DDO photometry of M71: Carbon and nitrogen patterns among evolving giants

We present V, B-V, and DDO C(41-42) and C(42-45) photometry for a sample of 75 red giants down to M-v = +2 in the relatively metal-rich Galactic globu lar cluster M71. The C(41-42) colors reveal a bimodal distribution of CN ba nd strengths generally anticorrelated with CH band strength as measured by the C(42-45) color. Both DDO colors agree well with those found in 47 Tucan ae, a nearby globular cluster of similar metallicity, and suggest nearly id entical C and N abundance patterns among the giants of both clusters. A com parison with synthetic DDO colors demonstrates that little change in surfac e C or N abundance is required to match the colors of the M71 giants over t he entire luminosity range observed. Apparently like 47 Tuc (a cluster of m uch greater mass and central concentration), M71 exhibits an abundance patt ern that cannot be solely the result of internal mixing.