Extreme M Dwarfs and Brown Dwarfs in a Deep CCD Survey

Extract

Two years ago, Seitzer and Tyson began a program of 4-meter prime focus CCD observations at CTIO, with the aim to develop techniques for imaging and photometry to the theoretical limit of that telescope and overall 52% efficiency: 26.6 J mag, 26 R mag, 25 I mag. Color-magnitude plots show that the limiting magnitudes for detection are 28 J mag, 27 R mag, and 25.3 I mag. Each of our CCD fields covers about 12 sq. arcmin., with total exposure time about 7000 sec. in each of the three bands (see Boeshaar and Tyson 1985). Processed images are put on a VAX 11/780 and the FOCAS v.3.2 automated detector and classifier is run. In order to determine the probability of detection and photometric errors as a function of magnitude, FOCAS is rerun many times on artificial images made by adding in real star and galaxy images, dimmed many magnitudes, at random locations on the CCD sky frame. Over 2000 objects are detected in every high galactic latitude CCD field, less than 50 of which are classified as stars. Most of the faint galaxies are very blue (due to evolution), making it possible to search for infrared excess stars in the presence of so many galaxies.