| Issue |
A&A
Volume 681, January 2024
|
|
|---|---|---|
| Article Number | A32 | |
| Number of page(s) | 11 | |
| Section | Stellar atmospheres | |
| DOI | https://doi.org/10.1051/0004-6361/202346460 | |
| Published online | 05 January 2024 | |
Small-scale dynamo in cool stars
III. Changes in the photospheres of F3V to M0V stars★
Max-Planck-Institut für Sonnensystemforschung,
Justus-von-Liebig Weg 3,
37077
Göttingen,
Germany
e-mail: bhatia@mps.mpg.de
Received:
20
March
2023
Accepted:
3
November
2023
Context. Some of the quiet solar magnetic flux could be attributed to a small-scale dynamo (SSD) operating in the convection zone. An SSD operating in cool main-sequence stars is expected to affect the atmospheric structure, in particular, the convection, and should have observational signatures.
Aims. We investigate the distribution of SSD magnetic fields and their effect on bolometric intensity characteristics, vertical velocity, and spatial distribution of the kinetic energy (KE) and magnetic energy (ME) in the lower photosphere of different spectral types.
Methods. We analyzed the SSD and purely hydrodynamic simulations of the near surface layers of F3V, G2V, K0V, and M0V stars. We compared the time-averaged distributions and power spectra in SSD setups relative to the hydrodynamic setup. The properties of the individual magnetic fields are also considered.
Results. The probability density functions with a field strength at the τ = 1 surface are quite similar for all cases. The M0V star displays the strongest fields, but relative to the gas pressure, the fields on the F3V star reach the highest values. In all stars, the horizontal field is stronger than the vertical field in the middle photosphere, and this excess becomes increasingly prominent toward later spectral types. These fields result in a decrease in the upflow velocities and a slight decrease in granule size, and also lead to formation of bright points in intergranular lanes. The spatial distribution of the KE and ME is also similar for all cases, implying that important scales are proportional to the pressure scale height.
Conclusions. The SSD fields have rather similar effects on the photospheres of cool main-sequence stars: a significant reduction in convective velocities, as well as a slight reduction in granule size and a concentration of the field to kilogauss levels in intergranular lanes that is associated with the formation of bright points. The distribution of the field strengths and energies is also rather similar.
Key words: convection / dynamo / stars: atmospheres / stars: late-type / stars: magnetic fields
Movies associated with Figs. 8 and 9 are available at https://www.aanda.org
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article is published in open access under the Subscribe to Open model.
Open Access funding provided by Max Planck Society.
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