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- ItemThe STELLA robotic observatory on tenerife(New York : Hindawi Publishing Corporation, 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 AstrofÃsica 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.
- ItemThree years of experience with the STELLA robotic observatory(New York : Hindawi Publishing Corporation, 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.
- ItemStarspots(Berlin : Springer Verlag, 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.
- ItemThe STIX Aspect System (SAS): The Optical Aspect System of the Spectrometer/Telescope for Imaging X-Rays (STIX) on Solar Orbiter(Dordrecht [u.a.] : Springer Science + Business Media B.V, 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.
- ItemEntwurf, Bau und Betrieb eines hochauflösenden optischen Spektralpolarimeters für das LBT - Large Binocular Telescope in Arizona : Schlussbericht für das BMBF-Vorhaben(Hannover : Technische Informationsbibliothek (TIB), 2008) Strassmeier, K.G.[no abstract available]