Mass Segregation and Tidal Tails of the Globular Cluster NGC 7492

Abstract

We present a wide-field CCD photometric study of the Galactic globular cluster NGC 7492. The derived VR color-magnitude diagram (CMD) extends down to about 3.5 mag below the cluster main- sequence turnoff. The field covers 420; 420, about 3 times larger than the known tidal radius of this cluster. The sample of cluster member candidates obtained by the CMD-mask process has been used to construct luminosity (LFs) and mass functions (MFs) and a surface density map. NGC 7492 has a very flat MF with very little variation in the slope with distance from the cluster center. However, there is a clear evidence for an increase of the MF slope from inner to outer regions, indicating mass segregation of the cluster. The surface density map of NGC 7492 shows extensions toward the Galactic anticenter ( northeast) and northwest from the cluster center. A comparison of the LF for stars in the tails with that for stars within the tidal radius suggests that the extensions shown in the surface density map could be a real feature. The overall shape of NGC 7492 is significantly flattened. If the flattened shape of the NGC 7492 is caused by its rotation, the Galactic tidal field must have been an important influence, since the initial rotation would have been almost completely removed by dynamical relaxation.