Studies of dynamical properties of globular clusters. I - Kinematic parameters and binary frequency in 47 Tucanae

Details Studies of dynamical properties of globular clusters. I - Kinematic parameters and binary frequency in 47 Tucanae Studies of dynamical properties of globular clusters. I - Kinematic parameters and binary frequency in 47 Tucanae

May 1984

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984a%26a...134..118m&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 134, no. 1, May 1984, p. 118-122.

Astronomy and Astrophysics

Astrophysics

71

Globular Clusters, Radial Velocity, Stellar Motions, Binary Stars, Rotation

Scientific paper

This paper analyses the results of accurate photoelectric radial velocity observations of 169 stars in 47 Tucanae, situated between 2 and 30 core radii from the cluster centre. The observations are published separately (Mayor et al., 1983). Radial velocity variations of 2-5 km s-1 in stars brighter than mv= 12 (Mv<-1.2) are found to be due to pulsational instability onthe upper part of the giant branch. Among the stars fainter than mv = 12, no spectroscopic binaries were found either, indicating a lower binary frequency and/or different distribution of orbital parameters than in field stars in the solar neighbourhood. This result concerns only the external region of the cluster (r> 5rc). The average radial velocity of 47 Tuc is -19±1 km s-1. In contrast to earlier results, no spectral-type dependence of the average radial velocities can be found. The differential rotation of the cluster has been detected and analysed. For the maximum rotational velocity, the phase is θ =28° ±20° in good agreement with the direction of the major axis of the projected stellar distribution. Themaximum observed rotational velocity, Vmax≃ 7kms -1, reached inside 6 core radii from the cluster centre. The ratio of Vmax to the velocity dispersion close to the cluster centre, ,σ0, Vmax/σ0> 0.7, ± 0.4 seems rather high for a cluster with an ellipticity of 0.1.

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