NGC 1261
Globular cluster in the constellation Horologium
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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.
| NGC 1261 | |
|---|---|
NGC 1261 from Hubble Legacy Archive | |
| Observation data (J2000.0 epoch) | |
| Class | II[1] |
| Constellation | Horologium |
| Right ascension | 03h 12m 16.21s[2] |
| Declination | –55° 12′ 58.4″[2] |
| Distance | 53.5 kly (16.4 kpc)[3] |
| Apparent magnitude (V) | 8.63[4] |
| Apparent dimensions (V) | 6.9′ |
| Physical characteristics | |
| Absolute magnitude | −7.81[5] |
| Mass | 3.41×105[6] M☉ |
| Metallicity | [Fe/H] = −1.38±0.14[5] dex |
| Estimated age | 10.24 Gyr[7] |
| Other designations | GCL 5,[4] ESO 155-SC11, Caldwell 87, Melotte 19 |
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]
