Fabry-Perot observations of globular clusters. II. 47 TUC, NGC 6397, and M30

Karl Gebhardt, Carlton Pryor, T. B. Williams, James E. Hesser

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Using the Rutgers Imaging Fabry-Perot Spectrophotometer on the CTIO 4-m telescope, we have measured radial velocities for 548 stars in 47 Tuc (NGC 104), 128 stars in NGC 6397, and 132 stars in M30 (NGC 7099), with uncertainties between 0.5 and 5 km s-1. In 47 Tuc and NGC 6397, the dispersion profiles at first increase with decreasing radii but then flatten in the central 0′.4. This is the same behavior seen in our previously published profile for M15. The measured stellar velocities show that 47 Tuc is rotating, with a projected rotation axis that is aligned with the isophotal minor axis. We also find a similar alignment for the rotation that we previously measured in M15. A map of the average velocity in the central regions derived from the integrated light shows rotation for NGC 6397 and 47 Tuc. For 47 Tuc, NGC 6397, and M15, the amplitude of the projected rotation measured at a radius of 0′.6 using the individual stellar velocities is equal to, or smaller than, that measured at a radius of 0′.2 using the integrated light. This is not consistent with the solid-body rotation usually assumed for the inner regions. To study further the form of the projected rotation we have used two-dimensional spline smoothing to derive a mean velocity map for 47 Tuc using the individual stellar velocities. This map shows that the projected rotation velocity reaches a plateau at a radius of 3′ and that the radial dependence of the projected rotation velocity deviates significantly from solid body beyond 2′. We have repeat measurements of the two "high-velocity" stars of Meylan, Dubath, and Mayor. However, we detect more stars with similar large offsets from the cluster mean velocity. The number of stars that we measure with large velocity offsets is consistent with a normal distribution, so that there is no need to invoke a special creation mechanism for these stars.

Original languageEnglish (US)
Pages (from-to)1699-1711
Number of pages13
JournalAstronomical Journal
Issue number4
StatePublished - Oct 1995

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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