NGC 6553
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| NGC 6553 | |
|---|---|
 The globular cluster NGC 6553 imaged by the Hubble Space Telescope | |
| Observation data (J2000 epoch) | |
| Class | V |
| Constellation | Sagittarius |
| Right ascension | 18h 09m 15.68s[1] |
| Declination | −25° 54′ 27.9″[1] |
| Distance | 19.6 kly (6.01 kpc)[1] |
| Apparent magnitude (V) | 8.06[2] |
| Physical characteristics | |
| Radius | 4.1' x 4.1'[2] |
| Metallicity | [Fe/H] = −0.18[3] dex |
| Estimated age | 11 ± 0.5 Gyr[4] |
| Other designations | GCl 88, C 1806-259[1] |
NGC 6553 is a globular cluster in the constellation Sagittarius. NGC 6553 has an apparent magnitude of about 8th magnitude with an apparent diameter of 8.2 arcminutes.[2] Its Shapley–Sawyer Concentration Class is XI,[2] meaning the star concentration is very loose even at the center; it has stars of magnitude 20 and dimmer. It is located just over a degree southeast of Messier 8, the Lagoon Nebula.
Unlike common globular clusters, NGC 6553 is relatively metal-rich, and there is evidence of at least two periods of star formation.[5] Due to a complex star-forming record, the stars in the cluster are differing in composition, most notably in concentrations of sodium and aluminium.[6]
NGC 6553 is very similar in composition to NGC 6528, suggesting an origin in a similar environment.[7]
