2021, Ellwarth, M., Fischer, C.E., Vitas, N., Schmiz, S., Schmidt, W.

Context. Exploding granules have drawn renewed interest because of their interaction with the magnetic field (either emerging or already present). Especially the newly forming downflow lanes developing in their centre seem to be eligible candidates for the intensification of magnetic fields. We analyse spectroscopic data from two different instruments in order to study the intricate velocity pattern within the newly forming downflow lanes in detail. Aims. We aim to examine general properties of a number of exploding granules, such as their lifetime and extend. To gain a better understanding of the formation process of the developing intergranular lane in exploding granules, we study the temporal evolution and height dependence of the line-of-sight velocities at their formation location. Additionally, we search for evidence that exploding granules act as acoustic sources. Methods. We investigated the evolution of several exploding granules using data taken with the Interferometric Bidimensional Spectrometer and the Imaging Magnetograph eXperiment. Velocities for different heights of the solar atmosphere were determined by computing bisectors of the Fe I 6173.0 Å and the Fe I 5250.2 Å lines. We performed a wavelet analysis to study the intensity and velocity oscillations within and around exploding granules. We also compared our observational findings with predictions of numerical simulations. Results. Exploding granules have significantly longer lifetimes (10 to 15 min) than regular granules. Exploding granules larger than 3.8″ form an independent intergranular lane during their decay phase, while smaller granules usually fade away or disappear into the intergranular area (we find only one exception of a smaller exploding granule that also forms an intergranular lane). For all exploding granules that form a new intergranular downflow lane, we find a temporal height-dependent shift with respect to the maximum of the downflow velocity. Our suggestion that this results from a complex atmospheric structure within the newly forming downflow lane is supported by the comparison with synthesised profiles inferred from the simulations. We found an enhanced wavelet power with periods between 120 s to 190 s seen in the intensity and velocity oscillations of high photospheric or chromospheric spectral lines in the region of the dark core of an exploding granule. © M. Ellwarth et al. 2021.

2015, Probst, R.A., Wang, L., Doerr, H.-P., Steinmetz, T., Kentischer, T.J., Zhao, G., Hänsch, T.W., Udem, T., Holzwarth, R., Schmidt, W.

We investigate a new scheme for astronomical spectrograph calibration using the laser frequency comb at the Solar Vacuum Tower Telescope on Tenerife. Our concept is based upon a single-mode fiber channel, that simultaneously feeds the spectrograph with comb light and sunlight. This yields nearly perfect spatial mode matching between the two sources. In combination with the absolute calibration provided by the frequency comb, this method enables extremely robust and accurate spectroscopic measurements. The performance of this scheme is compared to a sequence of alternating comb and sunlight, and to absorption lines from Earth's atmosphere. We also show how the method can be used for radial-velocity detection by measuring the well-explored 5 min oscillations averaged over the full solar disk. Our method is currently restricted to solar spectroscopy, but with further evolving fiber-injection techniques it could become an option even for faint astronomical targets.

2010, Berkefeld, T., Schmidt, W., Soltau, D., Bell, A., Doerr, H.P., Feger, B., Friedlein, R., Gerber, K., Heidecke, F., Kentischer, T., von der Lühe, O., Sigwarth, M., Wälde, E., Barthol, P., Deutsch, W., Gandorfer, A., Germerott, D., Grauf, B., Meller, R., Álvarez-Herrero, A., Knölker, M., Pillet, V.M., Solanki, S.K., Title, A.M.

This paper describes the wave-front correction system developed for the Sunrise balloon telescope, and it provides information about its in-flight performance. For the correction of low-order aberrations, a Correlating Wave-Front Sensor (CWS) was used. It consisted of a six-element Shack - Hartmann wave-front sensor (WFS), a fast tip-tilt mirror for the compensation of image motion, and an active telescope secondary mirror for focus correction. The CWS delivered a stabilized image with a precision of 0.04 arcsec (rms), whenever the coarse pointing was better than ± 45 arcsec peak-to-peak. The automatic focus adjustment maintained a focus stability of 0.01 waves in the focal plane of the CWS. During the 5.5 day flight, good image quality and stability were achieved during 33 hours, containing 45 sequences, which lasted between 10 and 45 min. © 2010 The Author(s).

2020, Solanki, S.K., del Toro Iniesta, J.C., Woch, J., Gandorfer, A., Hirzberger, J., Alvarez-Herrero, A., Appourchaux, T., Martínez Pillet, V., Pérez-Grande, I., Sanchis Kilders, E., Schmidt, W., Garranzo-García, D., Laguna, H., Martín, J.A., Navarro, R., Villanueva, J., Núñez Peral, A., Royo, M., Sánchez, A., Silva-López, M., Fourmond, J.-J., Berkefeld, Th., Ruiz de Galarreta, C., Bouzit, M., Hervier, V., Le Clec'h, J.C., Szwec, N., Chaigneau, M., Buttice, V., Volkmer, R., Dominguez-Tagle, C., Philippon, A., Baumgartner, J., Boumier, P., Le Cocguen, R., Baranjuk, G., Bell, A., Heidecke, F., Maue, T., Blanco Rodríguez, J., Nakai, E., Scheiffelen, T., Sigwarth, M., Soltau, D., Domingo, V., Fiethe, B., Ferreres Sabater, A., Gasent Blesa, J.L., Rodríguez Martínez, P., Osorno Caudel, D., Bosch, J., Casas, A., Carmona, M., Gómez Cama, J.M., Herms, A., Roma, D., Guan, Y., Alonso, G., Gómez-Sanjuan, A., Piqueras, J., Torralbo, I., Lange, T., Michel, H., Michalik, H., Bonet, J.A., Fahmy, S., Müller, D., Zouganelis, I., Deutsch, W., Busse, D., Fernandez-Rico, G., Grauf, B., Gizon, L., Heerlein, K., Kolleck, M., Lagg, A., Meller, R., Müller, R., Schühle, U., Staub, J., Enge, R., Albert, K., Alvarez Copano, M., Beckmann, U., Bischoff, J., Frahm, S., Germerott, D., Guerrero, L., Löptien, B., Meierdierks, T., Oberdorfer, D., Papagiannaki, I., Ramanath, S., Bellot Rubio, L.R., Schou, J., Werner, S., Yang, D., Zerr, A., Bergmann, M., Bochmann, J., Heinrichs, J., Meyer, S., Monecke, M., Müller, M.-F., Cobos Carracosa, J.P., Sperling, M., Álvarez García, D., Aparicio, B., Balaguer Jiménez, M., Girela, F., Hernández Expósito, D., Herranz, M., Labrousse, P., López Jiménez, A., Orozco Suárez, D., Ramos, J.L., Barandiarán, J., Vera, I., Bastide, L., Campuzano, C., Cebollero, M., Dávila, B., Fernández-Medina, A., García Parejo, P.

This paper describes the Polarimetric and Helioseismic Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and helioseismology instrument to observe the Sun from outside the Sun-Earth line. It is the key instrument meant to address the top-level science question: How does the solar dynamo work and drive connections between the Sun and the heliosphere? SO/PHI will also play an important role in answering the other top-level science questions of Solar Orbiter, as well as hosting the potential of a rich return in further science. SO/PHI measures the Zeeman effect and the Doppler shift in the FeI 617.3nm spectral line. To this end, the instrument carries out narrow-band imaging spectro-polarimetry using a tunable LiNbO_3 Fabry-Perot etalon, while the polarisation modulation is done with liquid crystal variable retarders (LCVRs). The line and the nearby continuum are sampled at six wavelength points and the data are recorded by a 2kx2k CMOS detector. To save valuable telemetry, the raw data are reduced on board, including being inverted under the assumption of a Milne-Eddington atmosphere, although simpler reduction methods are also available on board. SO/PHI is composed of two telescopes; one, the Full Disc Telescope (FDT), covers the full solar disc at all phases of the orbit, while the other, the High Resolution Telescope (HRT), can resolve structures as small as 200km on the Sun at closest perihelion. The high heat load generated through proximity to the Sun is greatly reduced by the multilayer-coated entrance windows to the two telescopes that allow less than 4% of the total sunlight to enter the instrument, most of it in a narrow wavelength band around the chosen spectral line.

2013, Wiegelmann, T., Solanki, S.K., Borrero, J.M., Peter, H., Barthol, P., Gandorfer, A., Martínez Pillet, V., Schmidt, W., Knölker, M.

Observations with the balloon-borne Sunrise/Imaging Magnetograph eXperiment (IMaX) provide high spatial resolution (roughly 100 km at disk center) measurements of the magnetic field in the photosphere of the quiet Sun. To investigate the magnetic structure of the chromosphere and corona, we extrapolate these photospheric measurements into the upper solar atmosphere and analyze a 22-minute long time series with a cadence of 33 seconds. Using the extrapolated magnetic-field lines as tracer, we investigate temporal evolution of the magnetic connectivity in the quiet Sun’s atmosphere. The majority of magnetic loops are asymmetric in the sense that the photospheric field strength at the loop foot points is very different. We find that the magnetic connectivity of the loops changes rapidly with a typical connection recycling time of about 3±1 minutes in the upper solar atmosphere and 12±4 minutes in the photosphere. This is considerably shorter than previously found. Nonetheless, our estimate of the energy released by the associated magnetic-reconnection processes is not likely to be the sole source for heating the chromosphere and corona in the quiet Sun.

2011, Gandorfer, A., Grauf, B., Barthol, P., Riethmüller, T.L., Solanki, S.K., Chares, B., Deutsch, W., Ebert, S., Feller, A., Germerott, D., Heerlein, K., Heinrichs, J., Hirche, D., Hirzberger, J., Kolleck, M., Meller, R., Müller, R., Schäfer, R., Tomasch, G., Knölker, M., Martínez Pillet, V., Bonet, J.A., Schmidt, W., Berkefeld, T., Feger, B., Heidecke, F., Soltau, D., Tischenberg, A., Fischer, A., Title, A., Anwand, H., Schmidt, E.

We describe the design of the Sunrise Filter Imager (SuFI) and the Image Stabilization and Light Distribution (ISLiD) unit onboard the Sunrise balloon borne solar observatory. This contribution provides the necessary information which is relevant to understand the instruments' working principles, the relevant technical data, and the necessary information about calibration issues directly related to the science data. © 2010 The Author(s).

2022, Quintero Noda, C., Schlichenmaier, R., Bellot Rubio, L.R., Löfdahl, M.G., Khomenko, E., Jurčák, J., Leenaarts, J., Kuckein, C., González Manrique, S.J., Gunár, S., Nelson, C.J., Giovannelli, L., González, F., González, J.B., González-Cava, J.M., González García, M., Gömöry, P., Gracia, F., Grauf, B., Greco, V., Grivel, C., de la Cruz Rodríguez, J., Guerreiro, N., Guglielmino, S.L., Hammerschlag, R., Hanslmeier, A., Hansteen, V., Heinzel, P., Hernández-Delgado, A., Hernández Suárez, E., Hidalgo, S.L., Hill, F., Tziotziou, K., Hizberger, J., Hofmeister, S., Jägers, A., Janett, G., Jarolim, R., Jess, D., Jiménez Mejías, D., Jolissaint, L., Kamlah, R., Kapitán, J., Tsiropoula, G., Kašparová, J., Keller, C.U., Kentischer, T., Kiselman, D., Kleint, L., Klvana, M., Kontogiannis, I., Krishnappa, N., Kučera, A., Labrosse, N., Aulanier, G., Lagg, A., Landi Degl’Innocenti, E., Langlois, M., Lafon, M., Laforgue, D., Le Men, C., Lepori, B., Lepreti, F., Lindberg, B., Lilje, P.B., Aboudarham, J., López Ariste, A., López Fernández, V.A., López Jiménez, A.C., López López, R., Manso Sainz, R., Marassi, A., Marco de la Rosa, J., Marino, J., Marrero, J., Martín, A., Allegri, D., Martín Gálvez, A., Martín Hernando, Y., Masciadri, E., Martínez González, M., Matta-Gómez, A., Mato, A., Mathioudakis, M., Matthews, S., Mein, P., Merlos García, F., Alsina Ballester, E., Moity, J., Montilla, I., Molinaro, M., Molodij, G., Montoya, L.M., Munari, M., Murabito, M., Núñez Cagigal, M., Oliviero, M., Orozco Suárez, D., Amans, J.P., Ortiz, A., Padilla-Hernández, C., Paéz Mañá, E., Paletou, F., Pancorbo, J., Pastor Cañedo, A., Pastor Yabar, A., Peat, A.W., Pedichini, F., Peixinho, N., Asensio Ramos, A., Peñate, J., Pérez de Taoro, A., Peter, H., Petrovay, K., Piazzesi, R., Pietropaolo, E., Pleier, O., Poedts, S., Pötzi, W., Podladchikova, T., Bailén, F.J., Prieto, G., Quintero Nehrkorn, J., Ramelli, R., Ramos Sapena, Y., Rasilla, J.L., Reardon, K., Rebolo, R., Regalado Olivares, S., Reyes García-Talavera, M., Riethmüller, T.L., Balaguer, M., Rimmele, T., Rodríguez Delgado, H., Rodríguez González, N., Rodríguez-Losada, J.A., Rodríguez Ramos, L.F., Romano, P., Roth, M., Rouppe van der Voort, L., Rudawy, P., Ruiz de Galarreta, C., Baldini, V., Rybák, J., Salvade, A., Sánchez-Capuchino, J., Sánchez Rodríguez, M.L., Sangiorgi, M., Sayède, F., Scharmer, G., Scheiffelen, T., Schmidt, W., Schmieder, B., Balthasar, H., Scirè, C., Scuderi, S., Siegel, B., Sigwarth, M., Simões, P.J.A., Snik, F., Sliepen, G., Sobotka, M., Socas-Navarro, H., Sola La Serna, P., Barata, T., Solanki, S. K., Soler Trujillo, M., Soltau, D., Sordini, A., Sosa Méndez, A., Stangalini, M., Steiner, O., Stenflo, J.O., Štěpán, J., Strassmeier, K.G., Barczynski, K., Sudar, D., Suematsu, Y., Sütterlin, P., Tallon, M., Temmer, M., Tenegi, F., Tritschler, A., Trujillo Bueno, J., Turchi, A., Utz, D., Barreto Cabrera, M., van Harten, G., van Noort, M., van Werkhoven, T., Vansintjan, R., Vaz Cedillo, J.J., Vega Reyes, N., Verma, M., Veronig, A.M., Viavattene, G., Vitas, N., Baur, A., Vögler, A., von der Lühe, O., Volkmer, R., Waldmann, T.A., Walton, D., Wisniewska, A., Zeman, J., Zeuner, F., Zhang, L.Q., Zuccarello, F., Béchet, C., Collados, M., Beck, C., Belío-Asín, M., Bello-González, N., Belluzzi, L., Bentley, R.D., Berdyugina, S.V., Berghmans, D., Berlicki, A., Berrilli, F., Berkefeld, T., Bettonvil, F., Bianda, M., Bienes Pérez, J., Bonaque-González, S., Brajša, R., Bommier, V., Bourdin, P.-A., Burgos Martín, J., Calchetti, D., Calcines, A., Calvo Tovar, J., Campbell, R.J., Carballo-Martín, Y., Carbone, V., Carlin, E.S., Carlsson, M., Castro López, J., Cavaller, L., Cavallini, F., Cauzzi, G., Cecconi, M., Chulani, H.M., Cirami, R., Consolini, G., Coretti, I., Cosentino, R., Cózar-Castellano, J., Dalmasse, K., Danilovic, S., De Juan Ovelar, M., Del Moro, D., del Pino Alemán, T., del Toro Iniesta, J. C., Denker, C., Dhara, S.K., Di Marcantonio, P., Díaz Baso, C.J., Diercke, A., Dineva, E., Díaz-García, J.J., Doerr, H.-P., Doyle, G., Erdelyi, R., Ermolli, I., Escobar Rodríguez, A., Esteban Pozuelo, S., Faurobert, M., Felipe, T., Feller, A., Feijoo Amoedo, N., Femenía Castellá, B., Fernandes, J., Ferro Rodríguez, I., Figueroa, I., Fletcher, L., Franco Ordovas, A., Gafeira, R., Gardenghi, R., Gelly, B., Giorgi, F., Gisler, D.

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.

2010, Barthol, P., Gandorfer, A., Solanki, S.K., Schüssler, M., Chares, B., Curdt, W., Deutsch, W., Feller, A., Germerott, D., Grauf, B., Heerlein, K., Hirzberger, J., Kolleck, M., Meller, R., Müller, R., Riethmüller, T.L., Tomasch, G., Knölker, M., Lites, B.W., Card, G., Elmore, D., Fox, J., Lecinski, A., Nelson, P., Summers, R., Watt, A., Martínez Pillet, V., Bonet, J.A., Schmidt, W., Berkefeld, T., Title, A.M., Domingo, V., Gasent Blesa, J.L., del Toro, Iniesta, J.C., López Jiménez, A., Álvarez-Herrero, A., Sabau-Graziati, L., Widani, C., Haberler, P., Härtel, K., Kampf, D., Levin, T., Pérez Grande, I., Sanz-Andrés, A., Schmidt, E.

The first science flight of the balloon-borne Sunrise telescope took place in June 2009 from ESRANGE (near Kiruna/Sweden) to Somerset Island in northern Canada. We describe the scientific aims and mission concept of the project and give an overview and a description of the various hardware components: the 1-m main telescope with its postfocus science instruments (the UV filter imager SuFI and the imaging vector magnetograph IMaX) and support instruments (image stabilizing and light distribution system ISLiD and correlating wavefront sensor CWS), the optomechanical support structure and the instrument mounting concept, the gondola structure and the power, pointing, and telemetry systems, and the general electronics architecture. We also explain the optimization of the structural and thermal design of the complete payload. The preparations for the science flight are described, including AIV and ground calibration of the instruments. The course of events during the science flight is outlined, up to the recovery activities. Finally, the in-flight performance of the instrumentation is discussed. © 2010 The Author(s).