Deep Mixing in Stellar Variability: Improved Method, Statistics, and Applications

Author(s)
O. V. Arkhypov, Maxim L. Khodachenko, Helmut Lammer, Manuel Güdel, Theresa Rank-Lüftinger, Colin Johnstone
Abstract

The preliminary results on deep-mixing manifestations in stellar variability are tested using our improved method and extended data set. We measure the timescales τ

m of the stochastic change in the spectral power of rotational harmonics with numbers m ≤ 3 in the light curves of 1361 main-sequence stars from the Kepler mission archive. We find that the gradient has a histogram maximum at -2/3, demonstrating agreement with Kolmogorov's theory of turbulence and therefore confirming the manifestation of deep mixing. The squared amplitudes of the first and second rotational harmonics, corrected for integral photometry distortion, also show a quasi-Kolmogorov character with spectral index ≈-5/3. Moreover, the reduction of τ

1 and τ

2 to the timescales τ

lam1 and τ

lam2 of laminar convection in the deep stellar layers reveals the proximity of both τ

lam1 and τ

lam2 to the turnover time τ

MLT of standard mixing length theory. Considering this result, we use the obtained stellar variability timescales instead of τ

MLT in our analysis of the relation between stellar activity and the Rossby number P/τ

MLT. Comparison of our diagrams with previous results and theoretical expectations shows that best-fit correspondence is achieved for τ

lam1, which can therefore be used as an analog of τ

MLT. This means that the laminar component (giant cells) of stellar turbulent convection indeed plays an important role in the physics of stars. Additionally, we estimate the diffusivity of magnetic elements in stellar photospheres.

Organisation(s)
Department of Astrophysics
External organisation(s)
Österreichische Akademie der Wissenschaften (ÖAW), University of Texas, Austin
Journal
The Astrophysical Journal
Volume
826
No. of pages
17
ISSN
0004-637X
DOI
https://doi.org/10.3847/0004-637X/826/1/35
Publication date
07-2016
Peer reviewed
Yes
Austrian Fields of Science 2012
103003 Astronomy, 103004 Astrophysics
Keywords
ASJC Scopus subject areas
Astronomy and Astrophysics, Space and Planetary Science
Portal url
https://ucrisportal.univie.ac.at/en/publications/82e660cd-5285-43bc-bf2c-cdadfa4d0f99