NGC 6539

NGC 6539
Globular cluster NGC 6539
Observation data (J2000 epoch)
ClassX:[1]
ConstellationSerpens
Right ascension18h 04m 49.74s[2]
Declination–07° 35′ 09.1″[2]
Distance26.63 kly (8.165 kpc)[3]
Apparent magnitude (V)9.6[4]
Apparent dimensions (V)6.9′[4]
Physical characteristics
Absolute magnitude−8.21[2]
Mass5.36×105[5] M☉
Metallicity = −0.66[2] dex
Other designationsGCL 85
See also: Globular cluster, List of globular clusters

NGC 6539, or GCL 85, is a globular cluster of stars in the constellation Serpens. It was discovered by Danish astronomer Theodor Brorsen in 1856.[6][7] This cluster is visible with a small amateur telescope, having an apparent visual magnitude of 9.6 and an angular size of 6.9″.[4] It is located at a distance of 26.63 kly (8.165 kpc) from the Sun,[3] and 10 kly (3.1 kpc) from the Galactic Center.[2]

This cluster is located in the outer parts of the Galactic bulge. There is a large dark cloud complex located in the fore of this cluster, causing reddening from extinction.[8] NGC 6539 has a core radius of 0.54′, a half-mass radius of 1.67′, and a tidal radius of 21.5′. Compared to other globular clusters, NGC 6539 is considered metal rich, indicating that it has a relatively higher abundance of elements more massive than helium. Thirteen variable stars have been detected within 7′ of the core, of which a dozen are long period variables.[9] A millisecond pulsar was discovered in 1990.[10]

  1. ^ Cite error: The named reference hcob849_11 was invoked but never defined (see the help page).
  2. ^ a b c d e Cite error: The named reference Di_Criscienzo_et_al_2006 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference Baumgardt_Vasiliev_2021 was invoked but never defined (see the help page).
  4. ^ a b c Cite error: The named reference Gilmour_2012 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference apj742_1_51 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference Normandin_2000 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Patterson_2007 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Origlia_et_al_2005 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Baker_et_al_2007 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference D'Amico_et_al_1990 was invoked but never defined (see the help page).