John McGraw (The University of New Mexico), Mark R. Ackermann (The University of New Mexico), Tom Williams (The University of New Mexico), Peter C. Zimmer (The University of New Mexico), Walter Gerstle (The University of New Mexico) G. Fritz Benedict (The University of Texas), Stephen C. Odewahn (The University of Texas), Lt. Col. Charles J. Wetterer (US Air Force Academy), Victor L. Gamiz (AFRL/DE), Lt. Eric Golden (AFRL/DE), Charles F. Claver (National Optical Astronomy Observatory), Jeffrey R. Pier (US Naval Observatory, Flagstaff), Dean C. Hines (Space Science Institute)
Keywords: Telescopes, Instrumentation
Abstract:
Precision ground-based photometric and astrometric measurements enable new astrophysical research programs and new capabilities in faint object detection and characterization for low Earth orbit (LEO) and geosynchronous transfer orbit (GTO) satellites. The CCD/Transit Instrument with Innovative Instrumentation (CTI-II) is the second generation of a 1.8-m stationary, meridian pointing telescope fundamentally capable of millimagnitude photometry and milliarcsecond astrometry. The optical design for this telescope is complete, and an innovative focal plane mosaic including real-time focus feedback is being finalized. We discuss the telescope system design considerations, support instrumentation and calibration techniques that allow this precision, even for measurements made through Earths turbulent and turbid atmosphere. Ancillary instrumentation includes optical and structural metrology and monitoring instruments, an atmospheric extinction lidar and a system of cameras capable of providing real-time extinction measurements.
The stationary, fully automated CTI-II uses the time-delay and integrate (TDI) readout mode (operated at the sidereal rate) on a mosaic of CCD detectors to nightly generate a five bandpass, 1° wide (declination) image, nominally 120° long (corresponding to observing for an eight-hour night) strip image of the sky to limiting magnitudes fainter than 21 per bandpass. After one year CTI-II will have completed observation of a small circle on the sky at a declination of +28°.
The CTI-II data, approximately 200 Gbytes nightly, will enable a large number of astrophysical research programs including Galactic astronomy based upon motions and parallaxes of stars in the solar neighborhood, discovery and synoptic monitoring of variability in the cores of galaxies, and the discovery of targets of opportunity based upon either luminosity variability (e.g. supernovae) or motion (e.g. asteroids).
The same database can be used to construct a calibrated, homogeneous photometric and astrometric catalog for northern hemisphere observers. Multi-night observations are combined to exclude variable stars, enhance the precision of photometry and refine the positions and motions of more than 106 stars distributed in a strip continuous in RA and 1° wide in declination. Multi-year observations allow production of precision astrometry and photometry, and result in a system of faint photometric and astrometric standard stars useful to northern observers of the sky, including past, current and future large-scale surveys such as the Sloan Digital Sky Survey, Pan-STARRS and the Large Synoptic Survey Telescope. The always observable strip of standard stars will be useful for optical sky surveillance systems, in general.
CTI-II is being designed and implemented as part of the Near Earth Space Surveillance Initiative (NESSI), which will link CTI-II to the Hobby-Eberly Telescope at McDonald Observatory, a giant special-purpose spectroscopic telescope capable of obtaining a spectrum of any target of opportunity and synoptically monitoring any object discovered by CTI-II. NESSI is funded by AFRL.
Date of Conference: September 10-14, 2006
Track: Telescopes and Instrumentation