M. N. Ishigaki, N. Hwang, M. Chiba, W. Aoki

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15 Citations (Scopus)


We present Subaru/Faint Object Camera and Spectrograph and Keck/Deep Imaging Multi-Object Spectrometer medium-resolution spectroscopy of a tidally disrupting Milky Way (MW) globular cluster Palomar 5 (Pal 5) and its tidal stream. The observed fields are located to cover an angular extent of ∼17° along the stream, providing an opportunity to investigate a trend in line-of-sight velocities (V los) along the stream, which is essential to constrain its orbit and underlying gravitational potential of the MW's dark matter halo. A spectral fitting technique is applied to the observed spectra to obtain stellar parameters and metallicities ([Fe/H]) of the target stars. The 19 stars most likely belonging to the central Pal 5 cluster have a mean V los of-58.1 ± 0.7 km s-1 and metallicity [Fe/H] =-1.35 ± 0.06 dex, both of which are in good agreement with those derived in previous high-resolution spectroscopic studies. Assuming that the stream stars have the same [Fe/H] as the progenitor cluster, the derived [Fe/H] and values are used to estimate the possible V los range of the member stars at each location along the stream. Because of the heavy contamination of the field MW stars, the estimated V los range depends on prior assumptions about the stream's , which highlights the importance of more definitely identifying the member stars using proper motion and chemical abundances to obtain unbiased information of V los in the outer part of the Pal 5 stream. The models for the gravitational potential of the MW's dark matter halo that are compatible with the estimated V los range are discussed.

Original languageEnglish
Article number157
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 2016 Jun 1


  • globular clusters: individual (Palomar 5)
  • stars: abundances
  • stars: kinematics and dynamics Supporting material: machine-readable table


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