Photometry of Southern Globular Clusters-III: BRIGHT STARS IN 47 TUCANAE, NGC 6397 AND NGC 288

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Abstract
New photoelectric UBV data are presented for about 60 stars down to V = 16 in 47 Tuc, 80 stars to V = 16.5 in NGC 6397 and 50 stars to V = 17.5 in NGC 288. The 47 Tuc data agree well with recent work by Menzies, and indicate systematic errors in earlier photographic photometry; the majority of the 47 Tuc horizontal branch stars occupy a very small clearly defined region of the C–M diagram. NGC 6397 has a narrow well-defined giant branch, with only a few possible asymptotic branch stars or red horizontal branch stars; there are considerable systematic errors in the earlier RGO photographic photometry. NGC 288 is unusual in having a predominantly blue horizontal branch but apparently high metallicity according to several criteria; its reddening is E ( B−V ) = 0.04 mag and its apparent distance modulus is ( m − M ) ≈ 14.5. A comparison is made between these three clusters and two studied previously, ω Cen and NGC 6752, and four northern clusters studied extensively by Sandage. The interstellar reddenings, distances, ultraviolet excesses and other parameters are derived. Various metallicity parameters correlate well together, but several clusters violate the general correlation between metallicity and horizontal branch type by having purely blue horizontal branches irrespective of metallicity. NGC 288 is the most extreme example of this class, of which M13 is the prototype.

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