HST photometry of the binary globular cluster Sersic 13N-S in NGC 5128

Abstract

Using Hubble Space Telescope archival images we resolved individual stars in two young globular clusters centered in the giant HII region Sersic 13, on the dust band of NGC 5128. We resolved 5 sources in the southern cluster and 4 sources in the northern one. The high U luminosity of these stars (-9.3 < M_F336W <-7.8) added to the previously detected WR features in the integrated spectra of the clusters suggest we are identifying the most massive stars of the clusters, with O or WR spectral types, whose masses can even reach 120 M_⊙. We have estimated their ages in t ≤ 6 × 10⁶ yr for comparison with two different set of isochrones, which is consistent with an scenario where the clusters form a binary pair that would merge in a short timescale.