Guus Sliepen - Academia.edu (original) (raw)

Papers by Guus Sliepen

Research paper thumbnail of <title>Mechanical design of a completely open-foldable dome for EST</title>

Ground-based and Airborne Telescopes III, 2010

In the context of the EST design study for a 4m-class solar telescope and a study for large open-... more In the context of the EST design study for a 4m-class solar telescope and a study for large open-foldable domes of the Dutch Technology Foundation STW, a design is made for the 20 to 30m diameter range. Detailed designs are made for three specific diameter sizes: 23, 28 and 33m. Smaller-size open-foldable domes based on tensioned cloth and in use at the Dutch Open Telescope (7m) and the GREGOR (9m) have proven to be all-weather stable and very effective for good seeing conditions for solar telescopes. The cloth has shown no degradation over the past 14 (DOT) resp. 6 (GREGOR) years of experience and no permanent elongation with the frequent de-tensioning and tensioning during opening and closing. The application of cloth permits a dome design leaving, when opened, the telescope completely free without any structure over the telescope and no massive structures besides or under it. Basis for the new design is the available prestretched stable cloth, which is nowadays produced in much stronger qualities than used for DOT and GREGOR. The larger curvature radius requires larger tension in the cloth, but combination with stronger cloth fits for the upscaling. Calculations show that the steel construction geometries of the GREGOR dome can be upscaled with a few adjustments. Bearings and drives remain within normal sizes. Cost calculations show that open-foldable domes of this size are remarkably lower in price than closed domes. In addition, an interesting option is presented for a semi-transparent windshield of which the position can be adapted to the wind direction. This shield gives an effective wind protection of the region around the primary mirror without disturbing the wind flows above the shield and without stagnant air or big eddies behind it. It is storm safe and the costs are only a fraction of the open-foldable dome costs.

Research paper thumbnail of <title>Tunable H-alpha Lyot filter with advanced servo system and image processing: instrument design and new scientific results with the Dutch Open Telescope</title>

Ground-based and Airborne Instrumentation for Astronomy, 2006

The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma is a revolutionary open solar ... more The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma is a revolutionary open solar telescope, on an excellent site, on top of a transparent tower of steel framework, and uses natural air flow to minimize local seeing. The DOT is a high-resolution multi-wavelength imager capable of long-duration time series aiming at magnetic fine structure, topology and dynamics in the photosphere and low-and high chromosphere. In this paper we describe the latest addition to the multi-wavelength imaging system: a Lyot H-alpha camera channel operating at a wavelength of 656.3 nm, being of major interest for high-chromospheric phenomena. The channel is operated strictly synchronous with the other channels and all data are speckle reconstructed. The channel permits profile sampling and delivers Dopplergrams in a 15 second time cadence, up to several hours long and adding up to a total data amount of 1.6 Terabyte/day. A dedicated computer (DSP, DOT Speckle Processor) has been built for processing the data overnight.

Research paper thumbnail of <title>The Irkutsk Barium filter for narrow-band wide-field high-resolution solar images at the Dutch Open Telescope</title>

Ground-based and Airborne Instrumentation for Astronomy III, 2010

A wide-field birefringent filter for the barium II line at 455.4nm is developed in Irkutsk. The B... more A wide-field birefringent filter for the barium II line at 455.4nm is developed in Irkutsk. The Barium line is excellent for Doppler-shift measurements because of low thermal line-broadening and steep flanks of the line profile. The filter width is 0.008nm and the filter is tunable over 0.4nm through the whole line and far enough in the neighboring regions. A fast tuning system with servomotor is developed at the Dutch Open Telescope (DOT). Observations are done in speckle mode with 10 images per second and Keller-VonDerLühe reconstruction using synchronous images of a nearby bluecontinuum channel at 450.5nm. Simultaneous observation of several line positions, typically 3 or 5, are made with this combination of fast tuning and speckle. All polarizers are birefringent prisms which largely reduced the light loss compared to polarizing sheets. The advantage of this filter over Fabry-Perot filters is its wide field due to a large permitted entrance angle and no need of polishing extremely precise surfaces. The BaII observations at the DOT occur simultaneously with those of a fast-tunable birefringent H-alpha filter. This gives the unique possibility of simultaneous speckle-reconstructed observations of velocities in photosphere (BaII) and chromosphere (H-alpha).

Research paper thumbnail of <title>Cornelis Zwaan, open principle, and the future of high-resolution solar telescopes</title>

Ground-based and Airborne Telescopes II, 2008

It was in the years around 1970 that during site-test campaigns for JOSO masts were erected up ti... more It was in the years around 1970 that during site-test campaigns for JOSO masts were erected up till 30 m height with sensors at several heights for the measurement of temperature fluctuations. Cornelis (Kees) Zwaan discovered that the fluctuations decrease drastically at heights from about 15 m and upward when there is some wind. The conclusion from this experience was the open telescope principle: the telescope should be completely free in the air 15 m or more above the ground. The Dutch Open Telescope (DOT) was the pioneering demonstrator of the open-telescope technology. Now that larger high-resolution telescopes come in view, it is time to analyze again the principle: (i) the essentials for proper working of the open principle; (ii) the differences with nighttime observations particularly concerning the seeing; (iii) the design consequences for the new generation of high-resolution solar telescopes.

Research paper thumbnail of <title>Large fully retractable telescope enclosures still closable in strong wind</title>

Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, 2008

Two prototypes of fully retractable enclosures with diameters of 7 and 9 m have been built for th... more Two prototypes of fully retractable enclosures with diameters of 7 and 9 m have been built for the high-resolution solar telescopes DOT (Dutch Open Telescope) and GREGOR, both located at the Canary Islands. These enclosures protect the instruments for bad weather and are fully open when the telescopes are in operation. The telescopes and enclosures also operate in hard wind. The prototypes are based on tensioned membrane between movable but stiff bows, which fold together to a ring when opened. The height of the ring is small. The prototypes already survived several storms, with often snow and ice, without any damage, including hurricane Delta with wind speeds up to 68 m/s. The enclosures can still be closed and opened with wind speeds of 20 m/s without any problems or restrictions. The DOT successfully demonstrated the open, wind-flushing concept for astronomical telescopes. It is now widely recognized that also large future telescopes benefit from wind-flushing and retractable enclosures. These telescopes require enclosures with diameters of 30 m until roughly 100 m, the largest sizes for the ELTs (Extreme Large Telescopes), which will be built in the near future. We discuss developments and required technology for the realization of these large sizes.

Research paper thumbnail of <title>Fast foldable tent domes</title>

Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, 2008

In the near future ELTs (Extreme Large Telescopes) will be built. Preferably these telescopes sho... more In the near future ELTs (Extreme Large Telescopes) will be built. Preferably these telescopes should operate without obstructions in the near surrounding to reach optimal seeing conditions and avoid large turbulences with wind-gust accelerations around large obstacles. This applies also to future large solar telescopes. At present two foldable dome prototypes have been built on the Canary Islands: the Dutch Open Telescope (DOT, La Palma) and the GREGOR Telescope (Tenerife), having a diameter of 7 and 9 meter, respectively. The domes are usually fully retracted during observations. The research consists of measurements on the two domes. New camera systems are developed and placed inside the domes for precise dome deformation measurements within 0.1 mm over the whole dome size. Simultaneously, a variety of wind-speed and -direction sensors measure the wind field around the dome. In addition, fast sensitive airpressure sensors placed on the supporting bows measure the wind pressure. The aim is to predict accurately the expected forces and deformations on up-scaled, fully retractable domes to make their construction more economically. The dimensions of 7 and 9 meter are large enough for realistic on-site tests in gusty wind and will give much more information than wind tunnel experiments.

Research paper thumbnail of <title>Contactless sub-millimeter displacement measurements</title>

Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, 2008

Weather effects on foldable domes, as used at the DOT and GREGOR, are investigated, in particular... more Weather effects on foldable domes, as used at the DOT and GREGOR, are investigated, in particular the correlation between the wind field and the stresses caused to both metal framework and tent clothing. Camera systems measure contactless the displacement of several dome points. The stresses follow from the measured deformation pattern. The cameras placed near the dome floor do not disturb telescope operations. In the set-ups of DOT and GREGOR, these cameras are up to 8 meters away from the measured points and must be able to detect displacements of less than 0.1 mm. The cameras have a FireWire (IEEE1394) interface to eliminate the need for frame grabbers. Each camera captures 15 images of 640 × 480 pixels per second. All data is processed on-site in real-time. In order to get the best estimate for the displacement within the constraints of available processing power, all image processing is done in Fourier-space, with all convolution operations being pre-computed once. A sub-pixel estimate of the peak of the correlation function is made. This enables to process the images of four cameras using only one commodity PC with a dual-core processor, and achieve an effective sensitivity of up to 0.01 mm. The deformation measurements are well correlated to the simultaneous wind measurements. The results are of high interest to upscaling the dome design (ELTs and solar telescopes).

Research paper thumbnail of Large-field high-resolution mosaic movies

Ground-based and Airborne Telescopes IV, 2012

Research paper thumbnail of <title>Seeing measurements with autonomous, short-baseline shadow band rangers</title>

Ground-based and Airborne Telescopes III, 2010

There is growing interest in measuring seeing at existing and prospective telescope sites. Severa... more There is growing interest in measuring seeing at existing and prospective telescope sites. Several methods exist to quantify seeing, one among them is by measuring the scintillation of solar or lunar light using a photodiode. A shadow band ranger (SHABAR) analyses the covariance of the signals from an array of such photodiodes, which allows for the spatial resolution of the index of refraction above the SHABAR device. This allows one to estimate the index of refraction structure parameter as a function of height, C 2 n (h). Although a SHABAR has a limited range compared to a differential image motion monitor (DIMM) or the latest wavefront sensors, the advantage is that it does not need telescope optics to work. A SHABAR device can be made very compact and can operate independent of other instruments. We describe the design of such a SHABAR device with six photodiodes that can operate virtually indefinitely without requiring human intervention.

Research paper thumbnail of <title>Foldable dome climate measurements and thermal properties</title>

Ground-based and Airborne Telescopes III, 2010

As part of a larger project for measuring various aspects of foldable domes in the context of EST... more As part of a larger project for measuring various aspects of foldable domes in the context of EST and with support of the Dutch Technology Foundation STW, we have collected over a year of continuous temperature and humidity measurements, both inside and outside the domes of the Dutch Open Telescope (DOT) on La Palma 5 and the GREGOR telescope on Tenerife. 6 In addition, we have measured the wind field around each dome.

Research paper thumbnail of The GREGOR dome, pathfinder for the EST dome

Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 2012

ABSTRACT The completely open-foldable dome of the GREGOR telescope is a further development of th... more ABSTRACT The completely open-foldable dome of the GREGOR telescope is a further development of the DOT dome, respectively 9 and 7 meter in diameter. New technical developments are implemented and tested at the GREGOR dome, that are important for the design of the much larger dome for the EST, which will be 28 meter in diameter. The GREGOR dome is the first with more than one clamp working simultaneously for closing the dome and bringing the membranes on the required high tension for storm resistance. The storm Delta with 245 km/h 1-minute mean maximum at the location of the GREGOR gave no problems nor did the storms afterwards. Opening and closing experiences are up to wind speeds of 90 km/h without problems. Good observing circumstances never occur with higher wind speeds. A double layer of membranes is applied in the GREGOR construction whereas the DOT dome is equipped with a single layer. Simultaneous climate measurements inside and outside the dome have proven the thermal-insulation capability of this double-layer construction. The experiences with the GREGOR showed that the elongation by tensioning of the prestrained membrane material is much lower than originally expected. In the meantime, more strong and stiff membrane material is available and applied in the EST design. As a consequence, the clamps of the EST can have a relatively much shorter length and there is no need anymore for simultaneous operation of the clamps and the main actuators in low speed with help of a frequency inverter. The clamps can close after the main bow operation is finished, which simplifies the electrical control.

Research paper thumbnail of The enclosure for the European Solar Telescope (EST)

Ground-Based and Airborne Telescopes Iii, 2010

The European Solar Telescope (EST) is a 4-m class solar telescope, which is currently in the conc... more The European Solar Telescope (EST) is a 4-m class solar telescope, which is currently in the conceptual design phase. EST will be located in the Canary Islands and aims at observations with high spectral, spatial and temporal resolution of the solar photosphere and chromosphere.

Research paper thumbnail of Large-field high-resolution mosaic movies

Optical Engineering, 2013

Movies with fields-of-view larger than normal, for high-resolution telescopes, will give a better... more Movies with fields-of-view larger than normal, for high-resolution telescopes, will give a better understanding of processes on the Sun such as filament and active region developments and their possible interactions. New active regions can serve as an igniter of the eruption of a nearby filament. A method to create a large field-of-view is to join several fields-of-view into a mosaic. Fields are imaged quickly, one after another, using fast telescope-pointing. Such a pointing cycle has been automated at the Dutch open telescope (DOT), a high-resolution solar telescope located on the Canary Island La Palma. The number and positions of the subfields are calculated automatically and represented by an array of bright points in the guider image which indicates the subfield centers inside the drawn rectangle of the total field on the computer screen with the whole-sun image. Automatic production of flats is also programmed. For the first time, mosaic movies were programmed from stored information on automated telescope motions. The mosaic movies show larger regions of the solar disk in high resolution and fill a gap between available whole-sun images with limited spatial resolution of synoptic telescopes including space instruments and small-field high-cadence movies of high-resolution solar telescopes. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Research paper thumbnail of Open Principle for Large High-Resolution Solar Telescopes

Earth, Moon, and Planets, 2009

Vacuum solar telescopes solve the problem of image deterioration inside the telescope due to refr... more Vacuum solar telescopes solve the problem of image deterioration inside the telescope due to refractive index fluctuations of the air heated by the solar light. However, such telescopes have a practical diameter limit somewhat over 1 m. The Dutch Open Telescope (DOT) was the pioneering demonstrator of the open-telescope technology without need of vacuum, now pursued in the German GREGOR. Important ingredients for this technology are primary beam completely open to natural wind flow, stiff but still open design by principal stiff overall geometries in combination with carefully designed joints and completely open-foldable dome constructions based on tensioned strong cloth. Further developments to large sizes are made within the framework of the design study for a European Solar Telescope (EST).

Research paper thumbnail of <title>Data handling and control for the European Solar Telescope</title>

Software and Cyberinfrastructure for Astronomy, 2010

We introduce the concepts for the control and data handling systems of the European Solar Telesco... more We introduce the concepts for the control and data handling systems of the European Solar Telescope (EST), the main functional and technical requirements for the definition of these systems, and the outcomes from the trade-off analysis to date. Concerning the telescope control, EST will have performance requirements similar to those of current medium-sized night-time telescopes. On the other hand, the science goals of EST require the simultaneous operation of three instruments and of a large number of detectors. This leads to a projected data flux that will be technologically challenging and exceeds that of most other astronomical projects. We give an overview of the reference design of the control and data handling systems for the EST to date, focusing on the more critical and innovative aspects resulting from the overall design of the telescope. Downloaded from SPIE Digital Library on 04 Oct 2010 to 161.72.52.8. Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 7740 77400G-2 Downloaded from SPIE Digital Library on 04 Oct 2010 to 161.72.52.8. Terms of Use: http://spiedl.org/terms

Research paper thumbnail of <title>Mechanical design of a completely open-foldable dome for EST</title>

Ground-based and Airborne Telescopes III, 2010

In the context of the EST design study for a 4m-class solar telescope and a study for large open-... more In the context of the EST design study for a 4m-class solar telescope and a study for large open-foldable domes of the Dutch Technology Foundation STW, a design is made for the 20 to 30m diameter range. Detailed designs are made for three specific diameter sizes: 23, 28 and 33m. Smaller-size open-foldable domes based on tensioned cloth and in use at the Dutch Open Telescope (7m) and the GREGOR (9m) have proven to be all-weather stable and very effective for good seeing conditions for solar telescopes. The cloth has shown no degradation over the past 14 (DOT) resp. 6 (GREGOR) years of experience and no permanent elongation with the frequent de-tensioning and tensioning during opening and closing. The application of cloth permits a dome design leaving, when opened, the telescope completely free without any structure over the telescope and no massive structures besides or under it. Basis for the new design is the available prestretched stable cloth, which is nowadays produced in much stronger qualities than used for DOT and GREGOR. The larger curvature radius requires larger tension in the cloth, but combination with stronger cloth fits for the upscaling. Calculations show that the steel construction geometries of the GREGOR dome can be upscaled with a few adjustments. Bearings and drives remain within normal sizes. Cost calculations show that open-foldable domes of this size are remarkably lower in price than closed domes. In addition, an interesting option is presented for a semi-transparent windshield of which the position can be adapted to the wind direction. This shield gives an effective wind protection of the region around the primary mirror without disturbing the wind flows above the shield and without stagnant air or big eddies behind it. It is storm safe and the costs are only a fraction of the open-foldable dome costs.

Research paper thumbnail of <title>Tunable H-alpha Lyot filter with advanced servo system and image processing: instrument design and new scientific results with the Dutch Open Telescope</title>

Ground-based and Airborne Instrumentation for Astronomy, 2006

The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma is a revolutionary open solar ... more The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma is a revolutionary open solar telescope, on an excellent site, on top of a transparent tower of steel framework, and uses natural air flow to minimize local seeing. The DOT is a high-resolution multi-wavelength imager capable of long-duration time series aiming at magnetic fine structure, topology and dynamics in the photosphere and low-and high chromosphere. In this paper we describe the latest addition to the multi-wavelength imaging system: a Lyot H-alpha camera channel operating at a wavelength of 656.3 nm, being of major interest for high-chromospheric phenomena. The channel is operated strictly synchronous with the other channels and all data are speckle reconstructed. The channel permits profile sampling and delivers Dopplergrams in a 15 second time cadence, up to several hours long and adding up to a total data amount of 1.6 Terabyte/day. A dedicated computer (DSP, DOT Speckle Processor) has been built for processing the data overnight.

Research paper thumbnail of <title>The Irkutsk Barium filter for narrow-band wide-field high-resolution solar images at the Dutch Open Telescope</title>

Ground-based and Airborne Instrumentation for Astronomy III, 2010

A wide-field birefringent filter for the barium II line at 455.4nm is developed in Irkutsk. The B... more A wide-field birefringent filter for the barium II line at 455.4nm is developed in Irkutsk. The Barium line is excellent for Doppler-shift measurements because of low thermal line-broadening and steep flanks of the line profile. The filter width is 0.008nm and the filter is tunable over 0.4nm through the whole line and far enough in the neighboring regions. A fast tuning system with servomotor is developed at the Dutch Open Telescope (DOT). Observations are done in speckle mode with 10 images per second and Keller-VonDerLühe reconstruction using synchronous images of a nearby bluecontinuum channel at 450.5nm. Simultaneous observation of several line positions, typically 3 or 5, are made with this combination of fast tuning and speckle. All polarizers are birefringent prisms which largely reduced the light loss compared to polarizing sheets. The advantage of this filter over Fabry-Perot filters is its wide field due to a large permitted entrance angle and no need of polishing extremely precise surfaces. The BaII observations at the DOT occur simultaneously with those of a fast-tunable birefringent H-alpha filter. This gives the unique possibility of simultaneous speckle-reconstructed observations of velocities in photosphere (BaII) and chromosphere (H-alpha).

Research paper thumbnail of <title>Cornelis Zwaan, open principle, and the future of high-resolution solar telescopes</title>

Ground-based and Airborne Telescopes II, 2008

It was in the years around 1970 that during site-test campaigns for JOSO masts were erected up ti... more It was in the years around 1970 that during site-test campaigns for JOSO masts were erected up till 30 m height with sensors at several heights for the measurement of temperature fluctuations. Cornelis (Kees) Zwaan discovered that the fluctuations decrease drastically at heights from about 15 m and upward when there is some wind. The conclusion from this experience was the open telescope principle: the telescope should be completely free in the air 15 m or more above the ground. The Dutch Open Telescope (DOT) was the pioneering demonstrator of the open-telescope technology. Now that larger high-resolution telescopes come in view, it is time to analyze again the principle: (i) the essentials for proper working of the open principle; (ii) the differences with nighttime observations particularly concerning the seeing; (iii) the design consequences for the new generation of high-resolution solar telescopes.

Research paper thumbnail of <title>Large fully retractable telescope enclosures still closable in strong wind</title>

Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, 2008

Two prototypes of fully retractable enclosures with diameters of 7 and 9 m have been built for th... more Two prototypes of fully retractable enclosures with diameters of 7 and 9 m have been built for the high-resolution solar telescopes DOT (Dutch Open Telescope) and GREGOR, both located at the Canary Islands. These enclosures protect the instruments for bad weather and are fully open when the telescopes are in operation. The telescopes and enclosures also operate in hard wind. The prototypes are based on tensioned membrane between movable but stiff bows, which fold together to a ring when opened. The height of the ring is small. The prototypes already survived several storms, with often snow and ice, without any damage, including hurricane Delta with wind speeds up to 68 m/s. The enclosures can still be closed and opened with wind speeds of 20 m/s without any problems or restrictions. The DOT successfully demonstrated the open, wind-flushing concept for astronomical telescopes. It is now widely recognized that also large future telescopes benefit from wind-flushing and retractable enclosures. These telescopes require enclosures with diameters of 30 m until roughly 100 m, the largest sizes for the ELTs (Extreme Large Telescopes), which will be built in the near future. We discuss developments and required technology for the realization of these large sizes.

Research paper thumbnail of <title>Fast foldable tent domes</title>

Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, 2008

In the near future ELTs (Extreme Large Telescopes) will be built. Preferably these telescopes sho... more In the near future ELTs (Extreme Large Telescopes) will be built. Preferably these telescopes should operate without obstructions in the near surrounding to reach optimal seeing conditions and avoid large turbulences with wind-gust accelerations around large obstacles. This applies also to future large solar telescopes. At present two foldable dome prototypes have been built on the Canary Islands: the Dutch Open Telescope (DOT, La Palma) and the GREGOR Telescope (Tenerife), having a diameter of 7 and 9 meter, respectively. The domes are usually fully retracted during observations. The research consists of measurements on the two domes. New camera systems are developed and placed inside the domes for precise dome deformation measurements within 0.1 mm over the whole dome size. Simultaneously, a variety of wind-speed and -direction sensors measure the wind field around the dome. In addition, fast sensitive airpressure sensors placed on the supporting bows measure the wind pressure. The aim is to predict accurately the expected forces and deformations on up-scaled, fully retractable domes to make their construction more economically. The dimensions of 7 and 9 meter are large enough for realistic on-site tests in gusty wind and will give much more information than wind tunnel experiments.

Research paper thumbnail of <title>Contactless sub-millimeter displacement measurements</title>

Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, 2008

Weather effects on foldable domes, as used at the DOT and GREGOR, are investigated, in particular... more Weather effects on foldable domes, as used at the DOT and GREGOR, are investigated, in particular the correlation between the wind field and the stresses caused to both metal framework and tent clothing. Camera systems measure contactless the displacement of several dome points. The stresses follow from the measured deformation pattern. The cameras placed near the dome floor do not disturb telescope operations. In the set-ups of DOT and GREGOR, these cameras are up to 8 meters away from the measured points and must be able to detect displacements of less than 0.1 mm. The cameras have a FireWire (IEEE1394) interface to eliminate the need for frame grabbers. Each camera captures 15 images of 640 × 480 pixels per second. All data is processed on-site in real-time. In order to get the best estimate for the displacement within the constraints of available processing power, all image processing is done in Fourier-space, with all convolution operations being pre-computed once. A sub-pixel estimate of the peak of the correlation function is made. This enables to process the images of four cameras using only one commodity PC with a dual-core processor, and achieve an effective sensitivity of up to 0.01 mm. The deformation measurements are well correlated to the simultaneous wind measurements. The results are of high interest to upscaling the dome design (ELTs and solar telescopes).

Research paper thumbnail of Large-field high-resolution mosaic movies

Ground-based and Airborne Telescopes IV, 2012

Research paper thumbnail of <title>Seeing measurements with autonomous, short-baseline shadow band rangers</title>

Ground-based and Airborne Telescopes III, 2010

There is growing interest in measuring seeing at existing and prospective telescope sites. Severa... more There is growing interest in measuring seeing at existing and prospective telescope sites. Several methods exist to quantify seeing, one among them is by measuring the scintillation of solar or lunar light using a photodiode. A shadow band ranger (SHABAR) analyses the covariance of the signals from an array of such photodiodes, which allows for the spatial resolution of the index of refraction above the SHABAR device. This allows one to estimate the index of refraction structure parameter as a function of height, C 2 n (h). Although a SHABAR has a limited range compared to a differential image motion monitor (DIMM) or the latest wavefront sensors, the advantage is that it does not need telescope optics to work. A SHABAR device can be made very compact and can operate independent of other instruments. We describe the design of such a SHABAR device with six photodiodes that can operate virtually indefinitely without requiring human intervention.

Research paper thumbnail of <title>Foldable dome climate measurements and thermal properties</title>

Ground-based and Airborne Telescopes III, 2010

As part of a larger project for measuring various aspects of foldable domes in the context of EST... more As part of a larger project for measuring various aspects of foldable domes in the context of EST and with support of the Dutch Technology Foundation STW, we have collected over a year of continuous temperature and humidity measurements, both inside and outside the domes of the Dutch Open Telescope (DOT) on La Palma 5 and the GREGOR telescope on Tenerife. 6 In addition, we have measured the wind field around each dome.

Research paper thumbnail of The GREGOR dome, pathfinder for the EST dome

Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 2012

ABSTRACT The completely open-foldable dome of the GREGOR telescope is a further development of th... more ABSTRACT The completely open-foldable dome of the GREGOR telescope is a further development of the DOT dome, respectively 9 and 7 meter in diameter. New technical developments are implemented and tested at the GREGOR dome, that are important for the design of the much larger dome for the EST, which will be 28 meter in diameter. The GREGOR dome is the first with more than one clamp working simultaneously for closing the dome and bringing the membranes on the required high tension for storm resistance. The storm Delta with 245 km/h 1-minute mean maximum at the location of the GREGOR gave no problems nor did the storms afterwards. Opening and closing experiences are up to wind speeds of 90 km/h without problems. Good observing circumstances never occur with higher wind speeds. A double layer of membranes is applied in the GREGOR construction whereas the DOT dome is equipped with a single layer. Simultaneous climate measurements inside and outside the dome have proven the thermal-insulation capability of this double-layer construction. The experiences with the GREGOR showed that the elongation by tensioning of the prestrained membrane material is much lower than originally expected. In the meantime, more strong and stiff membrane material is available and applied in the EST design. As a consequence, the clamps of the EST can have a relatively much shorter length and there is no need anymore for simultaneous operation of the clamps and the main actuators in low speed with help of a frequency inverter. The clamps can close after the main bow operation is finished, which simplifies the electrical control.

Research paper thumbnail of The enclosure for the European Solar Telescope (EST)

Ground-Based and Airborne Telescopes Iii, 2010

The European Solar Telescope (EST) is a 4-m class solar telescope, which is currently in the conc... more The European Solar Telescope (EST) is a 4-m class solar telescope, which is currently in the conceptual design phase. EST will be located in the Canary Islands and aims at observations with high spectral, spatial and temporal resolution of the solar photosphere and chromosphere.

Research paper thumbnail of Large-field high-resolution mosaic movies

Optical Engineering, 2013

Movies with fields-of-view larger than normal, for high-resolution telescopes, will give a better... more Movies with fields-of-view larger than normal, for high-resolution telescopes, will give a better understanding of processes on the Sun such as filament and active region developments and their possible interactions. New active regions can serve as an igniter of the eruption of a nearby filament. A method to create a large field-of-view is to join several fields-of-view into a mosaic. Fields are imaged quickly, one after another, using fast telescope-pointing. Such a pointing cycle has been automated at the Dutch open telescope (DOT), a high-resolution solar telescope located on the Canary Island La Palma. The number and positions of the subfields are calculated automatically and represented by an array of bright points in the guider image which indicates the subfield centers inside the drawn rectangle of the total field on the computer screen with the whole-sun image. Automatic production of flats is also programmed. For the first time, mosaic movies were programmed from stored information on automated telescope motions. The mosaic movies show larger regions of the solar disk in high resolution and fill a gap between available whole-sun images with limited spatial resolution of synoptic telescopes including space instruments and small-field high-cadence movies of high-resolution solar telescopes. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Research paper thumbnail of Open Principle for Large High-Resolution Solar Telescopes

Earth, Moon, and Planets, 2009

Vacuum solar telescopes solve the problem of image deterioration inside the telescope due to refr... more Vacuum solar telescopes solve the problem of image deterioration inside the telescope due to refractive index fluctuations of the air heated by the solar light. However, such telescopes have a practical diameter limit somewhat over 1 m. The Dutch Open Telescope (DOT) was the pioneering demonstrator of the open-telescope technology without need of vacuum, now pursued in the German GREGOR. Important ingredients for this technology are primary beam completely open to natural wind flow, stiff but still open design by principal stiff overall geometries in combination with carefully designed joints and completely open-foldable dome constructions based on tensioned strong cloth. Further developments to large sizes are made within the framework of the design study for a European Solar Telescope (EST).

Research paper thumbnail of <title>Data handling and control for the European Solar Telescope</title>

Software and Cyberinfrastructure for Astronomy, 2010

We introduce the concepts for the control and data handling systems of the European Solar Telesco... more We introduce the concepts for the control and data handling systems of the European Solar Telescope (EST), the main functional and technical requirements for the definition of these systems, and the outcomes from the trade-off analysis to date. Concerning the telescope control, EST will have performance requirements similar to those of current medium-sized night-time telescopes. On the other hand, the science goals of EST require the simultaneous operation of three instruments and of a large number of detectors. This leads to a projected data flux that will be technologically challenging and exceeds that of most other astronomical projects. We give an overview of the reference design of the control and data handling systems for the EST to date, focusing on the more critical and innovative aspects resulting from the overall design of the telescope. Downloaded from SPIE Digital Library on 04 Oct 2010 to 161.72.52.8. Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 7740 77400G-2 Downloaded from SPIE Digital Library on 04 Oct 2010 to 161.72.52.8. Terms of Use: http://spiedl.org/terms