Cepheids in Galactic Clusters. VII. S Nor and NGC 6087.
Abstract
Photometric observations of the galactic cluster NGC 6087 and the associated 9.8-day cepheid S Nor are presented. A distance of 760 pc (m-M = 9.4 mag.) is derived, implying an average absolute magni tude Mv = -3.7 for S Nor. The color excess is found to be constant across the cluster and has a value EB- V = 0.22 mag., which gives the cepheid an average intrinsic color index of (B - V) = 0.75 mag. The age of the cluster is found to be about 1-2 X 10 years. Evidence is presented that the period of the cepheid may be increasing at a rate of about 5 seconds per year, and this is discussed as a possible evolutionary effect.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 1961
- DOI:
- 10.1086/147003
- Bibcode:
- 1961ApJ...133...64F