Credit: Jim Fordice
Astronomical and Imaging Data
| RA: | 04h 24m 44.5s |
| DEC: | -21° 11′ 13.0″ |
| MAG: | 14.70 |
| Diameter: | 1.0′ |
| Const: | Eri |
| OTA | Planewave CDK24 |
| Focal Length | 3962mm |
| Camera | QHY 600M |
| Site | Río Hurtado, Chile |
| Sky Quality | Bortle 1 |
Useful Informations
The stellar system referred to simply as “Eridanus” in the context of globular clusters is a low−mass Galactic globular cluster residing in the outer halo of the Milky Way. It is considered a particularly important object for studying the properties of low-mass stellar clusters.
Key Characteristics
Location and Type
- Type: A low−mass globular cluster in the Milky Way’s stellar halo.
- Distance and Classification: Eridanus is considered an outer halo cluster, often studied alongside other remote clusters like Palomar 3, Palomar 4, and AM 1.
Age and Morphology
- Age: Eridanus is classified as a “second-parameter” cluster, meaning its stellar characteristics are not solely explained by its metallicity. Studies suggest it is significantly younger than the “classic” inner halo globular clusters (like M3 and M15), potentially by about 1.5−2 Gyr.
- Horizontal Branch (HB) Anomaly: It exhibits a red horizontal−branch morphology despite having a low-to-intermediate metallicity, which is the defining characteristic of the “second-parameter” problem in globular cluster science.
Chemical Composition
- Metallicity: Eridanus has a low−to−intermediate metallicity, with its iron abundance, [Fe/H], generally placing it near or between the values of clusters like M3 and M5.
- Multiple Populations: Significant research has been dedicated to Eridanus due to its low mass to test the hypothesis that all globular clusters harbor Multiple Populations (MPs). Observational evidence, specifically a significant dispersion in the initial surface abundance of nitrogen and carbon in its giant stars, confirms the existence of Multiple Populations in this cluster, demonstrating that the mass threshold for MP formation is quite low.