Deep Convection and the Solar Chromosphere

Lämmer

et al. 2016

ApJ

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 t t --log log log 2 log 1 2 1has 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.

Section: Analysis Of Harmonic Amplitudesmentioning

confidence: 99%

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

Lämmer

et al. 2016

ApJ

“…For the Sun, the vertical transport of the magnetic field has been used to probe the convective zone (CZ; Arkhypov et al 2012). Active regions on the solar surface are generally thought to originate from a toroidal magnetic field generated by dynamo mechanisms operating at the base of the solar CZ (Tobias 2002).…”

Section: Introductionmentioning

confidence: 99%

Signs of deep mixing in starspot variability

Güdel

et al. 2015

A&A

Self Cite

The current knowledge on plasma mixing in stellar interiors is based on theoretical modeling, which calibrates the empirical relations between the mixing and observable stellar parameters. Hence, a model-independent method of studying the mixing process is a desirable, but yet unfounded approach. Here, using a new spectral-correlation method, verified for the Sun, we show that deep mixing is manifested in stellar photometric light curves. We measure the timescales of the stochastic change in the spectral power of rotational variability of hundreds of main-sequence stars from the Kepler mission archive. The discovered proportionality of these timescales to the turnover time of the standard mixing length theory, their consistency with Kolmogorov's theory of turbulence, and the relation with stellar activity provide a new approach to the probing of stellar interiors. This opens a broad perspective for experimental studies of deep mixing and magnetic dynamos in stars.

“…In the successful MLT this turnover time is attributed to the standard (i.e., laminar) convective cells at the bottom of the convection zone (e.g., Gilliland 1985). The decaying giant (∼45 o ) cells of laminar convection in turbulence were modeled in the solar convection zone (e.g., Brun & Toomre 2002) and indirectly detected in solar activity patterns (Arkhypov et al 2012(Arkhypov et al , 2013 and in the regular drift of supergranules (Hathaway et al 2013). However, the directly observed solar photospheric granulation and even subphotospheric supergranules have much smaller diameters ( 0.4 o ) and shorter lifetimes ( 1.8 day; Rieutord & Rincon 2010) than the scales τ MLT and τ lam1,2 (>10 days) in Fig.…”

Section: Discussionmentioning

confidence: 99%

Timescales of starspot variability in slow rotators

Güdel

et al. 2018

A&A

Self Cite

There is an intriguing proximity between the turnover time τMLT of the standard mixing length theory of the Sun and the timescale τlam of solar activity patterns at the space scale of giant laminar convection assumed in deep layers of the Sun. To verify the reliability of this correspondence, we analyzed the light curves of 637 slowly rotating stars, observed by the Kepler mission, with periods from 16 to 30 days. The proximity τMLT ≈ τlam is confirmed. The performed study also confirms the manifestation of large scale turbulence in the dynamics of surface activity such as that in the Sun. These results open a new way to measure the key astrophysical parameter τMLT and to study deep convection that has been undetected with asteroseismology.