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 (AGWS) and two segment-edge-sensing systems2. An analysis of the capture range of the AGWS indicates that it is unlikely that that system will operate efficiently or reliably with initial mirror positions provided by open-loop corrections alone3.
Since 2016 GMT have been developing a telescope metrology system, that is intended to close the gap between openloop modelling and AGWS operations. A prototyping campaign was initiated soon after receipt of laser metrology hardware in 2017. This campaign is being conducted in collaboration with the Large Binocular Telescope Observatory (LBTO), and hardware was first deployed on the LBT in August 2017. Since that time the system had been run and developed over some hundreds of hours on-sky. It has been shown to be capable of reliably measuring the relative positions of the main optics over ~ 10 m to a repeatability of ~ 1-2 microns RMS. This paper will describe the prototyping campaign to date, the basic design of the system, lessons learned and results achieved. It will conclude with a discussion of future prototyping efforts.
The linear Atmospheric Dispersion Corrector has been operating at the SOuthern Astrophysical Research telescope since 2014. It was designed and built in collaboration between the University of North Carolina at Chapel Hill, and Cerro Tololo Inter-American Observatory. The device is installed in the elevation axis before the instruments mounted at the optical Nasmyth focus. It consists of two 300mm diameter sol-gel coated fused silica prisms, trombone mounted, which can be folded in or out of the beam. It is important for long slit spectroscopy, and essential for Multi-Object Slit spectroscopy. We present optical and mechanical designs, electronics and software control, and on-sky performance.
SAM (Soar Adaptive-optics Module), the SOAR (Southern Observatory for Astrophysical Research) GLAO facility is in service since 2011, with a UV, 355nm Laser Guide Star (LGS). The atmospheric wavefront error is therefore measured at 355nm and the star images are corrected in the visible range (BVRI bands). An ADC is required for High Resolution imaging at low telescope elevation, especially at shorter wavelengths of the visible spectrum. The ADC is based on 80mm diameter rotating prisms. This compact unit, fully automated, can be inserted or removed from the tightly constrained SAM collimated beam space-envelope, it adjusts to the parallactic angle and corrects the atmospheric dispersion. Here we present the optical and opto-mechanical design, the control design, the operational strategy and performance results obtained from extensive use in on-sky HR Speckle Imaging.
In recent years the V. M. Blanco 4-m telescope at Cerro Tololo Inter-American Observatory (CTIO) has been renovated for use as a platform for a completely new suite of instruments: DECam, a 520-megapixel optical imager, COSMOS, a multi-object optical imaging spectrograph, and ARCoIRIS, a near-infrared imaging spectrograph. This has had considerable impact, both internally to CTIO and for its wider community of observers. In this paper, we report on the performance of the renovated facility, ongoing improvements, lessons learned during the deployment of the new instruments, how practical operations have adapted to them, unexpected phenomena and subsequent responses. We conclude by discussing the role for the Blanco telescope in the era of LSST and the new generation of extremely large telescopes.
TripleSpec 4 (TS4) is a near-infrared (0.8um to 2.45um) moderate resolution (R ~ 3200) cross-dispersed spectrograph
for the 4m Blanco Telescope that simultaneously measures the Y, J, H and K bands for objects reimaged
within its slit. TS4 is being built by Cornell University and NOAO with scheduled commissioning in 2015.
TS4 is a near replica of the previous TripleSpec designs for Apache Point Observatory's ARC 3.5m, Palomar
5m and Keck 10m telescopes, but includes adjustments and improvements to the slit, fore-optics, coatings and
the detector. We discuss the changes to the TripleSpec design as well as the fabrication status and expected
sensitivity of TS4.
In an inauspicious start to the ultimately very successful installation of the Dark Energy Camera on the V. M. Blanco 4- m telescope at CTIO, the light-weighted Cer-Vit 1.3-m-diameter secondary mirror suffered an accident in which it fell onto its apex. This punched out a central plug of glass and destroyed the focus and tip/tilt mechanism. However, the mirror proved fully recoverable, without degraded performance. This paper describes the efforts through which the mirror was repaired and the tip/tilt mechanism rebuilt and upgraded. The telescope re-entered full service as a Ritchey- Chrétien platform in October of 2013.
To substantially upgrade the Blanco telescope a new Dark Energy Camera (DECam)5 was developed. The Blanco telescope was commissioned in 1974 before the benefits of modern heavy instruments were foreseen. Consequently, the mass of DECam is greater than the original instrument payload. DECam was installed on the Blanco in 20121, 2. The telescope mount was rebalanced about the declination assembly by redesigning the Cassegrain cage to accommodate a significant increase in balancing mass. Finite element analysis was used to both determine the structural integrity of the new telescope configuration and to predict the effects of this added mass on the relative displacement between the primary and secondary mirrors. The counterweight system is described.
The Dark Energy Camera (DECam) has been installed on the V. M. Blanco telescope at Cerro Tololo Inter-American Observatory in Chile. This major upgrade to the facility has required numerous modifications to the telescope and improvements in observatory infrastructure. The telescope prime focus assembly has been entirely replaced, and the f/8 secondary change procedure radically changed. The heavier instrument means that telescope balance has been significantly modified. The telescope control system has been upgraded. NOAO has established a data transport system to efficiently move DECam's output to the NCSA for processing. The observatory has integrated the DECam highpressure, two-phase cryogenic cooling system into its operations and converted the Coudé room into an environmentally-controlled instrument handling facility incorporating a high quality cleanroom. New procedures to
ensure the safety of personnel and equipment have been introduced.
The adaptive module of the 4-m SOAR telescope (SAM) has been tested on the sky by closing the loop on
natural stars. Then it was re-configured for operation with low-altitude Rayleigh laser guide star in early 2011.
We describe the performance of the SAM LGS system and various improvements made during one year of on-sky
tests. With acceptably small LGS spots of 1.6′′ the AO loop is robust and achieves a resolution gain of almost
two times in the I band, under suitable conditions. The best FWHM resolution so far is 0.25′′ over the 3′ field
of the CCD imager.
We present a progress report on the SOAR Adaptive Module, SAM, including some results of tests of the Natural
Guide Star mode: image correction in the visible, performance estimates, and experiments with lucky imaging.
We have tested methods to measure the seeing and the AO time constant from the loop data and compared
the results to those of the stand-alone site monitor. Measurements of the instrument throughput and telescope
vibrations are given. We report progress on the Laser Guide Star system implementation, including tests of the
UV laser, test of the beam transfer optics with polarization control. We present the designs of the laser launch
telescope and laser wavefront sensor.
The SOAR Adaptive Module (SAM) will compensate ground-layer atmospheric turbulence, improving image
resolution in the visible over a 3'x3' field and increasing light concentration for spectroscopy. Ground layer
compensation will be achieved by means of a UV (355nm) laser guide star (LGS), imaged at a nominal distance
of 10km from the telescope, coupled to a Shack-Hartmann wave front sensor (WFS) and a bimorph deformable
mirror. Unique features of SAM are: access to a collimated space for filters and ADC, two science foci, built-in
turbulence simulator, flexibility to operate at LGS distances of 7 to 14 km as well as with natural guide stars
(NGS), a novel APD-based two-arm tip-tilt guider, a laser launch telescope with active control on both pointing
and beam transfer. We describe the main features of the design, as well as operational aspects. The goal is to
produce a simple and reliable ground layer adaptive optics system. The main AO module is now in the integration
and testing stage; the real-time software, the WFS, and the tip-tilt guider prototype have been tested. SAM
commissioning in NGS mode is expected in 2009; the LGS mode will be completed in 2010.
The adaptive optics instrument for the SOAR 4.1-m telescope will
improve the spatial resolution by 2-3 times at visible wavelengths, over a field of 3 arcmin, by sensing and correcting low-altitude turbulence selectively. We will use a Rayleigh laser guide star to accomplish this. We present the laser guide star design with predictions of system performance based on real turbulence statistics and telescope properties, sky coverage and some opto-mechanical aspects of the AO module. Various design trade-offs are discussed.
We briefly describe the SOAR Optical Imager (SOI), the first light instrument for the 4.1m SOuthern Astronomical Research (SOAR) telescope now being commissioned on Cerro Pachón in the mountains of northern Chile. The SOI has a mini-mosaic of 2 2kx4k CCDs at its focal plane, a focal reducer camera, two filter cartridges, and a linear ADC. The instrument was designed to produce precision photometry and to fully exploit the expected superb image quality of the SOAR telescope over a 5.5x5.5 arcmin2 field with high throughput down to the atmospheric cut-off, and close reproduction of photometric pass-bands throughout 310-1050 nm. During early engineering runs in April 2004, we used the SOI to take images as part of the test program for the actively controlled primary mirror of the SOAR telescope, one of which we show in this paper. Taken just three months after the arrival of the optics in Chile, we show that the stellar images have the same diameter of 0.74" as the simultaneously measured seeing disk at the time of observation. We call our image "Engineering 1st Light" and in the near future expect to be able to produce images with diameters down to 0.3" in the R band over a 5.5' field during about 20% of the observing time, using the tip-tilt adaptive corrector we are implementing.
The SOAR Optical Imager (SOI) is the commissioning instrument for the 4.2-m SOAR telescope, which is sited on Cerro Pachón, and due for first light in April 2003. It is being built at Cerro Tololo Inter-American Observatory, and is one of a suite of first-light instruments being provided by the four SOAR partners (NOAO, Brazil, University of North Carolina, Michigan State University). The instrument is designed to produce precision photometry and to fully exploit the expected superb image quality of the SOAR telescope, over a 6x6 arcmin field. Design goals include maintaining high throughput down to the atmospheric cut-off, and close reproduction of photometric passbands throughout 310-1050nm. The focal plane consists of a two-CCD mosaic of 2Kx4K Lincoln Labs CCDs, following an atmospheric dispersion corrector, focal reducer, and tip-tilt sensor. Control and data handling are within the LabVIEW-Linux environment used throughout the SOAR Project.