We present both laboratory and telescope testing results describing the performance of the H4RG-10 CMOS-Hybrid
detector. The H4RG-10 is the largest visible hybrid array currently in existence and shows great potential for use in
future space missions. We report read noise, dark current, pixel connectivity, persistence, and inter-pixel
capacitance measurements for the temperature range 110-240 K. We report on quantitative astrometric and
qualitative photometric performance of the instrument based on observations made at USNO's Flagstaff Station
observatory and establish an upper limit to the astrometric performance of the detector. We discuss additional
testing and future work associated with improving detector performance.
CMOS-based focal planes have many potential advantages over CCDs for use in space for star mapping/star
tracking applications. These include more flexible readout circuitry and improved radiation tolerance. There are
also weaknesses, including noise performance, quantum efficiency, and potential systematics introduced by the
presence of circuitry on the photosensitive side of the detector. In this paper, we measure the effects of these sources
of error on centroiding and photometry for the HDTV (1k x 2k) SI-1920HD camera by observing stellar reference
fields using USNO's 8-inch Twin Astrograph telescope in Flagstaff, AZ. This camera serves as an archetype for the
entire family of related TIS detectors, including the 3k x 4k V12M and the 7.6k x 7.6k V59M. We determine an
upper limit for the astrometric centroiding performance for this class of detector to be ~1/30th of a pixel. There are
indications that better performance may be possible if improvements are made to the temperature control system
used for this first set of observations.
A full-wafer, 10,580 × 10,560 pixel (95 × 95 mm) CCD was designed and tested at Semiconductor Technology
Associates (STA) with 9 μm square pixels and 16 outputs. The chip was successfully fabricated in 2006 at DALSA
and some performance results are presented here. This program was funded by the Office of Naval Research
through a Small Business Innovation in Research (SBIR) program requested by the U.S. Naval Observatory for
its next generation astrometric sky survey programs. Using Leach electronics, low read-noise output of the 111
million pixels requires 16 seconds at 0.9 MHz. Alternative electronics developed at STA allow readout at 20
MHz. Some modifications of the design to include anti-blooming features, a larger number of outputs, and use
of p-channel material for space applications are discussed.
The U.S. Naval Observatory Robotic Astrometric Telescope (URAT) project aims at a highly accurate (5 mas), ground-based, all-sky survey. Requirements are presented for the optics and telescope for this 0.85 m aperture, 4.5 degree diameter field-of-view, specialized instrument, which are close to the capability of the industry. The history of the design process is presented as well as astrometric performance evaluations of the toleranced, optical design, with expected wavefront errors included.
The Astrophysics of Reference Frame Tie Objects Key Science program will investigate the underlying physics of SIM grid objects. Extragalactic objects in the SIM grid will be used to tie the SIM reference frame to the quasi-inertial reference frame defined by extragalactic objects and to remove any residual frame rotation with respect to the extragalactic frame. The current realization of the extragalactic frame is the International Celestial Reference Frame (ICRF). The ICRF is defined by the radio positions of 212 extragalactic objects and is the IAU sanctioned fundamental astronomical reference frame. This key project will advance our knowledge of the physics of the objects which will make up the SIM grid, such as quasars and chromospherically active stars, and relates directly to the stability of the SIM reference frame. The following questions concerning the physics of reference frame tie objects will be investigated. What is the origin of optical emission in quasars? Are the optical photo-centers of quasars compact and positionally stable on the micro-arcsecond level? Are binary black hole mergers responsible for quasars? What is (are) the emission mechanism(s) responsible for generating radio emission in chromospherically active stars. What causes the transition of spherically symmetric Asymptotic Giant Branch (AGB) stars to asymmetric planetary nebulae (PNe)?
The current status and future developments of highly accurate, dense, astrometric surveys on the International Celestial Reference System (ICRS) are discussed. The U.S. Naval Observatory CCD Astrograph Catalog (UCAC) project is an ongoing, observational program aiming at a global sky coverage with 20 to 70 mas positional accuracy for the 10 to 16 mag range. This program extends the reference star density by a factor of about 30 over the Tycho-2 catalog, with about 10 times higher positional accuracy than the GSC I. The second UCAC release fall 2002) gives positions and proper motions for stars between -90 and about +40 degrees declination. The first release and unpublished updates have been supporting the Sloan Digital Sky Survey, 2MASS, the minor planet community, and SOAR. The next step, a 1-meter class, dedicated, robotic, wide-field, astrometric instrument is already designed (10k by 10k single CCD) and a global sky catalog to 20th magnitude could be observed in only 2 years with 10 mas accurate positions in the magnitude range between 15 to 18.
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