Credit: Jim Fordice
Astronomical and Imaging Data
| RA: | 17h 14m 32.25s |
| DEC: | -29° 27′ 43.3″ |
| MAG: | 8.22 |
| Diameter: | 8.0′ |
| Const: | Oph |
| OTA | Planewave CDK24 |
| Focal Length | 3962mm |
| Camera | QHY 600M |
| Site | El Sauce Observatory,Río Hurtado, Chile |
| Sky Quality | Bortle 1 |
Useful Informations
NGC 6304 is a highly significant globular cluster located in the constellation Ophiuchus, distinguished primarily by its proximity to the Galactic Center and its high metal content. It serves as a crucial reference point for studies of the Milky Way’s bulge population.
Key Physical Characteristics
- Location and Distance: NGC 6304 is a member of the Galactic Bulge globular cluster system. It lies approximately 5.9 kiloparsecs from the Sun. Critically, its location translates to a Galactocentric distance of around 2.3 kiloparsecs, firmly placing it within the central, dense volume of the Milky Way Galaxy.
- Metallicity and Stellar Population: Unlike the extremely metal-poor clusters found in the outer halo, NGC 6304 is classified as metal-rich, with an iron abundance [Fe/H] approx -0.45. This places it among the most chemically enriched globular clusters, comparable to the stellar content of the Galactic Bulge itself. Its Color-Magnitude Diagram (CMD) shows a Red Giant Branch (RGB) and a Red Horizontal Branch (RHB) morphology, which is characteristic of high-metallicity clusters. The cluster is estimated to be very old, with an age of approximately 12.3 billion years.
- Kinematics: The cluster’s heliocentric radial velocity is low, at roughly -26.0 kilometers per second (or similar low negative values depending on the source), indicating that it is currently approaching the Sun at a relatively slow pace.
Appearance and Dynamical State
- Concentration: NGC 6304 has a moderate to high degree of stellar concentration, classified with a Shapley–Sawyer Concentration Class of VI. Its high stellar density and proximity to the dust-rich Galactic plane result in it being highly affected by interstellar reddening, with an extinction value, E(B-V), of about 0.5 magnitudes.
- Observational Properties: Visually, it is a relatively faint object with an integrated visual magnitude of 8.22 and a small apparent size of about 8 arc minutes. Its small apparent size and high reddening complicate ground-based optical studies, which is why near-infrared (NIR) observations are often used to penetrate the intervening dust and better resolve its stellar populations.
- Exotic Objects: Like many dense globular clusters, NGC 6304 is a site of stellar dynamics and high-energy phenomena. Studies have targeted the cluster to search for and characterize X-ray sources, including quiescent low-mass X-ray binaries (qLMXBs), which are remnants of highly evolved stellar systems.