NGC 6604

NGC 6604 is a young^[6] open cluster of stars in the equatorial constellation of Serpens, positioned about 1.5° north of the Eagle Nebula (NGC 6611).^[7] The cluster was discovered by William Herschel on July 15, 1784.^[8] It is located at a distance of 4,580^[2] light years from the Sun, about 210 ly (65 pc) above the galactic plane.^[7] NGC 6604 forms the densest part of the Ser OB2 association of co-moving stars.^[9]

NGC 6604
NGC 6604 and its surroundings taken by the Wide Field Imager attached to the 2.2-metre MPG/ESO telescope at the La Silla Observatory in Chile
Observation data (J2000 epoch)
Right ascension	18h 18m 03.0s[1]
Declination	−12° 14′ 30″[1]
Distance	4,580 ly (1,403 pc)[2]
Apparent magnitude (V)	6.5[3]
Physical characteristics
Estimated age	6.5 Myr[1]
Other designations	NGC 6604, Cr 373, MM 23, OCl 56, C 1815-122, CTB 50, NRL 17, [KPR2004b] 439, Cl Mrk 39, LMH 24, OCISM 11[4]
Associations
Constellation	Serpens[5]
See also: Open cluster, List of open clusters

This cluster is fairly compact with a Trumpler class of I3p,^[6] and is still undergoing star formation.^[10][7] It lies at the heart of an H II region with the identifier S54, and the two are most likely linked.^[6] The cluster has an estimated age of 6.5^[1] million years and contains several massive stars of the OB type.^[6] One of these is the high mass triple star system HD 167971, which includes the over-contact eclipsing binary MY Ser. It is one of the most luminous stars in the galaxy.^[10] HD 168112 is another colliding-wind binary in the cluster; both systems are over-luminous in their X-ray emission.^[11]