Padova University |
Physics & Astronomy Dep. |
Asiago Observatory |
Padova Observatory |
Half size CM-diagram preview |
NGC 6121 Photometric Data (gzipped) Globular Cluster parameters Observed fields preview |
NGC 6121 (M 4)This cluster is the closest GGC, located approximately at ∼2.2 kpc from the Sun, though, due to the large reddening caused by the nebulosity in Scorpio-Ophiuchus, it has an apparent visual distance modulus larger than NGC 6397. The reddening is differential, though (as in the case of NGC 4372) it is homogeneously distributed in space. The mean sequences of the CMD can be improved using an appropriate second order polynomial fit to the reddening distribution, at least on the two fields shown. The stars from the southern field have been plotted as darker dots; they are located on the redder (more reddened) part of the CMD. The two most recent CMD of M 4 are in Ibata et al. (1999) and Pulone et al. (1999), who present HST studies of the faint part of the MS and of the WD sequence. Other recent CMDs from the RGB tip to below the MSTO are in Alcaino et al. (1997), who presented an U, B, V, I CCD photometry, and Kanatas et al. (1995), who obtained a composite (B, V) CMD from V∼12 to V∼25. |