Astron. Astrophys. 356, 118-126 (2000)

5. Conclusions

Spectroscopic observations have been made for the young open cluster NGC 6913. Spectra of 100 stars having membership probability greater than 50% are obtained and classified. Reddening is estimated on the basis of spectral classification. The variable extinction across NGC 6913 is analyzed and discussed. The results of our study can be summarized as follows.

1. From the spectroscopic observations, it is found that the spectral type distribution in our sample covers from O7 to K3. There are only 2 O-type stars in this OB association. 40 and 33 percent of the total stars are B and A type stars respectively, and the F, G, K stars amount to 25 percent.

2. Many of the values of interstellar reddening from spectral classification are quite different from those taken from photometry (especially for early B and F type stars), in which the largest discrepancy is 1.48 mag.. This further demonstrates that correct spectral classification is extremely important for the study of reddening and extinction of stars. Hence, it is necessary to make spectroscopic observations first before studying interstellar extinction of young open cluster. Photometry only is insufficient.

3. The extreme variation of extinction across NGC 6913 is shown. The distribution of extinction in the region is correlated with the effective temperature of the stars in the case of the stars earlier than F8. This could mean that the more luminous new formed stars have a higher mass loss rate.

4. It is found that extinction in the cluster center is relatively homogeneous, but very large. In this cluster, the north and south have the largest extinction. The east and west seem to be low reddening regions.

5. A mean distance modulus of the cluster of mag. is derived, which corresponds to a distance of 1.08 kpc.

6. Based on a reddening method, a total amount of of the stars with membership probability greater than 50% can be derived to be probable "non-members" of the cluster.

7. Some interesting objects are found in this study. Further observations for these stars will be made in the future.

© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000
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