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Sofia Feltzing. Profile photo.

Sofia Feltzing


Sofia Feltzing. Profile photo.

A photometric and spectroscopic study of the new dwarf spheroidal galaxy in Hercules. Metallicity, velocities and a clean list of RGB members


  • Daniel Adén
  • Sofia Feltzing
  • A. Koch
  • M.I. Wilkinson
  • E.K. Grebel
  • Ingemar Lundström
  • G.F. Gilmore
  • D.B. Zucker
  • V. Belukurov
  • N.W. Evans
  • Daniel Faria

Summary, in English

Our aim is to provide as clean and as complete a sample as possible of red giant branch stars that are members of the Hercules dSph galaxy. With this sample we explore the velocity dispersion and the metallicity of the system. Stromgren photometry and multi-fibre spectroscopy are combined to provide information about the evolutionary state of the stars (via the Stromgren c_1 index) and their radial velocities. Based on this information we have selected a clean sample of red giant branch stars, and show that foreground contamination by Milky Way dwarf stars can greatly distort the results. Our final sample consists of 28 red giant branch stars in the Hercules dSph galaxy. Based on these stars we find a mean photometric metallicity of -2.35 dex which is consistent with previous studies. We find evidence for an abundance spread. Using those stars for which we have determined radial velocities we find a systemic velocity of 45.2 km/s with a dispersion of 3.72 km/s, this is lower than values found in the literature. Furthermore we identify the horizontal branch and estimate the mean magnitude of the horizontal branch of the Hercules dSph galaxy to be V_0=21.17, which corresponds to a distance of 147 kpc. We have shown that a proper cleaning of the sample results in a smaller value for the velocity dispersion of the system. This has implications for galaxy properties derived from such velocity dispersions.


  • Lund Observatory

Publishing year







Astronomy & Astrophysics





Document type

Journal article


EDP Sciences


  • Astronomy, Astrophysics and Cosmology


  • galaxies: fundamental parameters
  • galaxies: dwarf
  • galaxies:
  • individual: Hercules
  • galaxies: kinematics and dynamics
  • photometry



Research group

  • Observational and Theoretical Astrophysics


  • ISSN: 0004-6361