2010, Strassmeier, K.G., Granzer, T., Weber, M., Woche, M., Popow, E., Jrvinen, A., Bartus, J., Bauer, S.-M., Dionies, F., Fechner, T., Bittner, W., Paschke, J.

The Astrophysical Institute Potsdam (AIP) and the Instituto de Astrofísica de Canarias (IAC) inaugurated the robotic telescopes STELLA-I and STELLA-II (STELLar Activity) on Tenerife on May 18, 2006. The observatory is located on the Izaa ridge at an elevation of 2400m near the German Vacuum Tower Telescope. STELLA consists of two 1.2m alt-az telescopes. One telescope fiber feeds a bench-mounted high-resolution echelle spectrograph while the other telescope feeds a wide-field imaging photometer. Both scopes work autonomously by means of artificial intelligence. Not only that the telescopes are automated, but the entire observatory operates like a robot, and does not require any human presence on site. Copyright © 2010 Klaus G. Strassmeier et al.

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.

2020, Warmuth, A., Önel, H., Mann, G., Rendtel, J., Strassmeier, K.G., Denker, C., Hurford, G.J., Krucker, S., Anderson, J., Bauer, S.-M., Bittner, W., Dionies, F., Paschke, J., Plüschke, D., Sablowski, D.P., Schuller, F., Senthamizh Pavai, V., Woche, M., Casadei, D., Kögl, S., Arnold, N.G., Gröbelbauer, H.-P., Schori, D., Wiehl, H.J., Csillaghy, A., Grimm, O., Orleanski, P., Skup, K.R., Bujwan, W., Rutkowski, K., Ber, K.

The Spectrometer/Telescope for Imaging X-rays (STIX) is a remote sensing instrument on Solar Orbiter that observes the hard X-ray bremsstrahlung emission of solar flares. This paper describes the STIX Aspect System (SAS), a subunit that measures the pointing of STIX relative to the Sun with a precision of ±4′′, which is required to accurately localize the reconstructed X-ray images on the Sun. The operating principle of the SAS is based on an optical lens that images the Sun onto a plate that is perforated by small apertures arranged in a cross-shaped configuration of four radial arms. The light passing through the apertures of each arm is detected by a photodiode. Variations of spacecraft pointing and of distance from the Sun cause the solar image to move over different apertures, leading to a modulation of the measured lightcurves. These signals are used by ground analysis to calculate the locations of the solar limb, and hence the pointing of the telescope.

2010, Granzer, T., Weber, M., Strassmeier, K.G.

Since May 2006, the two STELLA robotic telescopes at the Izaa observatory in Tenerife, Spain, delivered an almost uninterrupted stream of scientific data. To achieve such a high level of autonomous operation, the replacement of all troubleshooting skills of a regular observer in software was required. Care must be taken on error handling issues and on robustness of the algorithms used. In the current paper, we summarize the approaches we followed in the STELLA observatory. Copyright © 2010 Thomas Granzer et al.

2009, Strassmeier, K.G.

Starspots are created by local magnetic fields on the surfaces of stars, just as sunspots. Their fields are strong enough to suppress the overturning convective motion and thus block or redirect the flow of energy from the stellar interior outwards to the surface and consequently appear as locally cool and therefore dark regions against an otherwise bright photosphere (Biermann in Astronomische Nachrichten 264:361, 1938; Z Astrophysik 25:135, 1948). As such, starspots are observable tracers of the yet unknown internal dynamo activity and allow a glimpse into the complex internal stellar magnetic field structure. Starspots also enable the precise measurement of stellar rotation which is among the key ingredients for the expected internal magnetic topology. But whether starspots are just blown-up sunspot analogs, we do not know yet. This article is an attempt to review our current knowledge of starspots. A comparison of a white-light image of the Sun (G2V, 5 Gyr) with a Doppler image of a young solar-like star (EK Draconis; G1.5V, age 100 Myr, rotation 10 × Ω Sun) and with a mean-field dynamo simulation suggests that starspots can be of significantly different appearance and cannot be explained with a scaling of the solar model, even for a star of same mass and effective temperature. Starspots, their surface location and migration pattern, and their link with the stellar dynamo and its internal energy transport, may have far reaching impact also for our understanding of low-mass stellar evolution and formation. Emphasis is given in this review to their importance as activity tracers in particular in the light of more and more precise exoplanet detections around solar-like, and therefore likely spotted, host stars. © 2009 Springer-Verlag.

2020, Hansen, C.J., Koch, A., Mashonkina, L., Magg, M., Bergemann, M., Sitnova, T., Gallagher, A.J., Ilyin, I., Caffau, E., Zhang, H.W., Strassmeier, K.G., Klessen, R.S.

A long sought after goal using chemical abundance patterns derived from metal-poor stars is to understand the chemical evolution of the Galaxy and to pin down the nature of the first stars (Pop III). Metal-poor, old, unevolved stars are excellent tracers as they preserve the abundance pattern of the gas from which they were born, and hence they are frequently targeted in chemical tagging studies. Here, we use a sample of 14 metal-poor stars observed with the high-resolution spectrograph called the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) to derive abundances of 32 elements (34 including upper limits). We present well-sampled abundance patterns for all stars obtained using local thermodynamic equilibrium (LTE) radiative transfer codes and one-dimensional (1D) hydrostatic model atmospheres. However, it is currently well-known that the assumptions of 1D and LTE may hide several issues, thereby introducing biases in our interpretation as to the nature of the first stars and the chemical evolution of the Galaxy. Hence, we use non-LTE (NLTE) and correct the abundances using three-dimensional model atmospheres to present a physically more reliable pattern. In order to infer the nature of the first stars, we compare unevolved, cool stars, which have been enriched by a single event (“mono-enriched”), with a set of yield predictions to pin down the mass and energy of the Pop III progenitor. To date, only few bona fide second generation stars that are mono-enriched are known. A simple χ2-fit may bias our inferred mass and energy just as much as the simple 1D LTE abundance pattern, and we therefore carried out our study with an improved fitting technique considering dilution and mixing. Our sample presents Carbon Enhanced Metal-Poor (CEMP) stars, some of which are promising bona fide second generation (mono-enriched) stars. The unevolved, dwarf BD+09_2190 shows a mono-enriched signature which, combined with kinematical data, indicates that it moves in the outer halo and likely has been accreted onto the Milky Way early on. The Pop III progenitor was likely of 25.5 M⊙ and 0.6 foe (0.6 1051 erg) in LTE and 19.2 M⊙ and 1.5 foe in NLTE, respectively. Finally, we explore the predominant donor and formation site of the rapid and slow neutron-capture elements. In BD-10_3742, we find an almost clean r-process trace, as is represented in the star HD20, which is a “metal-poor Sun benchmark” for the r-process, while TYC5481-00786-1 is a promising CEMP-r/-s candidate that may be enriched by an asymptotic giant branch star of an intermediate mass and metallicity.

2008, Strassmeier, K.G.

[no abstract available]