NGC 2506

NGC 2506 (also known as Caldwell 54) is a mildly-elongated^[6] open cluster of stars in the equatorial constellation 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]

NGC 2506
A composite image of NGC 2506 from multiple astronomical surveys
Observation data (J2000 epoch)
Right ascension	08h 00m 01.0s[1]
Declination	−10° 46′ 12″[1]
Distance	12.7 ± 1.4 kly (3.88 ± 0.42 kpc)[2]
Apparent magnitude (V)	7.6[3]
Apparent dimensions (V)	12′[4]
Physical characteristics
Radius	18.5 ly[4]
Estimated age	2.09±0.14 Gyr[2]
Other designations	Caldwell 54, Cr 170, Mel 80[5]
Associations
Constellation	Monoceros
See also: Open cluster, List of open clusters

Map showing the location of NGC 2506

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 detached eclipsing binaries,^[6] and three Delta Scuti stars.^[11]