Author name code: caligari ADS astronomy entries on 2022-09-14 author:"Caligari, Peter" ------------------------------------------------------------------------ Title: A retrospective of the GREGOR solar telescope in scientific literature Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.; Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.; Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa, M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.; Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann, T.; Wiehr, E.; Wittmann, A. D.; Woche, M. Bibcode: 2012AN....333..810D Altcode: 2012arXiv1210.3167D In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post-focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i.e., the final stages of commissioning and science verification. Taking stock of the various publications in peer-reviewed journals and conference proceedings also provides the ``historical'' context for the reference articles in this special issue of Astronomische Nachrichten/Astronomical Notes. Title: The GREGOR telescope control system Authors: Halbgewachs, C.; Caligari, P.; Glogowski, K.; Heidecke, F.; Knobloch, M.; Mustedanagic, M.; Volkmer, R.; Waldmann, T. A. Bibcode: 2012AN....333..840H Altcode: This article describes the architecture of the new GREGOR telescope and its instrument control system. A short summary is given on the communication structure between instruments and other devices during observation. Because of its importance to all instruments the main functions of the telescope control system are described in detail. Title: GREGOR telescope: start of commissioning Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S.; Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvana, M.; Kneer, F.; Lagg, A.; Popow, E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K. Bibcode: 2010SPIE.7733E..0KV Altcode: 2010SPIE.7733E..18V With the integration of a 1-meter Cesic primary mirror the GREGOR telescope pre-commissioning started. This is the first time, that the entire light path has seen sunlight. The pre-commissioning period includes testing of the main optics, adaptive optics, cooling system, and pointing system. This time was also used to install a near-infrared grating spectro-polarimeter and a 2D-spectropolarimeter for the visible range as first-light science instruments. As soon as the final 1.5 meter primary mirror is installed, commissioning will be completed, and an extended phase of science verification will follow. In the near future, GREGOR will be equipped with a multi-conjugate adaptive optics system that is presently under development at KIS. Title: GREGOR solar telescope: Design and status Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S. K.; Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Kneer, F.; Lagg, A.; Popow, E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G. Bibcode: 2010AN....331..624V Altcode: The integration and verification phase of the GREGOR telescope reached an important milestone with the installation of the interim 1 m SolarLite primary mirror. This was the first time that the entire light path had seen sunlight. Since then extensive testing of the telescope and its subsystems has been carried out. The integration and verification phase will culminate with the delivery and installation of the final 1.5 m Zerodur primary mirror in the summer of 2010. Observatory level tests and science verification will commence in the second half of 2010 and in 2011. This phase includes testing of the main optics, adaptive optics, cooling and pointing systems. In addition, assuming the viewpoint of a typical user, various observational modes of the GREGOR Fabry-Pérot Interferometer (GFPI), the Grating Infrared Spectrograph (GRIS), and high-speed camera systems will be tested to evaluate if they match the expectations and science requirements. This ensures that GREGOR will provide high-quality observations with its combination of (multi-conjugate) adaptive optics and advanced post-focus instruments. Routine observations are expected for 2012. Title: The control and data concept for the robotic solar telescope ChroTel Authors: Halbgewachs, C.; Bethge, Ch.; Caligari, P.; Elmore, D.; Kentischer, T. J.; Peter, H.; Sigwarth, M.; Schmidt, W. Bibcode: 2008SPIE.7019E..2TH Altcode: 2008SPIE.7019E..93H The solar telescope ChroTel is designed as a robotic telescope so that no user interaction is necessary for observation. The telescope will start tracking in the morning as soon as weather conditions are appropriate and will process a user defined observation routine until sunset. Weather conditions and system status are continuously monitored to close the telescope shutter in case of bad weather or to drive to the stow position in case of an error. The ChroTel control software was programmed in LabVIEW. Title: GREGOR: the New German Solar Telescope Authors: Balthasar, H.; von der Lühe, O.; Kneer, F.; Staude, J.; Volkmer, R.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Nicklas, H.; Popow, E.; Puschmann, K.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K.; Wittmann, A. Bibcode: 2007ASPC..368..605B Altcode: 2007arXiv0704.2693B GREGOR is a new open solar telescope with an aperture of 1.5 m. It replaces the former 45-cm Gregory Coudé telescope on the Canary island Tenerife. The optical concept is that of a double Gregory system. The main and the elliptical mirrors are made from a silicon-carbide material with high thermal conductivity. This is important to keep the mirrors on the ambient temperature avoiding local turbulence. GREGOR will be equipped with an adaptive optics system. The new telescope will be ready for operation in 2008. Post-focus instruments in the first stage will be a spectrograph for polarimetry in the near infrared and a 2-dimensional spectrometer based on Fabry-Pérot interferometers for the visible. Title: New high resolution solar telescope GREGOR Authors: Volkmer, R.; von der Lühe, O.; Kneer, F.; Staude, J.; Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaña, M.; Sobotka, M.; Nicklas, H.; Popow, E.; Puschmann, K. G.; Schmidt, W.; Soltau, D.; Strassmeier, K.; Wittmann, A. D. Bibcode: 2007msfa.conf...39V Altcode: The 1.5m solar telescope GREGOR is being constructed at Tenerife, Spain. Its purpose is to observe with high spatial and spectral resolution small-scale dynamic magnetic features on the Sun. The telescope is completely open with retractable dome and actively cooled primary mirror made of silicon carbide to minimize thermal effects on the image quality. After completion it will be one of the most powerful solar telescopes. This paper presents a general overview of the telescope characteristics and the current status. Title: The new 1.5m solar telescope GREGOR: first light and start of commissioning Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude, Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens; Heidecke, Frank; Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wittmann, Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka, Michal; Klvana, Miroslav; Collados, Manuel Bibcode: 2006SPIE.6267E..0WV Altcode: 2006SPIE.6267E..29V The integration of the three main silicon carbide mirrors into the new 1.5 m solar telescope GREGOR at Izana on Tenerife, Spain is planned during 2006. We expect first light at the end of 2006. A progress report about integration of the optics and mechanics and planning of the commissioning phase of the telescope and post focus instruments will be presented at the meeting. The GREGOR telescope is build by a consortium of the Kiepenheuer Institut fur Sonnenphysik in Freiburg, the Astrophysikalische Institut Potsdam, the Institut fur Astronomie Gottingen and additional national and international Partners. Title: The new 1.5 solar telescope GREGOR: progress report and results of performance tests Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude, Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens; Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wittmann, Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka, Michal; Klvana, Miroslav; Collados, Manuel Bibcode: 2005SPIE.5901...75V Altcode: The telescope structure including control system and the complete retractable dome of the new 1.5 m solar telescope GREGOR were assembled during 2004 at Izana on Tenerife, Spain. The GREGOR telescope is build by a consortium of the Kiepenheuer Institut fuer Sonnenphysik, the Astrophysikalische Institut Potsdam, the Institut fuer Astrophysik Goettingen and additional national and international Partners. Pointing, tracking and thermal tests were made to verify the proposed performance. The results of these tests and a progress report of the project will be presented. Title: Progress report of the 1.5 m solar telescope GREGOR Authors: Volkmer, Reiner; von der Lühe, Oskar F.; Kneer, Franz; Staude, Jürgen; Berkefeld, Thomas; Caligari, Peter; Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wiehr, Eberhardt; Wittmann, Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka, Michal; Klvana, Miroslav; Collados, Manuel Bibcode: 2004SPIE.5489..693V Altcode: GREGOR is the new 1.5 m solar telescope assembled on Tenerife, Spain, by the German consortium of the Kiepenheuer Institut fur Sonnenphysik, the Astronomischen Institut Potsdam, the Universitats-Sternwarte Gottingen and other national and international Partners. The refurbishment of the building is almost finished. The manufacturing of the telescope structure and the optics is still in progress. After the integration of the new complete retractable dome in July 2004 the telescope structure, optic and post focus instruments will be assembled during the rest of the year. First light is planned during May 2005. Title: Star Spot Patterns on Young Stars: Theoretical Approach (CD-ROM Directory: contribs/granzer2) Authors: Granzer, Th.; Caligari, P.; Schüssler, M.; Strassmeier, K. G. Bibcode: 2001ASPC..223.1232G Altcode: 2001csss...11.1232G No abstract at ADS Title: Distribution of starspots on cool stars. II. Pre-main-sequence and ZAMS stars between 0.4 Msun and 1.7 Msun Authors: Granzer, Th.; Schüssler, M.; Caligari, P.; Strassmeier, K. G. Bibcode: 2000A&A...355.1087G Altcode: We study the dynamics of magnetic flux tubes in young stars with masses between 0.4 Msun and 1.7 Msun and for rotation rates between 0.25 Omegasun and 63 Omegasun . The resulting latitudinal emergence patterns at the stellar surface are compared with observed distributions of starspots in stellar latitude. The stellar models considered cover the range of evolutionary stages from shortly after the Hayashi phase down to the ZAMS, i.e. from the classical and weak-line T Tauri stars to the alpha -Persei stars. We use numerical simulations to follow the evolution of magnetic flux tubes from their origin at the bottom of the convection zone up to near-surface layers. We find a strong increase of emergence latitude with increasing rotation rate, a moderate decrease with increasing stellar mass, and a stronger decrease with stellar age. At very early evolutionary stages, when the central radiative zone is still quite small, we find magnetic flux emergence both in low latitudes as well as in the polar areas. High-latitude emergence is predicted in slightly more evolved pre-main-sequence and young main-sequence stars, but truly polar spots on these stars require an additional transport mechanism acting after magnetic flux emergence at the surface, probably meridional circulation or poleward slip of the `anchored' part of the erupted flux tubes. We discuss our findings in the light of the results obtained from Doppler-imaging studies. Title: Emerging Flux Tubes in the Solar Convection Zone. II. The Influence of Initial Conditions Authors: Caligari, P.; Schüssler, M.; Moreno-Insertis, F. Bibcode: 1998ApJ...502..481C Altcode: Numerical simulations of rising magnetic flux tubes in the solar convection zone have contributed significantly to our understanding of the basic properties of sunspot groups. They have provided an important clue to the operation of the solar dynamo by predicting strong (super-equipartition) magnetic fields near the bottom of the convection zone. We have investigated to what extent the simulation results (obtained on the basis of the thin flux tube approximation) depend on the assumptions made about the initial state of a magnetic flux tube at the start of the simulation. Two initial conditions used in the literature have been considered in detail: mechanical equilibrium (MEQ) and temperature balance (TBL). It turns out that the requirement of super-equipartition field strength is a robust feature of the simulations, largely independent of the choice of initial conditions: emergence of active regions at low latitudes and the correct dependence of their tilt angle (with respect to the east-west direction) as a function of heliographic latitude require an initial magnetic field strength on the order of 105 G. Other properties of rising flux tubes, such as the asymmetries of shape and field strength between the leading and following wings (with respect to the direction of rotation) of a rising loop, or the anchoring of part of the flux tube in the overshoot region, depend on the initial condition. Observed asymmetries in the magnetic flux distribution and of proper motions in emerging active regions favor MEQ over TBL as the proper initial condition. MEQ should also be preferred for other theoretical reasons: it allows for fewer free parameters, it requires no fine tuning for the tube geometry and background stratification in the overshoot region, and it can be easily made compatible with an encompassing model of the generation, storage, and eruption of the magnetic flux. We have also studied whether an external upflow (convective updraft) can trigger the eruption of an otherwise stably stored flux tube in the overshoot region. We find that a significant deformation and destabilization of a flux tube with equipartition field strength requires coherent upflow velocities of 20-50 m s-1 in the overshoot layer, which is an order of magnitude larger than current estimates for such velocities. Title: Predicted Starspot Distributions on Pre-MS Stars Authors: Granzer, Th.; Strassmeier, K. G.; Schussler, M.; Caligari, P. Bibcode: 1998ASPC..154.1977G Altcode: 1998csss...10.1977G We present an application of the magnetic flux-tube model of Caligari (1995, 1991) to pre-main-sequence stars. This model was originally designed as an explanation for sunspots. The primary goal is to derive the emerging latitude of flux tubes for a large parameter volume including stellar mass, age, and rotational period. Since the original model worked well in explaining certain sunspot features, the next step would be to compare our model predictions with observed starspot distributions obtained by Doppler imaging techniques. Title: Origin of the Proper Motions of Emerging Bipolar Magnetic Regions Authors: Caligari, P.; Schussler, M.; Moreno-Insertis, F. Bibcode: 1997ASPC..118...76C Altcode: 1997fasp.conf...76C We have performed numerical simulations of the rise of magnetic flux tubes through the convection zone. We find that the observed proper motions of pores and sunspots in young active regions can be understood as a consequence of the Coriolis force: conservation of angular momentum leads to a retardation of the rising flux loop with respect to those parts of the flux tube that remain anchored in the overshoot layer below the convection zone proper. The result is an asymmetric shape with the following flank of the loop being more vertical than the leading part. When emerging at the solar surface, the asymmetric shape of the tube leads to proper motions which are in qualitative agreement with the observations. By studying the dependence of the asymmetry on the initial state of the flux tube we find that the observed proper motions favor a mechanical equilibrium of the magnetic field in the overshoot layer. We also find that small active regions (emerging from flux tubes with little magnetic flux) are less asymmetric and should show weaker proper motions than large bipolar regions. This prediction can be put to an observational test. Title: Distribution of starspots on cool stars. I. Young and main sequence stars of 1Msun_. Authors: Schuessler, M.; Caligari, P.; Ferriz-Mas, A.; Solanki, S. K.; Stix, M. Bibcode: 1996A&A...314..503S Altcode: Sunspots are restricted to a latitude band within 30degof the solar equator. In contrast, the latitudes of spots on the surfaces of rapidly rotating cool stars can range from their polar regions, for RS CVn systems and for T Tauri stars leaving the Hayashi track, to mid latitudes for stars close to or on the main sequence. In order to find an explanation for these observed spot latitudes we have applied the criteria for the undulatory instability (Parker instability) of a toroidal magnetic flux tube embedded in the convective overshoot layer below the outer convection zone and calculated the non-linear evolution of the rising magnetic loops formed by this instability. We describe the results for a star of one solar mass in different phases of its evolution before and on the main sequence. We find that there usually is a range of latitudes at which magnetic flux can emerge on the stellar surface. The mean latitude of emergence shifts towards the poles for increasingly rapid rotation. The internal structure of the star, however, plays an almost equally important role in determining the latitude of magnetic emergence. For stars of solar mass only the youngest objects, with extremely deep convection zones, should show spots emerging at the stellar poles. Pre-main sequence stars at an age of 10^7^ y (convection zone reaching down half-way to the centre) exhibit high latitude, but not truly polar spots, while a main sequence star of one solar mass, even at high rotation rates, only shows intermediate latitude spots. These results are found to be in good agreement with Doppler images of young rapid rotators. Title: Flux Tube Dynamics in Active Stars Authors: Caligari, P.; Schüssler, M.; Solanki, S. K.; Schaerer, D.; Stix, M. Bibcode: 1996ApL&C..34...17C Altcode: No abstract at ADS Title: ``Explosion'' and Intensification of Magnetic Flux Tubes Authors: Moreno-Insertis, F.; Caligari, P.; Schuessler, M. Bibcode: 1995ApJ...452..894M Altcode: A magnetic flux tube anchored at the bottom of the solar convection zone and rising toward the surface as a result of an undulatory instability can be affected by a sudden catastrophic expansion and weakening of the magnetic field at its apex if the original field strength is below a few times 104 G. Such an "explosion" occurs if the flux tube evolves close enough to (adiabatic) hydrostatic equilibrium along the magnetic field lines in a super-adiabatically stratified environment. This condition is satisfied if the diameter of the tube is small enough for the drag force to dominate the dynamical evolution. For example, rising flux tubes with equipartition field (104 G) at their basis explode in the middle of the convection zone if their magnetic flux is below ≌1021 Mx.

Apart from preventing flux tubes with equipartition field from reaching the surface, the explosion process may have other consequences for the evolution of magnetic fields in the convection zone: (a) it provides a source of weak field to be acted upon by the convective flows in the course of a turbulent dynamo process; (b) upflow of matter into the inflated top of a loop intensifies the magnetic field in the submerged part of the flux tube at the bottom of the convection zone. This might constitute a mechanism to produce the strong azimuthal fields in the overshoot region suggested by recent studies of the undular instability of magnetic flux tubes. Title: Emerging Flux Tubes in the Solar Convection Zone. I. Asymmetry, Tilt, and Emergence Latitude Authors: Caligari, P.; Moreno-Insertis, F.; Schussler, M. Bibcode: 1995ApJ...441..886C Altcode: The process of emergence of magnetic flux from the depths of the convection zone to the surface is presented in the framework of self-consistent model for the storage of field in the lower overshoot regions and as the mechanism responsible for some of the regularities observed in active regions. We have performed numerical simulations of the emergence of flux tubes in the solar convection zone including the effects of spherical geometry and rotation. The magnetic flux tubes can be stored in mechanical equilibrium in the overshoot region, which is the natural equilibrium of the flux rings in a subadiabatic layer. An undular instability leads to the formation of loops once a critical magnetic field strength of the order of 105 G is exceeded. In the nonlinear phase of their unstable evolution, the tubes move across the convection zone on a very fast time-scale, typically about one month. The geometry and dynamics of the flux tubes studied in these simulations permit prediction of some of the observed properties of the active regions. First, the wings of the tube show a marked asymmetry of inclination and velocity, which is compatible with the observed asymmetric proper motions of sunspots and with the position of the neutral line in emerging active regions. Second, upon emergence the flux tubes show a tilt angle with respect to the equator which fits reasonably well with the observed values. Third, the flux tubes rise roughly within a cone of radial directions in the Sun so that no outbreak at high latitudes takes place. The calculations lend further support to the possibility of superequipartition field strengths in the overshoot region. The implications of the present results for the dynamo mechanism are discussed and hints for observational work are also given. Title: Observation of Surface Activity on Cool Giants with the VLT Interferometer Authors: von der Lühe, O.; Schüssler, M.; Solanki, S. K.; Caligari, P. Bibcode: 1995svlt.conf...94V Altcode: No abstract at ADS Title: Active Region Asymmetry as a Result of the Rise of Magnetic Flux Tubes Authors: Moreno-Insertis, F.; Caligari, P.; Schuessler, M. Bibcode: 1994SoPh..153..449M Altcode: The magnetic flux tubes that rise across the convection zone to produce active regions are shown to develop a difference in inclination between their preceding and follower sides. This asymmetry is such that the follower wing is more vertical (i.e., closer to the radial direction) than the preceding side. An asymmetry of this kind can be obtained as a natural consequence of the conservation of angular momentum along the rise. This process may explain a number of the observed asymmetries in morphology and behavior of the preceding and follower parts of the active regions. We present results of numerical simulations showing this effect and discuss possible observational consequences. Title: Distribution of Magnetic Flux on the Surface of Rapidly Rotating Stars Authors: Caligari, P.; Schussler, M.; Stix, M.; Solanki, S. K. Bibcode: 1994ASPC...64..387C Altcode: 1994csss....8..387C No abstract at ADS Title: Dynamics of erupting magnetic flux tubes Authors: Moreno-Insertis, F.; Schüssler, M.; Caligari, P. Bibcode: 1994ASIC..433..407M Altcode: 1994ssm..work..407M The eruption of magnetic flux tubes from the overshoot layer due to instability and the dynamics of their subsequent rise through the solar convection zone are followed by numerical simulation. Special emphasis is put on the possibility of explaining observed regularities of the active regions at the surface (tilt angles, latitude of emergence, asymmetry between preceding and following parts, etc). Instability sets in with non-axisymmetric (undular) modes at azimuthal wavenumbers $m=1$ and $m=2$ if the field strength exceeds values of the order of $10^5$ G. At the same time, such strong initial fields are required to reproduce the observable properties of sunspots and active regions. Consequently, a consistent picture of storage, instability and eruption of solar magnetic fields emerges. Title: Instability and eruption of magnetic flux tubes Authors: Caligari, P.; Ferriz-Mas, A.; Moreno-Insertis, F.; Schüssler, M. Bibcode: 1994smf..conf..139C Altcode: No abstract at ADS Title: Flux tube dynamics in pre-main-sequence and giant stars. Authors: Caligari, P.; Schaerer, D.; Schüssler, M.; Solanki, S. Bibcode: 1994AGAb...10...92C Altcode: No abstract at ADS Title: Instability and eruption of magnetic flux tubes in the solar convection zone. Authors: Schussler, M.; Caligari, P.; Ferriz-Mas, A.; Moreno-Insertis, F. Bibcode: 1994A&A...281L..69S Altcode: We present a consistent model of storage, instability and dynamical eruption of magnetic flux tubes in the solar convection zone and underlying overshoot region. Using a convection zone model with self-consistent overshoot layer, we calculate equilibrium configurations of magnetic flux tubes and determine their linear stability properties, taking into consideration the effects of stratification and rotation. Instability of flux tubes stored in the overshoot layer with growth times below one year requires field strengths of the order of 105 G; in many cases, the dominant mode has an azimuthal wave number of m = 2. Numerical simulations are used to follow the nonlinear evolution of such unstable flux tubes and their rise through the convection zone, from which they emerge to form active regions. The results are in accordance with the following two requirements, based on observational facts: (a) the upward motion of the tubes is not significantly deflected by the Coriolis force so that they can emerge at low latitudes, (b) their inclination with respect to the East-West direction (tilt angle) as a function of the latitude of emergence is consistent with observations of acitve regions. Title: Instability of magnetic flux tubes in the solar convection zone. Authors: Caligari, P.; Moreno-Insertis, F.; Schüssler, M. Bibcode: 1992AGAb....7..152C Altcode: No abstract at ADS