The extended structure of the remote cluster B 514 in M 31 Detection of extra - tidal stars ⋆ , ⋆ ⋆

Aims. We present a study of the density profile of the remote M31 globular cluster B514, obtained from HST/ACS observations. Methods. Coupling the analysis of the distribution of the integrated light with star counts we are able to reliably follow the profile of the cluster out to r ∼ 35 ′′ , corresponding to ≃ 130 pc. The profile is well fitted, out to ∼ 15 core radii, by a King Model having C=1.65. With an estimated core radius r c = 0.38 ′′ , this corresponds to a tidal radius of r t ∼ 17 ′′ (∼ 65 pc). The analysis of the light profile allows also the estimate of the ellipticity and position angle of the isophotes within r ≤ 20 ′′. Results. We find that both the light and the star counts profiles show a departure from the best fit King model for r > ∼ 8 ′′-as a surface brightness excess at large radii, and the star counts profile shows a clear break in correspondence of the estimated tidal radius. Both features are interpreted as the signature of the presence of extra tidal stars around the cluster. It is also shown that B514 has a half-light radius significantly larger than ordinary globular clusters of the same luminosity. In the M V vs. logr h plane, B514 lies in a region inhabited by peculiar clusters, like ω Cen, G1, NGC2419 and others, as well as by the nuclei of dwarf elliptical galaxies.