Abstract. We derive formulae for all parameters dening the eld astigmatism of misaligned two mirr... more Abstract. We derive formulae for all parameters dening the eld astigmatism of misaligned two mirror telescopes with arbitrary geometries and with stop positions any-where on the line connecting the vertices of the two mir-rors. The formulae show explicitly the dependence of the eld astigmatism on the fundamental design parameters and characteristics of the telescope and on the stop posi-tion. Special attention is given to the particular case where such a schiefspiegler has been corrected for coma at the eld center. In addition, we study the eects of the prac-tical denition that the center of the eld is the center of the adapter. Following a recent paper by McLeod, where the eld dependence of astigmatism is used to collimate a Ritchey-Chretien telescope with the stop at the primary mirror, we apply our formulae to the Cassegrain focus of the ESO Very Large Telescope (VLT), where the stop is at the secondary mirror and the telescope is only corrected for spherical aberration. We prese...
Advanced Wavefront Control: Methods, Devices, and Applications III, 2005
The future European Extremely Large Telescope will be composed of one or two giant segmented mirr... more The future European Extremely Large Telescope will be composed of one or two giant segmented mirrors (up to 100 m of diameter) and of several large monolithic mirrors (up to 8 m in diameter). To limit the aberrations due to misalignments and defective surface quality it is necessary to have a proper active optics system. This active optics system must
The images at the f/35 Cassegrain focus of the 3.6-m telescope have never been excellent. As the ... more The images at the f/35 Cassegrain focus of the 3.6-m telescope have never been excellent. As the system (c.f. [1]) was initially installed and used to do only aperture photometry, this was never an issue of major concern. In fact, it could not even be measured directly. Only with the advent of mid-infrared cameras (here TIMMI [2],[3]) the image quality could be measured easily and systematically. Several reports state that the avEMMI is now working smoothly and reliably. Through a well-deserved recognition of his merits, Pierre has now been hired as staff astronomer at the CanadaFrance-Hawaii Telescope. I take advantage of this occasion to welcome the newcomers, and to wish success in their new activitities to those who have left us. Erratum
The Very Large Telescope (VLT) Observatory on Cerro Paranal (2635 m) in Northern Chile is approac... more The Very Large Telescope (VLT) Observatory on Cerro Paranal (2635 m) in Northern Chile is approaching completion. After the four 8-m Unit Telescopes (UT) individually saw first light in the last years, two of them were combined for the first time on October 30, 2001 to form a stellar interferometer, the VLT Interferometer. The remaining two UTs will be integrated into the interferometric array later this year. In this article, we will describe the subsystems of the VLTI and the planning for the following years.
The Prefocal Station (PFS) is the last opto-mechanical unit before the telescope focal plane in t... more The Prefocal Station (PFS) is the last opto-mechanical unit before the telescope focal plane in the Extremely Large Telescope (ELT) optical train. The PFS distributes the telescope optical beam to the Nasmyth and Coudé instrument focal stations and it contains all of the sky metrology (imaging and wavefront sensing) that will be used by the active optics of the telescope and to support operations such as phasing the primary mirror (phasing and diagnostic station). It also hosts local metrology that will be used for coarse alignment and maintenance. We present the main results of a concept design study for the Nasmyth A prefocal station.
The Giant Magellan Telescope (GMT)1 is a 25 m telescope composed of seven 8.4 m “unit telescopes”... more The Giant Magellan Telescope (GMT)1 is a 25 m telescope composed of seven 8.4 m “unit telescopes”, on a common mount. Each primary and conjugated secondary mirror segment will feed a common instrument interface, their focal planes co-aligned and co-phased. During telescope operation, the alignment of the optical components will deflect due to variations in thermal environment and gravity induced structural flexure of the mount. The ultimate co-alignment and co-phasing of the telescope is achieved by a combination of the Acquisition Guiding and Wavefront Sensing system and two segment edge-sensing systems2. An analysis of the capture range of the wavefront sensing system indicates that it is unlikely that that system will operate efficiently or reliably with initial mirror positions provided by open-loop corrections alone3. The project is developing a Telescope Metrology System (TMS) which incorporates a large number of absolute distance measuring interferometers. The system will align optical components of the telescope to the instrument interface to (well) within the capture range of the active optics wavefront sensing systems. The advantages offered by this technological approach to a TMS, over a network of laser trackers, are discussed. Initial investigations of the Etalon Absolute Multiline Technology™ by Etalon Ag4 show that a metrology network based on this product is capable of meeting requirements. A conceptual design of the system is presented and expected performance is discussed.
The concept of "Virtual Image Slicer" was developed and implemented at the Very Large T... more The concept of "Virtual Image Slicer" was developed and implemented at the Very Large Telescope (VLT). The Virtual Image Slicer consists in elongating the stars in a given direction by the use of the Active Optics of the telescope. Alignment of the major axis of the elongated star along the entrance slit of the spectrograph allows to increase the total signal collected in a single (polarimetric) spectrum by a factor of up to 100 or more relative to a perfectly shaped image for bright sources.
The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8-m Unit Telescopes ... more The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8-m Unit Telescopes (UT) and the four 1.8-m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in northern Chile. The two VLTI instruments, MIDI and AMBER deliver regular ...
The Very Large Telescope Interferometer (VLTI) on Cerro Paranal (2635 m) in Northern Chile reache... more The Very Large Telescope Interferometer (VLTI) on Cerro Paranal (2635 m) in Northern Chile reached a major milestone in September 2003 when the mid infrared instrument MIDI was offered for scientific observations to the community. This was only nine months after MIDI had ...
The author explains how the image quality at zenith could be brought from 1.2"- 1.3"to ... more The author explains how the image quality at zenith could be brought from 1.2"- 1.3"to less than 0.6"during test time over the last twelve months.
... nasa.gov BRKOVIC Alen Institut f or Astronomy ETH Zentrum CH-8092 Zurich CA Mats Institute of... more ... nasa.gov BRKOVIC Alen Institut f or Astronomy ETH Zentrum CH-8092 Zurich CA Mats Institute of Theoretical Astrophysics University of ... Ireland (UK) Jan Solar Department Astronomical Institute Slovak Academy of Sciences 059 60 Tatrcnska Lomnica ROVI Marta Instituto de ...
Abstract. We derive formulae for all parameters dening the eld astigmatism of misaligned two mirr... more Abstract. We derive formulae for all parameters dening the eld astigmatism of misaligned two mirror telescopes with arbitrary geometries and with stop positions any-where on the line connecting the vertices of the two mir-rors. The formulae show explicitly the dependence of the eld astigmatism on the fundamental design parameters and characteristics of the telescope and on the stop posi-tion. Special attention is given to the particular case where such a schiefspiegler has been corrected for coma at the eld center. In addition, we study the eects of the prac-tical denition that the center of the eld is the center of the adapter. Following a recent paper by McLeod, where the eld dependence of astigmatism is used to collimate a Ritchey-Chretien telescope with the stop at the primary mirror, we apply our formulae to the Cassegrain focus of the ESO Very Large Telescope (VLT), where the stop is at the secondary mirror and the telescope is only corrected for spherical aberration. We prese...
Advanced Wavefront Control: Methods, Devices, and Applications III, 2005
The future European Extremely Large Telescope will be composed of one or two giant segmented mirr... more The future European Extremely Large Telescope will be composed of one or two giant segmented mirrors (up to 100 m of diameter) and of several large monolithic mirrors (up to 8 m in diameter). To limit the aberrations due to misalignments and defective surface quality it is necessary to have a proper active optics system. This active optics system must
The images at the f/35 Cassegrain focus of the 3.6-m telescope have never been excellent. As the ... more The images at the f/35 Cassegrain focus of the 3.6-m telescope have never been excellent. As the system (c.f. [1]) was initially installed and used to do only aperture photometry, this was never an issue of major concern. In fact, it could not even be measured directly. Only with the advent of mid-infrared cameras (here TIMMI [2],[3]) the image quality could be measured easily and systematically. Several reports state that the avEMMI is now working smoothly and reliably. Through a well-deserved recognition of his merits, Pierre has now been hired as staff astronomer at the CanadaFrance-Hawaii Telescope. I take advantage of this occasion to welcome the newcomers, and to wish success in their new activitities to those who have left us. Erratum
The Very Large Telescope (VLT) Observatory on Cerro Paranal (2635 m) in Northern Chile is approac... more The Very Large Telescope (VLT) Observatory on Cerro Paranal (2635 m) in Northern Chile is approaching completion. After the four 8-m Unit Telescopes (UT) individually saw first light in the last years, two of them were combined for the first time on October 30, 2001 to form a stellar interferometer, the VLT Interferometer. The remaining two UTs will be integrated into the interferometric array later this year. In this article, we will describe the subsystems of the VLTI and the planning for the following years.
The Prefocal Station (PFS) is the last opto-mechanical unit before the telescope focal plane in t... more The Prefocal Station (PFS) is the last opto-mechanical unit before the telescope focal plane in the Extremely Large Telescope (ELT) optical train. The PFS distributes the telescope optical beam to the Nasmyth and Coudé instrument focal stations and it contains all of the sky metrology (imaging and wavefront sensing) that will be used by the active optics of the telescope and to support operations such as phasing the primary mirror (phasing and diagnostic station). It also hosts local metrology that will be used for coarse alignment and maintenance. We present the main results of a concept design study for the Nasmyth A prefocal station.
The Giant Magellan Telescope (GMT)1 is a 25 m telescope composed of seven 8.4 m “unit telescopes”... more The Giant Magellan Telescope (GMT)1 is a 25 m telescope composed of seven 8.4 m “unit telescopes”, on a common mount. Each primary and conjugated secondary mirror segment will feed a common instrument interface, their focal planes co-aligned and co-phased. During telescope operation, the alignment of the optical components will deflect due to variations in thermal environment and gravity induced structural flexure of the mount. The ultimate co-alignment and co-phasing of the telescope is achieved by a combination of the Acquisition Guiding and Wavefront Sensing system and two segment edge-sensing systems2. An analysis of the capture range of the wavefront sensing system indicates that it is unlikely that that system will operate efficiently or reliably with initial mirror positions provided by open-loop corrections alone3. The project is developing a Telescope Metrology System (TMS) which incorporates a large number of absolute distance measuring interferometers. The system will align optical components of the telescope to the instrument interface to (well) within the capture range of the active optics wavefront sensing systems. The advantages offered by this technological approach to a TMS, over a network of laser trackers, are discussed. Initial investigations of the Etalon Absolute Multiline Technology™ by Etalon Ag4 show that a metrology network based on this product is capable of meeting requirements. A conceptual design of the system is presented and expected performance is discussed.
The concept of "Virtual Image Slicer" was developed and implemented at the Very Large T... more The concept of "Virtual Image Slicer" was developed and implemented at the Very Large Telescope (VLT). The Virtual Image Slicer consists in elongating the stars in a given direction by the use of the Active Optics of the telescope. Alignment of the major axis of the elongated star along the entrance slit of the spectrograph allows to increase the total signal collected in a single (polarimetric) spectrum by a factor of up to 100 or more relative to a perfectly shaped image for bright sources.
The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8-m Unit Telescopes ... more The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8-m Unit Telescopes (UT) and the four 1.8-m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in northern Chile. The two VLTI instruments, MIDI and AMBER deliver regular ...
The Very Large Telescope Interferometer (VLTI) on Cerro Paranal (2635 m) in Northern Chile reache... more The Very Large Telescope Interferometer (VLTI) on Cerro Paranal (2635 m) in Northern Chile reached a major milestone in September 2003 when the mid infrared instrument MIDI was offered for scientific observations to the community. This was only nine months after MIDI had ...
The author explains how the image quality at zenith could be brought from 1.2"- 1.3"to ... more The author explains how the image quality at zenith could be brought from 1.2"- 1.3"to less than 0.6"during test time over the last twelve months.
... nasa.gov BRKOVIC Alen Institut f or Astronomy ETH Zentrum CH-8092 Zurich CA Mats Institute of... more ... nasa.gov BRKOVIC Alen Institut f or Astronomy ETH Zentrum CH-8092 Zurich CA Mats Institute of Theoretical Astrophysics University of ... Ireland (UK) Jan Solar Department Astronomical Institute Slovak Academy of Sciences 059 60 Tatrcnska Lomnica ROVI Marta Instituto de ...
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