NGC 1261

NGC 1261
NGC 1261 from Hubble Legacy Archive
Observation data (J2000.0 epoch)
ClassII[1]
ConstellationHorologium
Right ascension03h 12m 16.21s[2]
Declination–55° 12′ 58.4″[2]
Distance53.5 kly (16.4 kpc)[3]
Apparent magnitude (V)8.63[4]
Apparent dimensions (V)12.9′
Physical characteristics
Absolute magnitude−7.81[5]
Mass3.41×105[6] M☉
Metallicity = −1.38±0.14[5] dex
Estimated age10.24 Gyr[7]
Other designationsGCL 5,[4] ESO 155-SC11, Caldwell 87, Melotte 19
See also: Globular cluster, List of globular clusters

NGC 1261 (also known as Caldwell 87) is a globular cluster of stars in the southern constellation of Horologium, first discovered by Scottish astronomer James Dunlop in 1826. The cluster is located at a distance of 53 kilolight-years from the Sun, and 59 kilolight-years from the Galactic Center.[3] It is about 10.24[7] billion years old with 341,000[6] times the mass of the Sun. The cluster does not display the normal indications of core collapse, but evidence suggests it may have instead passed through a post core-collapse bounce state within the past two billion years. The central luminosity density is 2.22 L☉·pc−3, which is low for a globular cluster.[8] Despite this, it has a Shapley–Sawyer Concentration Class of II,[1] indicating a dense central concentration.

A total of 22 RR Lyrae variables have been discovered in this cluster, along with two long-period variables, three SX Phoenicis variables, and an eclipsing binary.[9] It was determined to be an Oosterhoff type I cluster, based on the periods of fourteen of the RR Lyrae variables.[10] 18 probable blue straggler candidates have been identified.[5]

  1. ^ a b Cite error: The named reference hcob849_11 was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference aj140_6_1830 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference aj139_2_476 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  5. ^ a b c Cite error: The named reference Kravtsov2010 was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference apj742_1_51 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference mnras404_3_1203 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Simunovic2014 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Salinas2016 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Wehlau1977 was invoked but never defined (see the help page).