolometric flux ratio that depends on , the ratio of rotation period to convective turnover time, as with 2 a parts per thousand currency sign zeta a parts per thousand currency sign 3 for, but saturates with |zeta| < 0.2 for . Saturated stars are younger than unsaturated stars and show a broader spread of rotation rates and X-ray activity. The unsaturated stars have magnetic fields and rotation speeds that scale roughly with the square root of their age, though possibly flattening for stars older than the Sun. The connection between faster rotators, stronger fields, and higher activity has been established observationally, but a theory for the unified time-evolution of X-ray luminosity, rotation, magnetic field and mass loss that captures the above trends has been lacking. Here we derive a minimalist holistic framework for the time evolution of these quantities built from combining a Parker wind with new ingredients: (1) explicit sourcing of both the thermal energy launching the wind and the X-ray luminosity via dynamo produced magnetic fields; (2) explicit coupling of X-ray activity and mass-loss saturation to dynamo saturation (via magnetic helicity build-up and convection eddy shredding); (3) use of coronal equilibrium to determine how magnetic energy is divided into wind and X-ray contributions. For solar-type stars younger than the Sun, we infer conduction to be a subdominant power loss compared to X-rays and wind. For older stars, conduction is more important, possibly quenching the wind and reducing angular momentum loss. We focus on the time evolution for stars younger than the Sun, highlighting what is possible for further generalizations. Overall, the approach shows promise towards a unified explanation of all of the aforementioned observational trends.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据