The StarScan Plate Measuring Machine: Overview and Calibrations

Abstract

The StarScan machine at the U.S. Naval Observatory (USNO) completed measuring photographic astrograph plates to allow determination of proper motions for the USNO CCD Astrograph Catalog (UCAC) program. All applicable 1940 AGK2 plates, about 2200 Hamburg Zone Astrograph plates, 900 Black Birch (USNO Twin Astrograph) plates, and 300 Lick Astrograph plates have been measured. StarScan comprises of a CCD camera, telecentric lens, air-bearing granite table, stepper motor screws, and Heidenhain scales to operate in a step-stare mode. The repeatability of StarScan measures is about 0.2 µm. The CCD mapping as well as the global table coordinate system has been calibrated using a special dot calibration plate and the overall accuracy of StarScan x, y data is derived to be 0.5 µm. Application to real photographic plate data shows that position information of at least 0.65 µm accuracy can be extracted from course grain 103a-type emulsion astrometric plates. Transformations between "direct" and "reverse" measures of fine grain emulsion plate measures are obtained on the 0.3 µm level per well exposed stellar image and coordinate, which is at the limit of the StarScan machine.

A new astrometric reduction of photographic plates using the DAMIAN digitizer: improving the dynamics of the Jovian system

“…The fitted object positions in different digitizations (7 μm × 7 μm pixels) of the same test plate were found to repeat within 0.07 μm. These results are even better than previously obtained from the StarScan machine at USNO (Zacharias et al 2008).…”

Proper-Motion Study of the Magellanic Clouds Using SPM Material

“…For more details about the PMM setup and operations see Monet et al (2003). In a collaboration between the USNO-Washington and the Yale Astrometry Group, the StarScan reduction pipeline (Zacharias et al 2008) was modified to analyze the PMM pixel data of the SPM plates to produce a list of detections, image centers and photometric indices. The astrometric and photometric reductions then proceeded as follows: 1) cross-identification of detections to an input catalog, including 2) recognition and identification of central and higher grating orders; 3) photometric calibration to obtain BV ; 4) correction for Atmospheric Refraction; 5) correction for Magnitude Equation, which also combines grating-order systems; 6) transformation of short-exposure positions into the long-exposure system; and 7) astrometric solution into Tycho-2 to obtain (α, δ).…”

The NAROO digitization center

“…The repeatability, how closely the XY-table can return to an initial position following movement over the entire XY-axes, was also measured by the manufacturer with a capacitance up to 40 nm. These results are even better than those previously obtained from the StarScan machine at USNO (Zacharias et al 2008), and the DAMIAN machine at ROB (Robert et al 2011). In order to reach and maintain a high geometric and radiometric accuracy, the digitizer is placed in an overpressure, air-conditioned, ISO-5 clean room, at a temperature of 20°C ± 0.1°C and a relative humidity of 50% RH ± 5% RH.…”

“…According to the definition given by Zacharias et al (2008), the comparison between various measurements of the same dot and in the same measurement orientation reflects the absolute repeatability of the NAROO machine. One can use even a dot calibration plate DCP or real photographic plate data, without any assumptions on the errors of the photographic material since the measurement conditions and methods used remain the same for the comparison set.…”