Astronomical and Imaging Data

Useful Informations

Ruprecht 106 (RUP 106) is a relatively metal-poor and dynamically young Galactic globular cluster, notable for its potential to host a simple stellar population.

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Key Physical Characteristics

RUP 106 is a star cluster located in the outer Galactic halo.

• Location and Distance: It is situated at an approximate distance of 69,100 light-years (or 21.2 kpc) from the Sun and about 60.3 kly (18.5 kpc) from the Galactic Center. Its current radial velocity is about -44 km/s, indicating it is currently moving towards the Sun.
• Metallicity: The cluster is categorized as metal-poor, with a spectroscopic iron abundance generally determined around [Fe/H] -1.5 to -1.7 (relative to the Sun). This is typical for halo globular clusters.
• Age: RUP 106 is considered to be one of the younger Galactic globular clusters, with some photometric studies suggesting it might be several billion years younger than the oldest clusters of similar metallicity. It is often grouped with other potentially “young” outer halo globular clusters like Palomar 12.
• Dynamical State: Observations suggest RUP 106 is dynamically young. This conclusion is based on the analysis of star populations like Blue Straggler Stars and the cluster’s mass function, which indicate that the process of dynamical friction, which segregates massive stars toward the cluster center, is only beginning.

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Unique Scientific Significance

RUP 106 holds a special place in stellar astrophysics due to its potential status as a true single stellar population cluster.

• Single Population Candidate: Almost all observed globular clusters show evidence of multiple stellar populations (MPs)—meaning they contain at least two groups of stars with distinct chemical compositions (particularly light elements like Oxygen, Sodium, and Helium). RUP 106 is one of the few clusters where extensive studies, including high-precision photometry and spectroscopy of its brightest stars, have so far failed to find robust evidence for the characteristic light-element spreads or the split in its stellar sequences typical of multiple populations. This lack of a measurable spread in key light elements challenges the current understanding of globular cluster formation and the universality of the multiple population phenomenon.
• Blue Straggler Stars: The cluster hosts a significant, centrally concentrated population of Blue Straggler Stars, which are stars in the color-magnitude diagram that appear hotter and brighter than the main sequence turnoff, suggesting they are either stellar mergers or members of mass-transfer binaries that have undergone rejuvenation.

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