Astronomical and Imaging Data

Useful Informations

NGC 6293 is an ancient and relatively metal-poor globular cluster located in the southern constellation of Ophiuchus. It is a significant object for galactic studies due to its classification as an inner halo cluster, meaning it orbits close to the Milky Way’s central bulge.

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Astrophysical Characteristics

• Location and Distance: This cluster is estimated to be approximately 9.5 kiloparsecs (∼30,000 light-years) from the Sun. Its proximity to the Galactic Center is noteworthy, with a calculated Galactocentric distance of around 1.9 kiloparsecs. This makes it one of the globular clusters embedded in the inner regions of the Galaxy.
• Metallicity and Age: NGC 6293 is definitively classified as metal-poor, with an iron abundance [Fe/H] ≈−1.99 (less than 2% of the Sun’s metal content). This very low metallicity indicates that the cluster formed very early in the universe, and photometric studies of its stellar populations, particularly its blue horizontal branch stars, confirm that it is an extremely old cluster, with an age comparable to the oldest known globular clusters, such as M92.
• Kinematics: The cluster’s heliocentric radial velocity is a moderately high −143.7 kilometers per second, suggesting that it is currently moving towards the Sun. This velocity is part of its overall orbit within the Galactic halo.

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Structure and Appearance

• Concentration: NGC 6293 is classified as having a relatively high stellar concentration, with a Shapley–Sawyer Concentration Class of IV. This suggests a tightly packed core, although it is not considered “core-collapsed.” The cluster’s appearance is often described as bright, large, and showing a noticeable increase in brightness toward its center.
• Reddening and Stellar Content: The cluster’s location near the plane of the Galaxy means its light is attenuated and reddened by intervening interstellar dust. Studies show a significant and even slightly differential reddening across the face of the cluster. Observations, particularly those from the Hubble Space Telescope, have also confirmed the presence of Blue Straggler Stars in the cluster’s central regions, which are anomalous blue stars often formed through stellar collisions or mass transfer in crowded stellar environments. The presence of the dark nebula Barnard 59 near the cluster reinforces the fact that its line of sight passes through regions of dense, obscuring gas.

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