An adaptive optics system is being developed by the U. S. Naval Observatory based on commercial, off-the-shelf components. This AO system will be used to experimentally test the influence of AO correction on precision astrometry across a wider-than-conventional field.
The Orion program developed a 2048x2048 infrared focal plane using InSb PV diodes for detectors. Several of these focal planes have been produced. However, the yield of the original readout multiplexer was not up to expectations owing to unanticipated shorts in the fabrication process. Since these shorts occurred at the metal 1-metal 2 crossover points and there are over 9 million such crossovers, the design had to be modified to work around these problems. Thus the Orion II readout was developed. The work is being done at the Raytheon Vision Systems (RVS) division (most recently Raytheon Infrared Operations, but better known as SBRC) by many of the same people who created the Orion I and ALADDIN focal planes. The design is very similar to the Orion I design with the addition of circuitry to work around the effect of the metal 1-metal 2 shorts. In this paper we will discuss the unique design features of this device as well as present test data taken from the new devices.
In order to extend the US Naval Observatory (USNO) small-angle astrometric capabilities to near infrared wavelengths we have designed and manufactured a 1024 x 1024 InSb re-imaging infrared camera equipped with an array selected from the InSb ALADDIN (Advanced Large Area Detector Development in InSb) development
program and broadband and narrowband 0.8 - 3.8 μm filters. Since the USNO 1.55-m telescope is optimized for observations at visible wavelengths with an oversized secondary mirror and sky baffles, the straylight rejection capabilities of the ASTROCAM Lyot stop and baffles are of critical importance for its sensitivity and flat-
fielding capabilities. An Offner relay was chosen for the heart of the system and was manufactured from the same melt of aluminum alloy to ensure homologous contraction from room temperature to 77 K. A blackened cone was installed behind the undersized hole (the Lyot stop) in the Offner secondary. With low distortion, a well-sampled point spread function, and a large field of view, the system is well suited for astrometry. It is telecentric, so any defocus will not result in a change of image scale. The DSP-based electronics allow readout of the entire array with double-correlated sampling in 0.19 seconds, but shorter readout is possible with single sampling or by reading out only small numbers of subarrays. In this paper we report on the optical, mechanical, and electronic design of the system and present images and results on the sensitivity and astrometric stability obtained with the system, now operating routinely at the 1.55-m telescope with a science-grade ALADDIN array.
Orion is a program to develop a 2048x2048 infrared focal plane using InSb PV detectors. It is the natural follow-on to the successful Aladdin 1024x1024 program, which was the largest IR focal plane of the 90's. Although the pixels are somewhat smaller than Aladdin, the overall focal plane is over 50mm in size and for the present is the largest IR focal plane of the 21st century. The work is being done by Raytheon Infrared Operations (RIO but better known as SBRC) by many of the same people who created the Aladdin focal plane. The design is very similar to the successful Aladdin design with the addition of reference pixels to lower noise and drift effects in long integrations. So far we have made five focal plane modules with hybridized InSb detectors. In this paper we will discuss the unique design features of this device as well as present test data taken from these devices.
The MDM/Ohio State/ALADDIN IR Camera (MOSAIC) is a general purpose near IR imaging camera and medium-resolution long- slit spectrometer in use on the MDM 1.3-m and 2.4-m telescopes and the Kitt Peak 2.1-m and 4-m telescopes. In cooperation with NOAO and USNO, MOSAIC is one of the first general-purpose near-IR instruments available to the astronomical community that uses a first-generation 1024 X 512 ALADDIN InSb array, with the capability to use a full 1024 X 1024 array once one becomes available. MOSAIC provides tow imaging plate scales, and a variety of long- slit grism spectroscopic modes. This paper describes the general instrument design and capabilities, and presents representative scientific results.
The inherent non-linearity in the photometric response of NICMOS-3 HgCdTe arrays can lead to photometric calibration errors of 1-2 percent or more when using standard flattening and calibration techniques involving single flat-field exposures and mid-level exposures of standard sources for calibration. Furthermore, the useful dynamic range of the device must be restricted to achieve even this precision, since deviations from linearity are greatest at higher exposure levels. We describe a technique to digitally linearize NICMOS-3 images by interpolating within the characteristic response curve for each pixel as determined from a series of exposures of a flat screen. Using astronomical observations, we quantify the improvements that can be achieved in final photometric precision and useful dynamic range.
An IR camera based on a Rockwell 256 X 256 HgCdTe (NICMOS III) array has been recently acquired by the U.S. Naval Observatory as part of a program to evaluate the astrometric characteristics of current-generation IR arrays. Results of a pixel-by-pixel photometric evaluation of this HgCdTe device are presented. Overall, the array is of extremely high quality with less than 100 (0.2%) photometrically unusable pixels. With a fairly stringent photometric selection based on linearity and full well, the bad pixel count is about 420. The average pixel photometric response is linear to within about 1.6% rms over a range of 0 - 120,000 e-; using a quadratic relation reduces the calibration errors to under 1% rms. For comparison, the results of a similar test with a Texas Instruments TI800 X 800 CCD (a prototype of the HST WF/PC 1) are shown.