2 Data

The online available database at http://obswww.unige.ch/webda/ by Mermilliod (1995) provides an excellent compilation of the data on open clusters. We selected a range of $120^{\circ}<l<150^{\circ}$ to study the intra-cluster extinction in open clusters. The online database lists 103 clusters in this longitude range. The parameters, such as distance, E(B-V), age etc., are available for only 54 clusters. Seventeen clusters in this direction are quite young (log age < 7.5) and are suitable to study the behaviour of intra-cluster ISM. UBV CCD photometry for nine young clusters of the above sample is given by Phelps & Janes (1994). A casual look at the (U-B)/(B-V)two-colour diagrams (TCDs) given by Phelps & Janes (1994, hereafter PJ94) indicates that the photometric data of 3 clusters, namely Be 62, NGC 637 and NGC 663, do not satisfy the main-sequence (MS) curve, where apparent UVexcess can be seen for stars having spectral type later than A. PJ1994 concluded that this may be due to UV excess of pre-main-sequence (PMS) stars and this part of the (U-B)/(B-V) TCD is not suitable for reddening estimation. We will discuss (U-B)/(B-V) TCDs in ensuing sections. The present analysis has been carried out using photometric data of 14 clusters and details are given Table 1.