Non-uniform extinction in young open star clusters

Abstract

The extinction law and the variation of colour excess with position, luminosity and spectral

class in young open star clusters NGC 663, NGC 869, NGC 884, NGC 1502, NGC 1893,

NGC 2244, NGC 2264, NGC 6611, Tr 14, Tr 15, Tr 16, Coll 228, Tr 37 and Be 86 have been

studied. The difference in the minimum and maximum values of E(B - V) of cluster

members has been considered as a measure of the presence of non-uniform gas and dust

inside the clusters. Its value ranges from 0.22 to 1.03 mag in the clusters under study, which

indicates that non-uniform extinction is present in all the clusters. It has been noticed for the

first time in NGC 1502 and Tr 37. It is also found that the differential colour excess in open

clusters, which may be caused by the presence of gas and dust, decreases systematically with

the age of clusters, indicating that matter is either used in star formation or blown away by hot

stars or both. There is no uniformity in the variation of E(B - V) with position or spectral

class or luminosity. Except in Tr 14, all clusters show a random spatial distribution of

E(B - V), indicating a random distribution of gas and dust inside the clusters. The E(B – V) value correlates with both luminosity and spectral class only in the case of Coll 228, Tr 16 and

Be 86.