A 32 Megapixel Dual Color CCD Imaging System

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Session 71 -- Instruments and Techniques
Oral presentation, Thursday, 10:30-12:00, Durham Room

[71.03] A 32 Megapixel Dual Color CCD Imaging System

S. Marshall, M. Pratt, C. Stubbs (CfPA/UCSB), C. Alcock, R. Allsman, T. Axelrod, D. Bennett, K. Cook, H.-S. Park (LLNL), C. Akerlof, S. Perlmutter, W. Sutherland (CfPA/UCB), K. Griest (CfPA/UCSD), K. Freeman, B. Peterson, P. Quinn, A. Rodgers (MSSSO)

We have developed an astronomical imaging system tailored to our search for gravitational microlensing by compact objects in the halo and disk of the Galaxy. The challenge of detecting rare microlensing events is to monitor ~10 million stars per night and distinguish genuine events from other sources of variability. The Large Magellanic Cloud and the Galactic bulge provide the high surface density of resolvable stars necessary for this task. A dedicated 50 inch telescope at Mt. Stromlo Observatory has been producing science data since fall 92. To achieve that capability our system incorporates eight 2048x2048 CCDs into two focal planes for simultaeous imaging in two passbands (4000-6400 and 6400-8000 $\AA$). Each focal plane consists of four "edge-buttable" CCDs in a custom mounted 2x2 array. The 0.62 arcsecond pixel scale (15$\mu$m) yields a 40 arcmin square field of view in each frame. A sophisticated point spread fitting photometry package (SODOPHOT, D. Bennett) extracts up to 350,000 useful magnitudes per color. The data collection rate needed is obtained by simultaneously reading out all sixteen CCD outputs (two per chip) at 34 KHz with 16 bit digitization. With exposure times of 150-300 seconds and a 70 second readout time we can collect up to 100 fields per night. These rates are designed to detect or rule out massive compact halo objects (MACHOs) in the $10^{-3}-10^{-1}$ $M_{\sun}$ range at densities well below the halo density. In addition they allow confident upper limits for the $10^{-6}-10^{0}$ $M_{\sun}$ range.

Thursday program listing