Fabry-Perot Velocities For Globular Cluster Stars: M15, M3, and M4

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Session 104 -- Globilar Clusters
Display presentation, Thursday, 12, 1995, 9:20am - 6:30pm

[104.12] Fabry-Perot Velocities For Globular Cluster Stars: M15, M3, and M4

Karl Gebhardt (Univ. of Michigan), Carlton Pryor and T. B. Williams (Rutgers University), James E. Hesser (DAO/HIA/NRC)

\def\kms{km~s$^{-1}$} \def\arcsec{\ifmmode {'' } \else $'' $\fi}

We are engaged in a continuing project that uses an imaging Fabry-Perot spectrophotometer on the 3.6-m CFHT and the 4~m and 1.5~m telescopes at CTIO to measure both absorption-line integrated-light velocity maps for globular clusters and velocities for large samples of cluster stars (Gebhardt, K., Pryor, C., Williams, T.B., \& Hesser, J.E. 1994, AJ, 107, 2067; Gebhardt, et al. 1994, submitted). Our goals are to study such kinematic properties as rotation and the number of high-velocity stars, and to use the velocity dispersion profiles to determine non-parametric mass profiles using the technique of Gebhardt \& Fischer (1995, January AJ). Here we present radial velocities with accuracies of 1--5 \kms\ for about 600 stars in the cusp cluster M15, 400 stars in the centrally-concentrated cluster M3, and 1900 stars in the nearby cluster M4.

The M15 dataset contains three times more stellar velocities throughout the whole cluster and five times more in the inner 10\arcsec\ than the previous study of Gebhardt \& Fischer. This larger sample continues to show no evidence for a central cusp in the velocity dispersion profile. The M4 data constitute one of the largest radial velocity samples yet obtained for a globular cluster. The stars in the sample range from magnitude V=10 to V=18.5. V=18.5 is 2.5 magnitudes below the main-sequence turn-off, so these data are valuable first-epoch information for determining the main-sequence binary fraction. We present two-dimensional velocity maps, velocity dispersion profiles, and radial mass profiles for the three clusters.

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