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


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Spectral classification and reddening in the young open cluster NGC 6913

J.-J. Wang 1,2,3 and J.-Y. Hu 1

1 Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100012, P.R. China
2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, P.R. China
3 Beijing Astrophysics Center, jointly operated by Chinese Academy of Sciences and Beijing University, Beijing 100871, P.R. China

Received 9 March 1999 / Accepted 11 January 2000

Abstract

Spectroscopic observations have been made for the young open cluster NGC 6913. In total, the spectra of 100 stars of the cluster, having membership probability greater than 50%, have been obtained and classified. Reddening is estimated on the basis of spectral classification. The variable extinction across NGC 6913 is analyzed and discussed. 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.

An extreme variation of extinction is found across the young open cluster NGC 6913. The distribution of extinction in the region is correlated with the effective temperature of the stars for stars earlier than F8. It is found that extinction in the cluster center is relatively homogeneous, but very large. The north and south of this cluster have the largest extinction. The eastern and western parts seem to be low reddening regions. A mean distance modulus of [FORMULA] mag. is derived for the cluster, which corresponds to a distance of 1.08 kpc.

A large part of the values of interstellar reddening of the stars in NGC 6913 from spectral classification are quite different from those taken from photometry (especially for early B and F type stars); the largest discrepancy amounts to 1.48 mag.. Depending on a reddening method, a total amount of [FORMULA] of the stars with membership probability greater than 50% can be evaluated to be probable "non-members" of the cluster.

In addition, some interesting objects are found in this study. Further observations for these stars will be made in the future.

Key words: stars: fundamental parameters – ISM: dust, extinction – Galaxy: open clusters and associations: general

Send offprint requests to: J.-J. Wang (wangjj@class1.bao.ac.cn)

© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000

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