SCYON Abstract

Received on July 5 2001

Non-uniform extinction in young open star clusters

AuthorsR. K. S. Yadav1, Ram Sagar1, 2
Affiliation1State Observatory, Manora Peak Nainita, 263129 India,
2Indian Institute of Astrophysics, Bangalore 560034, India
Accepted byMNRAS
Links NGC 663 | NGC 869 | NGC 884 | NGC 1502 | NGC 1893 | NGC 2244 | NGC 6611 | Tr 14 | Tr 15 | Tr 16 | Tr 37 | Be 86 | Cr 228 |


The extinction law and the variation of colour excess with position, luminosity as well as 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 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 due to the presence of gas and dust, decreases systematically with the age of clusters indicating that matter is used either in star formation or blown away by hot stars or both. There is no uniformity in the variation of E(B-V) with either 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. The members of these clusters at lambda > lambdaR show larger values of colour excess ratios than the normal ones. The value of E(U-V) / E(B-V) for most of the cluster members is close to the normal interstellar value of 1.73. However, the colour excess ratios with E(B-V) at lambda > lambdaJ are smaller than the normal value for NGC 663, NGC 869, NGC 884 and NGC 1502 while they are larger for NGC 6611, Coll 228, Tr 16 and Tr 14. Thus there is no uniformity in the relationship of extinction properties amongst the clusters under study.