Volume 473, Number 2, October II 2007
|Page(s)||429 - 436|
|Section||Galactic structure, stellar clusters, and populations|
|Published online||23 July 2007|
Detection of extra-tidal stars
INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: [luciana.federici;michele.bellazzini;flavio.fusipecci;alberto.buzzoni; gianluigi.parmeggiani]@oabo.inaf.it; firstname.lastname@example.org
Accepted: 6 June 2007
Aims.We present a study of the density profile of the remote M 31 globular cluster B514, obtained from HST/ACS observations.
Methods.By coupling 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 . With an estimated core radius rc = 0.38″, this corresponds to a tidal radius of rt~ 17″ (~65 pc). The analysis of the light profile also allows an estimate of the ellipticity and position angle of the isophotes within r ≤ 20″.
Results.We find that both the light and the star-count profiles show a departure from the best-fit King model for r 8″ – as a surface brightness excess at large radii, and the star-count profile shows a clear break in the 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 significantly larger half-light radius than ordinary globular clusters of the same luminosity. In the MV vs. log rh plane, B514 lies in a region inhabited by peculiar clusters, like ω Cen, G1, NGC 2419 and others, as well as by the nuclei of dwarf elliptical galaxies.
Key words: galaxies: individual: M 31 / galaxies: star clusters / catalogs / galaxies: local group / stellar dynamics
Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute (STScI), which is operated by AURA, Inc., under NASA contract NAS 5-26555.
Table 5 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/473/429
© ESO, 2007
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