Modeling the Rise of Fibril Magnetic Fields in Fully Convective Stars (Dataset and Additional Visualizations)
Weber, Maria A.
Browning, Matthew K.
The Astrophysical Journal
University of Exeter (dataset)/IOP Publishing (paper)
Creative Commons Attribution (BY) license. Acknowledge source by citing the authors' names, the published ApJ paper, and the ORE handle for the dataset.
This repository contains selected output and visualizations from the work presented in Weber & Browning, 2016 (WB16), now published in The Astrophysical Journal. The work investigates how individual flux tubes in a fully convective 0.3 solar-mass star might rise under the combined influence of buoyancy, convection, and differential rotation. Items B, C, and D are derived from the work published in WB16, but were not included in the article. Images and movies were produced by VAPOR (www.vapor.ucar.edu), a product of the Computational Information Systems Laboratory at the National Center for Atmospheric Research (Boulder, Colorado, USA).
This work was supported by the European Research Council under ERC grant agreement no. 337705 (CHASM) and by a Consolidated Grant from the UK STFC (ST/J001627/1). Some of the calculations for this paper were performed on the DiRAC Complexity machine, jointly funded by STFC and the Large Facilities Capital Fund of BIS, and the University of Exeter supercomputer, a DiRAC Facility jointly funded by STFC, the Large Facilities Capital Fund of BIS, and the University of Exeter.
(A) The file wb2016_tables.tar.gz contains a readme file and nine ASCII text files with columns of selected data output from the thin flux tube simulations presented in WB16. More information regarding the data in these files is contained in a readme_notes.txt file. Figures 11, 12, and 13 in WB16 can be generated directly from these data tables. To access more simulation output, send requests to the authors. (B) Files tube_r50per_b30_th05_TLfC3.jpg and tube_r75per_b30_th05_TLfC3.jpg are images of representative magnetic flux tubes, rendered once some portion has reached the simulation upper boundary at 95% of the total stellar radius. These images correspond to Figures 9a and 9d of WB16, respectively. Each tube has an initial magnetic field strength of 30 kG and latitude of 5 degrees, with the former originating at 50% of the stellar radius and the latter at 75%. The flux tube is colored according to the local magnetic field strength, and is given a 3D extent according to the local cross-sectional radius. As the flux tube evolves, convective motions modulate the shape of the initially toroidal ring, promoting buoyantly rising loops. It is speculated that magnetic structures such as these may give rise to visible starspots on stellar surfaces. (C) Movie of a flux tube rising through the interior of a fully convective star (movie_ASHTFT_r75per_b30_th05_TLfC3.mp4), corresponding to the flux tube in tube_r75per_b30_th05_TLfC3.jpg. Time-varying flows modulate the initially toroidal flux tube. Strong downflows pin portions of the tube to deeper layers, while strong upflows may boost portions toward the surface. The flux tube is colored according to its magnetic field strength, with bluer tones representing stronger magnetic field and yellower tones representing weaker magnetic fields. The convective radial velocity field is also shown, with the strongest downflows in blue and strongest upflows in red. Only a portion of the Northern hemisphere is depicted, from the equator to half of the stellar radius in the vertical direction. Each frame represents about 1.3 days of evolution, with the video elapsing about 110 days. The video ends once the fastest rising portion of the flux tube reaches 95% of the total stellar radius, where the simulation terminates. The orientation has been rotated about 90 degrees from that in tube_r75per_b30_th05_TLfC3.jpg such that the fastest rising loop appears in the center of the visualization domain near the equator at the end of the movie. (D) Giant cell convective flows (movie_ASHvr_130days.mp4) from a 3D simulation of fluid motions representative of a fully convective 0.3 solar-mass, main sequence star computed through the Anelastic Spherical Harmonic (ASH) code. The radial velocity field is shown, with the blue tones representing strong downflows and red tones representing strong upflows. Each frame is separated by about 1.3 days of evolution, with only the Northern hemisphere shown. These flows advect flux tubes in the simulations of WB2016, promoting buoyantly rising structures that may be progenitors of starspots. The duration of the video is about 130 days.
The Astrophysical Journal, 2016, Vol. 827, No. 2