Credit: Jim Fordice
Astronomical and Imaging Data
| RA: | 18h 01m 38.80s |
| DEC: | -26° 50′ 23.0″ |
| MAG: | 16.0 |
| Diameter: | 0.2′ |
| Const: | Sgr |
| OTA | Planewave CDK24 |
| Focal Length | 3962mm |
| Camera | QHY 600M |
| Site | Río Hurtado, Chile |
| Sky Quality | Bortle 1 |
Useful Informations
Terzan 9 is a globular cluster located in the inner region of the Milky Way galaxy, making it a critical object for studying the early formation and chemical evolution of the Galactic Bulge.
Galactic Location and Extinction
Terzan 9 is situated in the direction of the constellation Sagittarius, lying very close to the Galactic Center.
- Distance and Position: It is estimated to be approximately 23,000 to 25,000 light years from the Sun. Its position means it is one of the clusters belonging to the Galactic Bulge or the innermost halo. It has a very low Galactic latitude, meaning it lies very near the plane of the Milky Way disc.
- High Extinction: Due to its location, the cluster is heavily obscured by the dense interstellar dust and gas of the Galactic Plane. This phenomenon, known as extinction, severely dims and reddens the cluster’s light, especially at visible wavelengths. This strong extinction is the primary challenge for its study, requiring the use of infrared observations from telescopes like the Hubble Space Telescope to effectively penetrate the dust and resolve its individual stars. The cluster’s significant dimming in optical light is characteristic of the Terzan clusters, which were discovered relatively late (in the 1960s) for this reason.
Stellar Population and Metallicity
Terzan 9 is a dense, spheroidal aggregate of many thousands of stars that are gravitationally bound.
- Age and Metallicity: Like most globular clusters, Terzan 9 is an ancient object, one of the oldest stellar systems in the galaxy. Its stellar population is consistently classified as metal-poor, with a low abundance of heavy elements. This is typical of the oldest stellar populations in the Milky Way, which formed when the raw material for stars had not yet been enriched by the explosions of early massive stars. Published measurements of its iron abundance ([Fe/H]) generally place it at a value around -0.5 to -0.6, confirming its metal-poor nature.
- Horizontal Branch: Studies of its color magnitude diagram have identified it as a cluster with a blue horizontal branch morphology, which is often correlated with the cluster’s old age and low metallicity. The high stellar density in its core promotes close encounters, which can lead to the formation of binary stars and other exotic objects.