A G1-like Globular Cluster in NGC 1023

The structure of a very bright ( M V = -10.9) globular cluster in NGC 1023 is analyzed on two sets of images taken with the Hubble Space Telescope . From careful modeling of King profile fits to the cluster image, a core radius of r c = 0.55 ± 0.1 pc, effective radius R e = 3.7 ± 0.3 pc, and a central surface brightness of μ 0 ( V ) = 12.9 ± 0.5 mag arcsec -2 are derived. This makes the cluster much more compact than ω Cen, but very similar to the brightest globular cluster in M31, G1 (= Mayall II). The cluster in NGC 1023 appears to be very highly flattened with an ellipticity of ≈ 0.37, even higher than for ω Cen and G1, and similar to the most flattened clusters in the Large Magellanic Cloud.