Kinematic study of the disrupting globular cluster Palomar 5 using VLT spectra

Details Kinematic study of the disrupting globular cluster Palomar 5 using VLT spectra Kinematic study of the disrupting globular cluster Palomar 5 using VLT spectra

2002-06-17

arxiv.org/abs/astro-ph/0206276v1

Astron.J. 124 (2002) 1497

Astronomy and Astrophysics

Astrophysics

29 pages including 10 figures, accepted for publication in the Astronomical Journal

Scientific paper

10.1086/342287

Wide-field photometric data from the Sloan Digital Sky Survey have recently revealed that the Galactic globular cluster Palomar 5 is in the process of being tidally disrupted (Odenkirchen et al. 2001). Here we investigate the kinematics of this sparse remote star cluster using high resolution spectra from the Very Large Telescope (VLT). Twenty candidate cluster giants located within 6 arcmin of the cluster center have been observed with the UV-Visual Echelle Spectrograph (UVES) on VLT-UT2. The spectra provide radial velocities with a typical accuracy of 0.15 km/s. We find that the sample contains 17 certain cluster members with very coherent kinematics, two unrelated field dwarfs, and one giant with a deviant velocity, which is most likely a cluster binary showing fast orbital motion. From the confirmed members we determine the heliocentric velocity of the cluster as -58.7 +- 0.2 km/s. The total line-of-sight velocity dispersion of the cluster stars is 1.1 +- 0.2 km/s (all members) or 0.9 +- 0.2 km/s (stars on the red giant branch only). This is the lowest velocity dispersion that has so far been measured for a stellar system classified as a globular cluster. The shape of the velocity distribution suggests that there is a significant contribution from orbital motions of binaries and that the dynamical part of the velocity dispersion is therefore still substantially smaller than the total dispersion. ... (abridged)

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