Abstract

Photometric data, positions, and finding charts are given for fifty-four variables in three astrograph fields covering 74 square degrees near the north galactic pole. The variables are in the magnitude range 12.7 <m= < 18.4 and the survey is judged to be essentially complete for RR Lyrae variables with amplitude (A) greater than 0.75 mag. and with < 17.0. Periods were derived for forty-six of these stars; forty-four are RR Lyrae variables and two are eclipsing systems. The period-amplitude relation of the RR Lyrae variables in the polar fields is better defined than for those in the field of lower latitude (b" = 30 ) discussed in Paper III. This is taken to mea that the polar variables belong to a more homogeneous population. An analysis is made of the space densities (p) of RR Lyrae variables of type a with A > 0.75 mag. and period greater than 0.44 days. The logarithmic gradient (3 log p/8z) is found to be -0.071 and -0.080 (where z is in kpc) for polar interstellar extinctions of 0.12 and 0.48 mag., respectively. These values are much smaller than the logarithmic gradient of -0.22 derived by Shapley (1939). A K force of about 3 X 10 cm (5 < z < 15 kpc) is found if the present density gradient is used instead of Shapley's in the derivation of K by the method of Oort and van Woerkom. It is estimated that the number of type a RR Lyrae variables with A > 0.75 mag. per 0.5 mag. interval in the magnitude range 18 <m < 20 is of the order of 0.050.12 per square degree.