A G1-like Globular Cluster in NGC 1023

Abstract

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 μ₀(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 ɛ~0.37, even higher than for ω Cen and G1, and similar to the most flattened clusters in the Large Magellanic Cloud. Based on observations with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.