Hubble Space Telescope true color image of M15

A true color image of the central region of M15

The figure is a true color (24-bit) image of the central 9'' x 9'' region of M15 imaged on the PC1 CCD. The red, green, and blue intensities are proportional to the brightnesses in the V, B, and U bands, respectively. Bright red giant branch stars with B-V ~ 1.3 appear reddish orange while blue horizontal branch stars with B-V ~ 0 appear blue. A green cross marks the cluster center determined from the number-weighted centroid of stellar positions. The surface density of stars is clearly seen to increase towards the cluster center all the way in to radii less than 0.5 arcseconds. The X-ray source AC 211 is the very blue star located roughly 2'' north of the cluster center. There is a concentration of faint stars 0.3 arcseconds north-west of the cluster centroid. The triple star AC 214 is the white object 0.5 arcseconds east of the center; its three components appear blended together in this picture. (stellar PSF subtracted)

Figure 2 from the article Globlar Cluster Photometry with the Hubble Space Telescope, V. WFPC2 Study of M15's Central Density Cusp, AJ, 111, 267.

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