Stellar differential rotation and coronal time-scales
Abstract
We investigate the time-scales of evolution of stellar coronae in response to surface differential rotation and diffusion. To quantify this, we study both the formation time and lifetime of a magnetic flux rope in a decaying bipolar active region. We apply a magnetic flux transport model to prescribe the evolution of the stellar photospheric field, and use this to drive the evolution of the coronal magnetic field via a magnetofrictional technique. Increasing the differential rotation (i.e. decreasing the equator-pole lap time) decreases the flux rope formation time. We find that the formation time is dependent upon the lap time and the surface diffusion time-scale through the relation τ_Form ∝ √{τ_Lapτ_Diff}. In contrast, the lifetimes of flux ropes are proportional to the lap time (τLife∝τLap). With this, flux ropes on stars with a differential rotation of more than eight times the solar value have a lifetime of less than 2 d. As a consequence, we propose that features such as solar-like quiescent prominences may not be easily observable on such stars, as the lifetimes of the flux ropes which host the cool plasma are very short. We conclude that such high differential rotation stars may have very dynamical coronae.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2014
- DOI:
- 10.1093/mnras/stu1415
- arXiv:
- arXiv:1407.3388
- Bibcode:
- 2014MNRAS.443.3251G
- Keywords:
-
- stars: activity;
- stars: coronae;
- stars: magnetic field;
- stars: rotation;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- MNRAS (October 1, 2014) 443 (4): 3251-3259