NGC 2506 (also known as Caldwell 54) is a mildly-elongated[6]open cluster of stars in the
equatorialconstellation of
Monoceros, located at a distance of 12.7
kly[2] from the Sun near the Galactic anti-center.[4] It was discovered by
William Herschel in 1791.[7] The cluster lies around 10,000 ly from the
Galactic Center and about 1,600 ly above the
Galactic plane.[4] It is of intermediate age,[2] estimated at around two billion years.[2] The cluster has an angular radius of 12′ and a core radius of 4.8′.[8]
At least 94 probable members have been identified within the field of NGC 2506 based upon their
radial velocities. Compared to the Sun, the cluster is moderately
metal-poor with an iron abundance of [Fe/H] = –0.3
dex.[9] It shows indications of mass segregation, with the lower mass members being more likely to be in the outer parts of the cluster. This is the result of exchange of kinetic energy during encounters between the members.[10] Twelve
blue straggler stars have been located in the cluster, with three of them showing short-period oscillation. Fourteen
Gamma Doradus variables have been found, as well as two
detachedeclipsing binaries,[6] and three
Delta Scuti stars.[11]
^
abcdeRangwal, Geeta; et al. (November 2019). "Astrometric and photometric study of NGC 6067, NGC 2506, and IC 4651 open clusters based on wide-field ground and Gaia DR2 data". Monthly Notices of the Royal Astronomical Society. 490 (1): 1383–1396.
arXiv:1909.08810.
Bibcode:
2019MNRAS.490.1383R.
doi:
10.1093/mnras/stz2642.
^Lee, S. H.; et al. (June 2013). "Deep and wide photometry of two open clusters NGC 1245 and NGC 2506: dynamical evolution and halo". Monthly Notices of the Royal Astronomical Society. 432 (2): 1672–1679.
arXiv:1304.1967.
Bibcode:
2013MNRAS.432.1672L.
doi:
10.1093/mnras/stt588.
^Kim, S. -L.; et al. (March 2001). "Search for Variable Stars in Two Old Open Clusters: NGC2506 and NGC2420". Acta Astronomica. 51: 49–63.
Bibcode:
2001AcA....51...49K.