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
The WIYN Consortium is building the One Degree Imager (ODI) for its 3.5m telescope, located at Kitt Peak, Arizona
(USA). ODI will utilize both the excellent image quality and the one degree field of view of the WIYN telescope. Image
quality will be actively improved by localised tip/tilt image motion stabilisation using a novel concept of Orthogonal
Transfer Array (OTA) CCDs, which are a new detector type jointly developed with the PanSTARRS project. Its anticipated
median image quality of ≤ 0.55" in the R band will make ODI a unique and competitive instrument in the landscape of the
next generation of large field imagers.
A conceptual design of ODI was presented earlier at SPIE.<sup>1</sup> In the meantime, this concept matured, the ODI project has
been fully funded, and it has entered the construction phase. A prototype camera (QUOTA) with a field of view of 16'x16'
has already seen first star light in fall 2006. In this paper we report on the evolution of ODI's definition, the design of its
components, the status of the OTA detector development, and the path towards first light in early 2010. In accompanying
papers we detail the design of the ODI's optical corrector, the mechanical structures, and the software & instrument system
The main advantage of the WIYN One Degree Imager (ODI) over other wide-field imagers will be its exceptional image quality. The fine pixel scale (0.11") provides uncompromised sampling of stellar PSFs under most conditions (seeing >0.3"). The telescope routinely delivers the site seeing (median ~ 0.7") which is often below 0.5" FWHM, and can be as low as 0.25". The ODI specifications require the optics to maintain native high quality images. A two-element, fused silica, corrector meets the geometric error budget of 0.10" images, but the first element requires a mildly aspheric surface. The other element serves as the dewar window. A pair of cemented prisms (fused silica plus PBL6Y) serve as an ADC, which is essential to meet the image quality requirements for many observing programs. We describe the optical design details and its performance, the tolerances required, and the trade-offs considered for anti-reflection coatings. This paper is an update to a preliminary three-element design.
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 Jacoby<sup>1</sup> describes ODI's optical design, Yeatts<sup>2</sup> describes the software and control system
design, and Harbeck<sup>3</sup> gives a general update on the project.
The science case for wide fields on ELTs is well developed and justifies the implementation of 20 arc-minute and larger fields-of-view with seeing-limited performance on a 20 to 30-meter telescope. However, the practical implementation of a wide field can prove to be challenging with classical telescope design when low-thermal emissivity performance is also being optimized. Segmented mirrors assemblies need not be full aperture, axially symmetric structures. Space for secondary, tertiary, and quaternary mirror support structures that do not cross the optical path can be achieved with off-axis mirror assemblies. Barden, Harmer, Claver, and Dey described a 4-mirror, 1-degree FOV 30-meter telescope. We take that concept further with an off-axis approach. Three conic mirrors are required to produce excellent image quality in the 1-degree FOV (diffraction limited across the central few arc-minutes, better than 0.3" imaging performance at the edge of the field). A flat quaternary mirror is utilized both as a beam steering mirror to different instrument ports on the lower side of the telescope and as an adaptive mirror for wind-buffeting and possible ground layer AO correction. The final f/2.2 focal ratio allows the use of an echidna-style fiber positioner for very dense target field acquisition. Extreme AO and Ground Layer AO ports can both be implemented as well. Diffraction characteristics may possibly be improved given the lack of a spider mount for the secondary mirror but will be elliptical rather than circular.
We report on the performance of FLAMINGOS, the world's first fully cryogenic near-IR multi-object spectrometer. FLAMINGOS has a fast all refractive optical system, which can be used at telescopes slower than f/7.5. This makes FLAMINGOS a very efficient wide-field imager when used on fast small aperture telescopes and a high AW spectrometer using laser machined aperture masks for MOS spectroscopy. FLAMINGOS uses a 2048x2048 HgCdTe HAWAII-2 array by the Rockwell Science Center. The array is readout through 32 amplifiers, which results in low overheads for observations. We describe both the operating characteristics of the HAWAII-2 array and of the array controller and data acquisition system. FLAMINGOS has been in operation for about 1.5 years and is now in routine use on four telescopes: The Kitt Peak 4-m and 2.1-m, The 6.5-m MMT and the 8-m Gemini South Telescope. We will describe the operating characteristics of FLAMINGOS on each of these telescopes that deliver fields-of-view from 21x21 arcminutes to 2.7x2.7 arcminutes and pixels from 0.6 arcseconds to 0.08 arcseconds. While providing a large AW product for fast telescopes (i.e. f/8), FLAMINGOS becomes progressively less efficient on slower telescopes. Since nearly all large telescopes have fairly slow optical systems (f/12 or slower) the combination of large aperture and slow optical systems makes FLAMINGOS ill suited for optimal performance on current large aperture telescopes. Thus, we are beginning construction of FLAMINGOS-2, which will be optimized for performance on the f/16 Gemini South 8-m telescope. Similar to FLAMINGOS, FLAMINGOS-2 will be fully refractive using grisms, laser machined aperture masks and a 2048x2048 HgCdTe HAWAII-2 array. FLAMINGOS-2 will provide a 6.1 arcminute field-of-view with 0.18 arcsecond pixels. FLAMINGOS-2 will also be designed to except an f/32 beam from the Gemini South MCAO system.
The optical design for the WIYN One Degree Imager (ODI) is based on well-known princples for the design of secondary focus correctors of Ritchey-Chrétien telescopes. It started as the classical two element plus/minus pair of lenses required to correct moderate and wide fields of view whilst working with wide spectral regions. However, since this corrector is required to cover a one degree square and plane field of view, accommodate filters and an atmospheric dispersion compensator, it evolved into three elements. In order to avoid the addition of more glass than was absolutely necessary the third element was designed to serve the dual function of field flattener and dewar window. The final form presented here is plus/minus/minus in power distribution with well-separated elements. The ADC is situated between the first and second elements with filter between the second and third elements in an accessible position. Theoretically the worst-case image given is 90% of the ensquared energy into 2 by 2 pixels in the corner of the one degree square field.
The WIYN One Degree Imager (ODI) will be a well-sampled (0.11” per pixel) imager that provides a full one degree square field of view (32K×32K pixels). ODI will utilize high resistivity, red sensitive, orthogonal transfer (OT) CCDs to provide rapid correction for image motion arising from telescope shake, guider errors, and atmospheric effects. ODI will correct the full field of view by deploying 64 array packages having a total of 4096 independently controllable OTCCDs that can correct individually for local (2 arcmin) image motion. Each array package is an orthogonal transfer array (OTA) of 64 CCDs arranged in an 8×8 grid. Each CCD has 512×512 pixels. We expect the median image quality at the WIYN 3.5m telescope in RIZ to be 0.52”, 0.43”, and 0.35” FWHM. ODI makes optimal use of the WIYN telescope, which has superb optics, excellent seeing characteristics, a natural 1.4 degree field of view (with a new corrector), and can serve as a pathfinder for LSST in terms of detectors, data pipelines, operations strategies, and scientific motivation.
The National Optical Astronomy Observatory is developing a new, wide-field, imaging spectrograph for use on its existing 4-meter telescopes. This Next Generation Optical Spectrograph (NGOS) will utilize volume-phase holographic grating technology and will have a mosaiced detector array to image the spectra over a field of view that will be something like 10.5 by 42 arc-minutes on the sky. The overall efficiency of the spectrograph should be quite high allowing it to outperform the current RC spectrograph by factors of 10 to 20 and the Hydra multi-fiber instrument by a facto of fiber to ten per object. The operational range of the instrument will allow observations within the optical and near-IR regions. Spectral resolutions will go from R equals 1000 to at least R equals 5000 with 1.4 arc-second slits. The large size of this instrument, with a beam diameter of 200 mm and an overall length of nearly 3 meters, presents a significant challenge in mounting it at the Cassegrain location of the telescope. Design trades and options that allow it to fit are discussed.
We are exploring the feasibility of a very large telescope with a wide field of view for multi-object spectroscopic surveys. This paper presents a brief overview of the scientific need for such facility, a possible optical design for such a telescope, and a description of how such a telescope might function for both wide-field, seeing-limited spectroscopy and narrow-field, high-Strehl imaging and spectroscopy. The science is primarily driven by the fact that imaging surveys are now capable of cataloguing vast numbers of targets that would take a formidable amount of time on currently existing telescopes for spectroscopic followup. The telescope design, a 4-mirror extension of the Paul concept, is a 30-meter telescope that delivers a full 1 degree(s) field at f/4 with excellent image performance across the full field. The primary is an f/1, 30-meter. The secondary has a diameter of 5.3-meters and contains a pure conic surface that delivers an uncorrected focus between the primary and secondary. The tertiary mirror is located at the vertex of the primary and has a diameter of about 10.6- meters. The quaternary mirror, located at the position of the initial focus, is about 4.4-meters and images the final focus back at the vertex of the tertiary mirror. The initial design had both the tertiary and quaternary mirrors with high-order, even aspheric surfaces. Further study has led to a simplification of the design in which the tertiary is now a pure conic like the primary and secondary mirrors, and the quaternary mirror is something like a Schmidt corrector with only modest fourth and sixth order terms.
The confluence of advances in telescope and spectrograph design computing power, pathfinding imaging capabilities on the ground and in space, and the maturity of many astrophysical fields, allow us to look beyond the study of a few unique objects and towards the systematic study of large samples in order to completely characterize their properties, formation history, and cosmological significance. These studies require spectroscopic observations to probe the kinematics, chemical composition, dynamics, ages, masses and evolutionary histories of astronomical objects. Examples of three fundamental science goals are described that demand a wide-field system on a large telescope.
The design of a near-IR spectrometer for the Gemini 8m telescopes is described. This instrument, GNIRS, provides coverage from 0.9 to 5.5 micrometers at several spectral resolutions and two pixel scales. Capabilities include an imaging mode intended primarily for acquisition, a cross- dispersed mode covering wavelengths from 0.9 to 2.5 micrometers , and provisions for an integral field unit. The design of the GNIRS is conservative, as it must meet tight schedule and resource constraints; it nonetheless provides high throughput and operational efficiency, minimal flexure, and the flexibility needed to support queue observing. The optics are a combination of diamond-turned metal optics for the fore-optics and collimator, and refractive optics for the cameras. The mechanism include a two-axis grating turret; all mechanism are deposited by means of internal detents. The instrument achieves low flexure within its weight budget by the use of a modular structure composed of cylindrical light-weighted sections into which individual mechanisms and optics modules are mounted. Extensive analyses of mechanical and optical performance have been performed. The GNIRS has passed its critical design review, and fabrication is now underway.