Radial Variation of Optical and Near-Infrared Colours in Luminous   Early-Type Galaxies in ABELL 2199
  We performed K band surface photometry for luminous early-type galaxies in a nearby rich cluster ABELL 2199. Combining it with B and R band surface photometry, radial variations of B-R and R-K colours in the galaxies were investigated. It is found that the inner regions of the galaxies are redder in both of B-R and R-K colours. Comparing the radial variations of both of the colours with predictions of Simple Stellar Population (SSP) models for a range of ages and metallicities, it is suggested that the cluster ellipticals have negative metallicity gradients but their age gradients are consistent with zero, although our sample is small; the typical metallicity gradient is estimated to be -0.16+- 0.09 in dlogZ/dlogr, while the age gradient is estimated to be -0.10 +- 0.14 in dlog(age)/dlogr. Considering that similar results have also been derived in the other recent studies using samples of ellipticals in the Coma cluster and less dense environments, it seems that there is no strong dependence on galaxy environment in radial gradient of stellar population in elliptical galaxy. 
Naoyuki Tamura (1) and Kouji Ohta (2) ((1)University of Durham,   (2)Kyoto University)