Dan Blanco

Wide-field telescope design for the KMTNet project

The Korea Astronomy and Space Science Institute (KASI) are under development three 1.6m optical telescopes for the Korea Micro-lensing Telescope Network (KMTNet) project. These will be installed at three southern observatories in Chile, South Africa, and Australia by middle 2014 to monitor dense star fields like the Galactic bulge and Large Magellanic Cloud. The primary scientific goal of the project is to discover numerous extra-solar planets using the gravitational micro-lensing technique. We have completed the final design of the telescope. The most critical design issue was wide-field optics. The project science requires the Delivered Image Quality (DIQ) of less than 1.0 arcsec FWHM within 1.2 degree radius FOV, under atmospheric seeing of 0.75 arcsec. We chose the prime-focus configuration and realized the DIQ requirement by using a purely parabolic primary mirror and four corrector lenses with all spherical surfaces. We present design results of the wide-field optics, the primary mirror coating and support, and the focus system with three linear actuators on the head ring.

WIYN Bench Upgrade: a revitalized spectrograph

We describe the redesign and upgrade of the versatile fiber-fed Bench Spectrograph on the WIYN 3.5m telescope. The spectrograph is fed by either the Hydra multi-object positioner or integral-field units (IFUs) at two other ports, and can be configured with an adjustable camera-collimator angle to use low-order and echelle gratings. The upgrade, including a new collimator, charge-coupled device (CCD) and modern controller, and volume-phase holographic gratings (VPHG), has high performance-to-cost ratio by combining new technology with a system reconfiguration that optimizes throughput while utilizing as much of the existing instrument as possible. A faster, all-refractive collimator enhances throughput by 60%, nearly eliminates the slit-function due to vignetting, and improves image quality to maintain instrumental resolution. Two VPH gratings deliver twice the diffraction efficiency of existing surface-relief gratings: A 740 l/mm grating (float-glass and post-polished) used in 1st and 2nd-order, and a large 3300 l/mm grating (spectral resolution comparable to the R2 echelle). The combination of collimator, high-quantum efficiency (QE) CCD, and VPH gratings yields throughput gain-factors of up to 3.5.

The new MMT

Originally commissioned in 1979, the Multiple Mirror Telescope was a highly innovative and successful facility that pioneered many of the technologies that are used in the new generation of 8 to 10 m class telescopes. After 19 years of operations the MMT was decommissioned in March of 1998: the enclosure was modified, the optics support structure was replaced, and a single 6.5-meter primary mirror was installed and aluminized in-situ. First light for the new MMT was celebrated on May 13, 2000. Operations began with an f/9 optical configuration compatible with existing instruments. Work has continued commissioning two new optical configurations that will serve a suite of new instruments: an f/15 deformable secondary mirror and adaptive optics facility that has obtained diffraction-limited images; and an f/5.4 secondary mirror and refractive corrector that provides a one-degree diameter field of view. The wide-field instrument suite includes two fiber-fed bench spectrographs, a robotic fiber positioner, and a wide-field imaging camera.

Development of the Primary Mirror Segment Support Assemblies for the Thirty Meter Telescope

This paper describes the studies performed to establish a baseline conceptual design of the Segment Support Assembly (SSA) for the Thirty Meter Telescope (TMT) primary mirror. The SSA uses a combination of mechanical whiffletrees for axial support, a central diaphragm for lateral support, and a whiffletree-based remote-controlled warping harness for surface figure corrections. Axial support whiffletrees are numerically optimized to minimize the resulting gravityinduced deformation. Although a classical central diaphragm solution was eventually adopted, several lateral support concepts are considered. Warping harness systems are analyzed and optimized for their effectiveness at correcting second and third order optical aberrations. Thermal deformations of the optical surface are systematically analyzed using finite element analysis. Worst-case performance of the complete system as a result of gravity loading and temperature variations is analyzed as a function of zenith angle using an integrated finite element model.

The WIYN one degree imager: project update 2010

The One Degree Imager will be the future flagship instrument at the WIYN 3.5m observatory, once commissioned in 2011. With a 1 Gigapixel focal plane of Orthogonal Transfer Array CCD devices, ODI will be the most advanced optical imager with open community access in the Northern Hemisphere. In this talk we will summarize the progress since the last presentation of ODI at the SPIE 2008 meeting, focusing on optics procurement, instrument assembly and testing, and detector operations.

Performance and control of the MMT thermal system

We present results from a study of the performance of the MMT thermal system. The 6.5-m MMT primary mirror consists of a borosilicate honeycomb structure that is thermally controlled with a forced-air ventilation system. We will give an overview of both the measurement and control systems. Our goal is to define an algorithm for control of the ventilation system such that the primary mirror temperature closely tracks ambient while minimizing thermal gradients. Future work will include a study of correlations between the thermal state of the primary mirror and both seeing and wavefront errors. The thermal system is currently controlled by the telescope operators, but the results from this work will assist in fully automating the system.

The upgraded WIYN bench spectrograph

We present the as-built design overview and post-installation performance of the upgraded WIYN Bench Spectrograph. This Bench is currently fed by either of the general-use multi-fiber instruments at the WIYN 3.5m telescope on Kitt Peak, the Hydra multi-object positioner, and the SparsePak integral field unit (IFU). It is very versatile, and can be configured to accommodate low-order, echelle, and volume phase holographic gratings. The overarching goal of the upgrade was to increase the average spectrograph throughput by ~60% while minimizing resolution loss (< 20%). In order to accomplish these goals, the project has had three major thrusts: (1) a new CCD was provided with a nearly constant 30% increase is throughput over 320-1000 nm; (2) two Volume Phase Holographic (VPH) gratings were delivered; and (3) installed a new all-refractive collimator that properly matches the output fiber irradiance (EE90) and optimizes pupil placement. Initial analysis of commissioning data indicates that the total throughput of the system has increased 50-70% using the 600 l/mm surface ruled grating, indicating that the upgrade has achieved its goal. Furthermore, it has been demonstrated that overall image resolution meets the requirement of <20% loss.

Mechanical design of the WIYN One Degree Imager (ODI)

The WIYN consortium is building the One Degree Imager (ODI) to be mounted to a Nasmyth port of the WIYN 3.5m telescope, located at Kitt Peak, Arizona (USA). ODI will utilize both the excellent image quality and the one-degree field of view that the telescope delivers. To accommodate the large field of view (~0.39m diameter unvignetted field with 0.54m across the diagonal of the one-degree-square, partially vignetted field), 0.6m-class optics are required. The ODI design consists of a two element corrector: one serves as a vacuum barrier to the cryostat, the other is an asphere; two independently rotating bonded prism pairs for atmospheric dispersion compensation (ADC); nine independently deployable filters via a simple pivoting motion; and a 971 mega-pixel focal plane consisting of 64 orthogonal transfer array (OTA) devices. This paper is an overview of the mechanical design of ODI and describes the optical element mounting and alignment strategy, the ADC & filter mechanisms, plus the focal plane. Additionally, the project status will be discussed. In accompanying papers Jacoby1 describes ODIs optical design, Yeatts2 describes the software and control system design, and Harbeck3 gives a general update on the project.

Estimating local seeing at the DCT facility

A thermal model of the Discovery Channel Telescope (DCT) was used to estimate the contribution of major sources of local seeing; shell seeing, dome seeing and mirror seeing. The model simulates a dynamic equilibrium over several day/night cycles taking into account the morphology of the facility, diurnal insolation and radiation to the night sky, local air temperature and humidity swings, wind and air flow through the facility, and infiltration from warm spaces within the facility. The model confirmed that the well ventilated design of the DCT facility will virtually eliminate dome seeing, but that shell seeing and mirror seeing could be major contributors to local seeing. These can be mitigated by the choice of an appropriate exterior coating, and by cooling the primary mirror.

Three wide-field telescopes with spherical primary mirrors

This paper presents three optical designs based on the work of Maurice Paul. Pauls three-mirror anastigmats produce well-corrected, distortion-free fields of view. His design equations can be solved for a spherical primary mirror with one limitation: the image field is curved. Adding all-spherical refractive field-flattening optics yields well-corrected, flat image-fields of two degrees angular diameter or more. These designs can be scaled to very large telescopes with current technology.