The main goal of the mirror coating process is to deposit a thin homogeneous layer of aluminum over the bare glass. This is a very delicate process, which involves careful cleaning, high vacuum, and controlled vaporization of the aluminum filaments, so many variables influence the final result. One of the problems is the aluminum drops that fall from the filaments during the fire due to the power difference between them. This work focuses on reducing this power variance between filaments by proposing a new busbar arrangement, which will improve the heating curve and reduce the occurrence of drops over the mirror.
The Southern Astrophysical Research (SOAR) 4.1m telescope, located in Cerro Pachón, Chile, has an active optics system that uses a Shack Hartmann wave front sensor to achieve optimal image correction and focus. This Calibration Wave Front Sensor (CWFS) has two detectors, one to acquire the star and the other to sense the wave front. In 2012 the acquisition camera failed, being replaced temporarily by an SBIG camera. We describe here a project to repair and upgrade the CWFS, extending the lifetime of this critical telescope component. The upgrade includes two new detectors and modifications to the existing software in order to communicate with the new cameras. Also, new mechanical supports were fabricated to mount the new cameras, and a new field flattener was designed for the acquisition camera. A laboratory rig with all the components was setup so to carry out extensive testing before installation on the telescope.
The SOAR telescope was designed to have a bare Aluminum coating. This coating is performed in the Gemini-South sputtering facility. Two coatings have been done on the SOAR mirror (2004 and 2009). On both occasions, the reflectivity obtained for the UV-blue were lower than the reflectivity of the nominal bare Aluminum. Various tests have been done during 2018 and 2019, in order to reach a higher reflectivity in the UV, including changes in the coating recipe. We report here the progress to date, the performance that we have reached and the problems we have faced in this 8-meter coating facility.
We describe the design and implementation of a fourth version of the TripleSpec near-infrared spectrograph (TSpec4). This version of the instrument was designed for and first implemented on the 4-m Blanco telescope on Cerro Tololo, and subsequently converted for use on the 4-m Southern Astrophysical Research (SOAR) Telescope on Cerro Pachon. Details of the changed opto-mechanical design and mounting arrangements are discussed. An updated data pipeline provides reduced spectra from the instrument. We describe the required modifications and the performance of both implementations of TSpec4.
The move from the Blanco to SOAR required changing from operation at a classical Cassegrain f/8 focus to operation at a Nasmyth f/16 focus. The SOAR mount also employs a rotator and required accommodation to a significantly different back-focal distance inside the instrument. These changes were implemented by modifying the instrument fore-optics which feeds light onto the slit at f/10.6. The spectrograph and slit viewer optics are unchanged. A dichroic reflects infrared light toward the instrument while passing visible light to a SOAR facility guider; this removes the shortest wavelengths from the spectra and in turn required modification of the data reduction pipeline.
As the telescopes have similar apertures, the performance of the instrument is similar on both, though on SOAR image quality is somewhat better and details of the instrument’s optical properties differ also. Flexure performance differs as well due to the different instrument locations.
The 4.1-m SOAR telescope needs fast tip-tilt guiding and active correction of focus and astigmatism to reach good image quality allowed by the excellent site seeing. A concept of the new guider with a 2×2 wavefront sensor is presented. It uses the X-Y positioning mechanism of the current guider, while the pick-off arm, camera, and detector are replaced by the new hardware. The pick-off arm has 2 positive lenses to collimate the beam, with an internal focus adjustment to compensate for focus offset in the science instrument and for the field curvature. The 4 spots are formed by a mirror with slightly tilted segments, located near the camera. The detector is an EM CCD; guiding on stars as faint as V=17 mag is possible using the correlation algorithm for centroiding; aberrations are measured on the averaged images. Results of the on-sky tests of the new guider prototype are presented.
The f/8 RC-Cassegrain Focus of the Blanco Telescope at Cerro Tololo Inter-American Observatory, hosts two new instruments: COSMOS, a multi-object spectrograph in the visible wavelength range (350 – 1030nm), and ARCoIRIS, a NIR cross-dispersed spectrograph featuring 6 spectral orders spanning 0.8 – 2.45μm. Here we describe a calibration lamp unit designed to deliver the required illumination at the telescope focal plane for both instruments. These requirements are: (1) an f/8 beam of light covering a spot of 92mm diameter (or 10 arcmin) for a wavelength range of 0.35μm through 2.5μm and (2) no saturation of flat-field calibrations for the minimal exposure times permitted by each instrument, and (3) few saturated spectral lines when using the wavelength calibration lamps for the instruments. To meet these requirements this unit contains an adjustable quartz halogen lamp for flat-field calibrations, and one hollow cathode lamp and four penray lamps for wavelength calibrations. The wavelength calibration lamps are selected to provide optimal spectral coverage for the instrument mounted and can be used individually or in sets. The device designed is based on an 8-inch diameter integrating sphere, the output of which is optimized to match the f/8 calibration input delivery system which is a refractive system based on fused-silica lenses. We describe the optical design, the opto-mechanical design, the electronic control and give results of the performance of the system.
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.
Free-atmosphere, and surface-layer optical-turbulence have been extensively monitored over the years. The
optical-turbulence inside a telescope enclosure en the other hand has yet to be as fully characterized. For this
latest purpose, an experimental concept, LOTUCE (LOcal TUrbulenCe Experiment) has been developed in
order to measure and characterise the so-called dome-seeing. LOTUCE2 is an upgraded prototype whose main
aim is to measure optical turbulence characteristics more precisely by minimising cross-contamination of signals.
This characterisation is both quantitative (optical turbulence strength) and qualitative (assessing the optical
turbulence statistical model). We present the new opto-mechanical design, with the theoretical capabilities and
limitations to the actual models.
Multi-object adaptive optics requires a tomographic reconstructor to compute the AO correction for scientific targets
within the field, using measurements of incoming turbulence from guide stars angularly separated from the science
targets. We have developed a reconstructor using an artificial neural network, which is trained in simulation only.
We obtained similar or better results than current reconstructors, such as least-squares and Learn and Apply, in
simulation and also tested the new technique in the laboratory. The method is robust and can cope well with
variations in the atmospheric conditions. We present the technique, our latest results and plans for a full MOAO experiment.
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