\cent: the jumbo galactic globular cluster

Session 58 -- The Galaxy
Display presentation, Thursday, 2, 1994, 9:20-6:30

[58.16] \cent: the jumbo galactic globular cluster

\def\arcm {$^{\prime}$} \def\cent {$\omega$\thinspace Centauri} \def\kms {km\thinspace s$^{-1}$} \def\Mtot {$M_{tot}$} \def\mlv {$M/L_V$} \def\milm {${ {10^6 M_{\odot}}}$} \def\pmm {$\pm$} \def\sigp {$\sigma_p$} \def\sigpo {$\sigma_p$(0)} G. Meylan (ESO), M. Mayor (Geneva), P. Dubath (ESO)

The mean radial velocities obtained with CORAVEL for 469 individual stars in the galactic globular cluster \cent\ $\equiv$ NGC~5139 are used to derive the velocity dispersion profile. It decreases significantly from the center outwards: the 16 innermost stars, located within 1\arcm\ from the center, have a velocity dispersion \sigp\ = 21.9 \pmm\ 3.9 \kms, when the 16 outermost stars, located between 19.2\arcm\ and 22.4\arcm\ from the center, have a velocity dispersion \sigp\ = 5.1 \pmm\ 1.6 \kms. The inner value of about \sigpo\ = 22 \kms\ is the largest velocity dispersion value obtained in the core of any galactic globular cluster. A simultaneous fit of these radial velocities and of the surface brigthness profile to a multimass King-Michie dynamical model provides mean estimates of the total mass equal to \Mtot\ = 5.1 \milm, with a corresponding mean mass-to-light ratio \mlv\ = 4.1. The present results emphasize the fact that \cent\ is not only the brightest but also, by far, the most massive galactic globular cluster.

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