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A widely accepted explanation for the origin of the ubiquitous small-scale magnetic field observed on the solar surface is thepresence of a small-scale dynamo (SSD) operating in the sub-surface layers of the Sun. To shed light on the functioning of thisSSD, a number of numerical studies of a realistic solar atmosphere have been carried out in the past two decades, greatlyimproving our knowledge on how an SSD operates. Nevertheless, virtually no studies focused on SSD action on the surfaceof other main-sequence stars. This motivates the work reported here. Hydro and magneto-hydrodynamics simulations of a small partial volume encompassing the surface layers of F5V, G2V, K2V, and K8V main-sequence stars are carried out with theradiative magnetohydrodynamic CO5BOLD code, investigating how SSD action can amplify a tiny seed magnetic field. In particular, the growth rate of the magnetic to kinetic energy ratio is characterized in terms of the Reynolds and magnetic Reynolds numbers of the simulations, and of the effective temperature and surface gravity of each star. It is found that the small-scale dynamo operating in the K2V simulation is the fastest in amplifying the magnetic energy among the four cases considered here. However, similar saturation values of the magnetic to kinetic energy ratio, of about 1%, are found at the surface for all the four stars. Ultimately, we investigate the spatial structure of the magnetic field resulting from SSD action and how it interacts with the plasma in the stellar atmospheres.

Full list of authors: Noda, C. Quintero; Schlichenmaier, R.; Bellot Rubio, L. R.; Lofdahl, M. G.; Khomenko, E.; Leenaarts, J.; Kuckein, C.; Gonzalez Manrique, S. J.; Gunar, S.; Nelson, C. J.; Rodriguez, J. de la Cruz; Tziotziou, K.; Tsiropoula, G.; Aulanier, G.; Aboudarham, J.; Allegri, D.; Alsina Ballester, E.; Amans, J. P.; Asensio Ramos, A.; Bailen, F. J.; Balaguer, M.; Baldini, V; Balthasar, H.; Barata, T.; Barczynski, K.; Barreto Cabrera, M.; Baur, A.; Bechet, C.; Beck, C.; Belio-Asin, M.; Bello-Gonzalez, N.; Belluzzi, L.; Bentley, R. D.; Berdyugina, S., V; Berghmans, D.; Berlicki, A.; Berrilli, F.; Berkefeld, T.; Bettonvil, F.; Bianda, M.; Bienes Perez, J.; Bonaque-Gonzalez, S.; Brajsa, R.; Bommier, V; Bourdin, P-A; BurgosMartin, J.; Calchetti, D.; Calcines, A.; Calvo Tovar, J.; Campbell, R. J.; Carballo-Martin, Y.; Carbone, V; Carlin, E. S.; Carlsson, M.; Castro Lopez, J.; Cavaller, L.; Cavallini, F.; Cauzzi, G.; Cecconi, M.; Chulani, H. M.; Cirami, R.; Consolini, G.; Coretti, I; Cosentino, R.; Cozar-Castellano, J.; Dalmasse, K.; Danilovic, S.; Ovelar, M. De Juan; Del Moro, D.; del Pino Aleman, T.; del Toro Iniesta, J. C.; Denker, C.; Dhara, S. K.; Di Marcantonio, P.; Baso, C. J. Diaz; Diercke, A.; Dineva, E.; Diaz-Garcia, J. J.; Doerr, H-P; Doyle, G.; Erdelyi, R.; Ermolli, I; Escobar Rodriguez, A.; Esteban Pozuelo, S.; Faurobert, M.; Felipe, T.; Feller, A.; Feijoo Amoedo, N.; Femenia Castella, B.; Fernandes, J.; Ferro Rodriguez, I; Figueroa, I; Fletcher, L.; Franco Ordovas, A.; Gafeira, R.; Gardenghi, R.; Gelly, B.; Giorgi, F.; Gisler, D.; Giovannelli, L.; Gonzalez, F.; Gonzalez, J. B.; Gonzalez-Cava, J. M.; Gonzalez Garcia, M.; Gomory, P.; Gracia, F.; Grauf, B.; Greco, V; Grivel, C.; Guerreiro, N.; Guglielmino, S. L.; Hammerschlag, R.; Hanslmeier, A.; Hansteen, V; Heinzel, P.; Hernandez-Delgado, A.; Hernandez Suarez, E.; Hidalgo, S. L.; Hill, F.; Hizberger, J.; Hofmeister, S.; Jagers, A.; Janett, G.; Jarolim, R.; Jess, D.; Jimenez Mejias, D.; Jolissaint, L.; Kamlah, R.; Kapitan, J.; Kasparova, J.; Keller, C. U.; Kentischer, T.; Kiselman, D.; Kleint, L.; Klvana, M.; Kontogiannis, I; Krishnappa, N.; Labrosse, N.; Lagg, A.; Degl'Innocenti, E. Landi; Langlois, M.; Lafon, M.; Laforgue, D.; Le Men, C.; Lepori, B.; Lepreti, F.; Lindberg, B.; Lilje, P. B.; Ariste, A. Lopez; Lopez Fernandez, V. A.; Lopez Jimenez, A. C.; Lopez Lopez, R.; Sainz, R. Manso; Marassi, A.; Marco de la Rosa, J.; Marino, J.; Marrero, J.; Martin, A.; Martin Galvez, A.; Martin Hernando, Y.; Masciadri, E.; MartinezGonzalez, M.; Matta-Gomez, A.; Mato, A.; Mathioudakis, M.; Matthews, S.; Mein, P.; Merlos Garcia, F.; Moity, J.; Montilla, I; Molinaro, M.; Molodij, G.; Montoya, L. M.; Munari, M.; Murabito, M.; Nunez Cagigal, M.; Oliviero, M.; Orozco Suarez, D.; Ortiz, A.; Padilla-Hernandez, C.; Paez Mana, E.; Paletou, F.; Pancorbo, J.; Pastor Canedo, A.; Yabar, A. Pastor; Peat, A. W.; Pedichini, F.; Peixinho, N.; Penate, J.; Perez de Taoro, A.; Peter, H.; Petrovay, K.; Piazzesi, R.; Pietropaolo, E.; Pleier, O.; Poedts, S.; Potzi, W.; Podladchikova, T.; Prieto, G.; Quintero Nehrkorn, J.; Ramelli, R.; Ramos Sapena, Y.; Rasilla, J. L.; Reardon, K.; Rebolo, R.; Regalado Olivares, S.; Reyes Garcia-Talavera, M.; Riethmuller, T. L.; Rimmele, T.; Rodriguez Delgado, H.; Rodriguez Gonzalez, N.; Rodriguez-Losada, J. A.; Rodriguez Ramos, L. F.; Romano, P.; Roth, M.; vander Voort, L. Rouppe; Rudawy, P.; Ruiz de Galarreta, C.; Rybak, J.; Salvade, A.; Sanchez-Capuchino, J.; Sanchez Rodriguez, M. L.; Sangiorgi, M.; Sayede, F.; Scharmer, G.; Scheiffelen, T.; Schmidt, W.; Schmieder, B.; Scire, C.; Scuderi, S.; Siegel, B.; Sigwarth, M.; Simoes, P. J. A.; Snik, F.; Sliepen, G.; Sobotka, M.; Socas-Navarro, H.; Sola La Serna, P.; Solanki, S. K.; Soler Trujillo, M.; Soltau, D.; Sordini, A.; Sosa Mendez, A.; Stangalini, M.; Steiner, O.; Stenflo, J. O.; Stepan, J.; Strassmeier, K. G.; Sudar, D.; Suematsu, Y.; Sutterlin, P.; Tallon, M.; Temmer, M.; Tenegi, F.; Tritschler, A.; Trujillo Bueno, J.; Turchi, A.; Utz, D.; van Harten, G.; VanNoort, M.; van Werkhoven, T.; Vansintjan, R.; Vaz Cedillo, J. J.; Vega Reyes, N.; Verma, M.; Veronig, A. M.; Viavattene, G.; Vitas, N.; Vogler, A.; von der Luhe, O.; Volkmer, R.; Waldmann, T. A.; Walton, D.; Wisniewska, A.; Zeman, J.; Zeuner, F.; Zhang, L. Q.; Zuccarello, F.; Collados, M.--This is an 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., The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operating in visible and near-infrared wavelengths: the Swedish 1m Solar Telescope, the German Vacuum Tower Telescope and GREGOR, the French Télescope Héliographique pour l’Étude du Magnétisme et des Instabilités Solaires, and the Dutch Open Telescope. With its 4.2 m primary mirror and an open configuration, EST will become the most powerful European ground-based facility to study the Sun in the coming decades in the visible and near-infrared bands. EST uses the most innovative technological advances: the first adaptive secondary mirror ever used in a solar telescope, a complex multi-conjugate adaptive optics with deformable mirrors that form part of the optical design in a natural way, a polarimetrically compensated telescope design that eliminates the complex temporal variation and wavelength dependence of the telescope Mueller matrix, and an instrument suite containing several (etalon-based) tunable imaging spectropolarimeters and several integral field unit spectropolarimeters. This publication summarises some fundamental science questions that can be addressed with the telescope, together with a complete description of its major subsystems. © C. Q. Noda et al. 2022., C.Q.N. was supported by the EST Project Office, funded by the Canary Islands Government (file SD 17/01) under a direct grant awarded to the IAC on ground of public interest. This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreements No 739500 (PRE-EST) and 653982 (GREST). This project was supported by the European Commission’s FP7 Capacities Programme under Grant Agreements No 212482 (EST Design Study) and No. 312495 (SOLARNET). It was also supported by the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No. 824135 (SOLARNET). This work has been partially funded by the Spanish Ministry of Science and Innovation through project RTI2018-096886-B-C51, including a percentage from FEDER funds, and through the Centro de Excelencia Severo Ochoa grant SEV-2017-0709 awarded to the Instituto de Astrofísica de Andalucía in the period 2018-2022. The EST preparatory phase was supported by a grant for research infrastructures of national importance from the Swedish Research Council (registration number 2017-00625). J.J. was supported by the Ministry of Education, Youth and Sports of the Czech Republic through the EST-CZ project (LM2018095). C.K. acknowledges funding received from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 895955. Queen’s University Belfast acknowledges support from the Science and Technology Facilities Council (STFC) under grant No. ST/V003739/1. This work was supported by Fundação para a Ciência e a Tecnologia (FCT) through the research grants [UID/FIS/04434/2019], UIDB/04434/2020, UIDP/04434/2020, UIDB/00611/2020 and UIDP/00611/2020. This work was partly funded by a grant of the Austrian Science Fund (FWF): P 32958-N. J.C.R., C.J.D.B. and A.P.Y. gratefully acknowledge financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (SUNMAG, grant agreement 759548). J.A. was supported by Centre National d’Etudes Spatiales (CNES). G.A., M.C., L.F., V.H., A.O. and L.R.V.V acknowledge support by the Research Council of Norway through its Centres of Excellence scheme, project number 262622. L.B., M.B., R.R. acknowledge State Secretariat for Education, Research, and Innovation (SERI), Canton Ticino and Swiss National Science Foundation (grants 200020_184952, 200021_175997, CRSII5_180238) for the financial support. R. Brajša and D. Sudar acknowledge the support by the Croatian Science Foundation under project 7549 ‘Millimeter and submillimeter observations of the solar chromosphere with ALMA’. The NSO is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. The work of A.B. was partially supported by the programme ‘Excellence Initiative – Research University’ for years 2020–2026 for University of Wrocław, project no. BPIDUB.4610.15.2021.KP.B. E.S.C. acknowledges financial support from the Spanish Ministry of Science and Innovation (MICINN) through the Spanish State Research Agency, under Severo Ochoa Centres of Excellence Programme 2020-2023 (CEX2019-000920-S). L.F. and N.L. would like to acknowledge support from UK Research and Innovation Science and Technology Facilities Council grants ST/L006200/1 and ST/T000422/1. J.F. acknowledges visiting facilities at Rosseland Centre for Solar Physics (University of Oslo), in 2019. P. Gömöry, A.K. and J.R. were supported by the Science Grant Agency project VEGA 2/0048/20. I. Kontogiannis is supported by KO 6283/2-1 of the Deutsche Forschungsgemeinschaft (DFG). C.J.N. is thankful to the Science and Technology Facilities Council (STFC), for support received through grant ST/T00021X/1, and ESA, for support as an ESA Research Fellow. K.P. was supported by the Hungarian National Research, Development and Innovation Fund (grants no. NKFI K-128384 and TKP2021-NKTA-64). P.J.A. Simões acknowledges support from CNPq (contract 307612/2019-8). J.T.B. acknowledges the funding received from the European Research Council (ERC) under de European Union’s Horizon 2020 research and innovation programme (ERC Advanced Grant Agreement No. 742265). M.V. is supported by VE 1112/1-1 of the Deutsche Forschungsgemeinschaft (DFG). L.Q.Z. acknowledges that this work was supported by the National Natural Science Foundation of China (Grant No. 11727805, No. 1210030348). F.Z. acknowledges that this work was supported by the Italian MIUR-PRIN grant 2017APKP7T and by the Università degli Studi di Catania (Piano per la Ricerca Università di Catania 2020-2022, Linea di intervento 2).

Context. As a universally accepted definition of a vortex has not yet been established, the community lacks an unambiguous and rigorous method for identifying vortices in fluid flows. Such a method would be useful for conducting robust statistical studies on vortices in highly dynamical and turbulent systems such as the solar atmosphere. Aims. We aim to develop an innovative and robust automated methodology for the identification of vortices based on local and global characteristics of the flow, while avoiding the use of a threshold that could potentially prevent the detection of weak vortices in the process. Methods. We present a new method that combines the rigor of mathematical criteria with the global perspective of morphological techniques. The core of the method consists of an estimation of the center of rotation for every point of the flow that presents some degree of curvature in its neighborhood. For this purpose, we employed the Rortex criterion and combined it with morphological considerations of the velocity field. We then identified coherent vortical structures based on clusters of estimated centers of rotation. Results. We demonstrate that the Rortex is a more reliable criterion than the swirling strength and the vorticity for the extraction of physical information from vortical flows, because it measures the rigid-body rotational part of the flow alone and is not biased by the presence of pure or intrinsic shears. We show that the method performs well in the context of a simplistic test case composed of two Lamb-Oseen vortices. We combined the proposed method with a state-of-the-art clustering algorithm to build an automated vortex identification algorithm. The algorithm was applied to an artificial flow composed of multiple Lamb- Oseen vortices, with a random noisy background, and to the turbulent flow of a simulated magneto-hydrodynamical Orszag-Tang vortex test. The results demonstrate the reliability and accuracy of the method. Conclusions. The present automated vortex identification method can be considered a new tool for the detection and study of vortices in dynamical and turbulent (magneto)hydrodynamical flows. By applying the implemented algorithm to numerical simulations and observational data, as well as comparing it to existing detection methods, we seek to successively improve the reliability of the detections and, ultimately, our knowledge on swirling motions in the solar, stellar, and planetary atmospheres.

There has been tremendous progress in the degree of realism of three-dimensional radiation magneto-hydrodynamic simulations of the solar atmosphere in the past decades. Four of the most frequently used numerical codes are Bifrost, CO5BOLD, MANCHA3D, and MURaM. Here we test and compare the wave propagation characteristics in model runs from these four codes by measuring the dispersion relation of acoustic-gravity waves at various heights. We find considerable differences between the various models. The height dependence of wave power, in particular of high-frequency waves, varies by up to two orders of magnitude between the models, and the phase difference spectra of several models show unexpected features, including $\pm180^\circ$ phase jumps., Comment: 19 pages, 15 figures

Three kinds of magnetic couplings in the quiet solar atmosphere are highlighted and discussed, all fundamentally connected to the Lorentz force. First the coupling of the convecting and overshooting fluid in the surface layers of the Sun with the magnetic field. Here, the plasma motion provides the dominant force, which shapes the magnetic field and drives the surface dynamo. Progress in the understanding of the horizontal magnetic field is summarized and discussed. Second, the coupling between acoustic waves and the magnetic field, in particular the phenomenon of wave conversion and wave refraction. It is described how measurements of wave travel times in the atmosphere can provide information about the topography of the wave conversion zone, i.e., the surface of equal Alfv\'en and sound speed. In quiet regions, this surface separates a highly dynamic magnetic field with fast moving magnetosonic waves and shocks around and above it from the more slowly evolving field of high-beta plasma below it. Third, the magnetic field also couples to the radiation field, which leads to radiative flux channeling and increased anisotropy in the radiation field. It is shown how faculae can be understood in terms of this effect. The article starts with an introduction to the magnetic field of the quiet Sun in the light of new results from the Hinode space observatory and with a brief survey of measurements of the turbulent magnetic field with the help of the Hanle effect., Comment: To appear in "Magnetic Coupling between the Interior and the Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 2009

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The piezoelectric properties of the bismuth titanate niobate Bi7Ti4NbO21 have been studied. The two phase transitions at 677 degrees and 856 degrees C are analyzed based on the measured piezoelectric properties. It is shown that the Bi7Ti4NbO21 compound is a ferroelectric until 856 degrees C. Bi3TiNbO9 clusters are shown to exist within Bi7Ti4NbO21 grains. These clusters may be responsible for the small additional piezoelectric activity of the studied material at temperatures higher than 856 degrees C.