Blue Horizontal Branch Stars in NGC 6522 And Baade's Window
Abstract
We present color-magnitude diagrams in BVI (Cousins) of the globular cluster NGC 6522 in Baade's Window. Our photometry, which extends to V approximately equals 19, shows that NGC 6522 has an extended blue horizontal branch (BHB), typical of clusters of moderate metallicity close to the galactic center. We derive (Fe/H) = -1.6 +/- 0.2, E(B-V)zero = 0.52 +/- 0.05 for the cluster from comparison to the giant branches of other globulars and from the level of the cluster's horizontal branch. We identify a region in the color-magnitude diagrams which is populated mainly by BHB stars, and show that most of these are spatially concentrated around the cluster and so are not members of the bulge; the spatial density of bulge BHB stars is 0.4 arcmin-2. If the bulge has the same (1750 A--V) color as the bulge of M31, then about 20% the light at 1750 A is from BHB stars.
- Publication:
-
The Astronomical Journal
- Pub Date:
- May 1994
- DOI:
- 10.1086/116986
- Bibcode:
- 1994AJ....107.1786T
- Keywords:
-
- Abundance;
- Astronomical Photometry;
- Blue Stars;
- Color-Magnitude Diagram;
- Galactic Bulge;
- Globular Clusters;
- Horizontal Branch Stars;
- Metallicity;
- Spatial Distribution;
- Calibrating;
- Charge Coupled Devices;
- Data Reduction;
- High Resolution;
- Optical Filters;
- Spatial Resolution;
- Telescopes;
- Astronomy;
- GLOBULAR CLUSTERS: INDIVIDUAL: NGC 6522;
- STARS: HORIZONTAL-BRANCH