CCD PHOTOMETRY TO V = 21 IN A PUPPIS FIELD.

A UBV calibrating sequence of 235 stars brighter than V = 21.25 in the 'Puppis Window' at (l,b) = (254 deg, 0 deg) is presented. The photoelectric data were obtained during the night of October 3, 1983, using a CCD camera on the CTIO 4-m telescope. The program used consisted of 10-s and 120-s exposure pairs in B and V of a field centered on the Reed and FitzGerald (1983) star C7-53. After preprocessing the program frames (bias, flat-fielding, and fringe removal), the data were reduced with an operating version of DAOPHOT. The internal errors of the photometry, derived through DAOPHOT by adding scaled images scattered randomly throughout the frame and then remeasuring the frame, are summarized. The cutoff of V = 21.25 corresponds to the value of sigma(V,B) about 0.1 mag.