Credit: Jim Fordice
Astronomical and Imaging Data
| RA: | 17h 04m 28.51s |
| DEC: | -24° 45′ 53.5″ |
| MAG: | 8.83 |
| Diameter: | 6.1′ |
| Const: | Oph |
| OTA | Planewave CDK24 |
| Focal Length | 3962mm |
| Camera | QHY 600M |
| Site | El Sauce Observatory,Río Hurtado, Chile |
| Sky Quality | Bortle 1 |
Useful Informations
The globular cluster NGC 6284 is an ancient and relatively metal-poor stellar system situated in the constellation Ophiuchus. It represents a dynamically mature object within the Milky Way’s halo, characterized by a highly collapsed core.
Key Physical Parameters
- Age and Metallicity: NGC 6284 is confirmed to be an extremely old system, with a precise age estimate of approximately 13.3 billion years. Its stellar population is metal-poor, with a metallicity ratio [Fe/H] of around -1.36 (with some estimates placing it closer to -1.26).
- Distance and Location: The cluster is located a true distance of about 43,000 light years from the Sun. Its position far from the Galactic plane and center places it firmly within the outer stellar halo of the Milky Way.
- Apparent Properties: It is moderately bright for a globular cluster, with an apparent visual magnitude of 8.83, and spans an angular diameter of about 6.1 arc minutes in the sky.
- Extinction: Observations confirm that the cluster is subject to a significant amount of interstellar reddening, with an average color excess E(B-V) of about 0.32.
Structure and Dynamical State
- Core Collapse Morphology: The most significant structural finding is that NGC 6284 is a post-core collapse (PCC) cluster. Analysis of its stellar density profile shows the presence of a steep central cusp, which is the definitive signature of a core that has undergone a catastrophic gravitational collapse.
- Concentration: Its high central density corresponds to a high concentration class, typically classified as IX on the Shapley–Sawyer scale, which indicates a very compact structure.
- Color-Magnitude Diagram (CMD): Deep photometric studies using the Hubble Space Telescope have produced a high-quality CMD that clearly extends below the main-sequence turn-off. This diagram shows a narrow Red Giant Branch (RGB), allowing for the clear identification of the RGB bump—a feature used for precise stellar evolution calibration.
Kinematics
The cluster has a measured heliocentric radial velocity of about +29.0 kilometers per second (moving away from the Sun), with relatively low internal velocity dispersion, characteristic of a tightly bound stellar system. This kinematical data, in conjunction with its distance and metallicity, is used to model its orbit and understand its contribution to the overall structure of the Galactic halo.