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NGC 5139

Shim1Pel.gif (799 bytes) Omega Centauri Shim1Pel.gif (799 bytes) Flamsteed designation (1712, 1725) Shim1Pel.gif (799 bytes)
De Chéseaux 18 De Chéseaux's list (1746)
Lacaille I.5 Lacaille's catalogue (1755)
Dunlop 440 Dunlop's catalogue (1828)
Shim1Pel.gif (799 bytes) NGC 5139 Shim1Pel.gif (799 bytes) New General Catalogue (Dreyer, 1888) Shim1Pel.gif (799 bytes)

Synopsis

Globular cluster; located in Centaurus; R.A. 13:26:46, dec. -47:28:37; culmination late May; magnitude 3.6; distance 5,000 pc (approx 16,300 light years).

Description

By far the largest and most spectacular of the galactic globular clusters. Recorded as a star by Ptolemy and (as w Centauri) by Bayer.

The main region is about 20' in diameter, though the exact boundary of any globular cluster is somewhat arbitrary, and broadly compressed towards the centre though the distribution is not uniform.
Property Value Notes/References
R.A. 13:26:45.89 ICRS 2000.0
Declination -47:28:36.7 ICRS 2000.0
Precession in RA    
Precession in dec.    
Proper Motion RA   Includes the cos(dec) term.
Proper Motion dec    
Radial Velocity +238 Km/s Simbad
Parallax    
Distance 5,000 pc Malin & Frew 1995
Integrated mv 5.33
3.6		 Simbad
Tirion 1991
Integrated Mv -10.07 Djorgovski 1993, p. 377
Integrated B-V 0.15 Pryor & Meylan 1993, p. 370
Concentration
'c' of Pryor & Meylan 1993		 1.2 (defined as tidal radius/scale radius, Pryor & Meylan 1993, p. 361) Pryor & Meylan 1993, p. 370
Cluster Mass 3.98 x 106 (log M = 6.6) M¤ Pryor & Meylan 1993, p. 370
Mass to Light Ratio (M/Lv) 3.6 Pryor & Meylan 1993, p. 370
Table 1: Known Parameters for NGC 5139.

Discussion

Study of red giant branch stars in Omega Centauri by a team of astronomers using the 0.9-meter telescope at Cerro-Tololo Interamerican Observatory in Chile (Lee et al. 1999) has revealed several distinct stellar populations within the cluster, with ages ranging over at least 2 Gyr.

The team observed more than 130,000 stars, obtaining a color-magnitude diagram (CMD) for 50,000 member stars which indicates that the stars of this cluster did not all form at once but over a 2-billion-year period of time, with several starburst peaks. This was the first time that multiple populations have been reported in a globular cluster.

The team who carried out this work speculates that this result may indicate that Omega Centauri might be the remnant of a nucleus of a dwarf galaxy which has merged with our Milky Way.

Observation

Some authors claim that the cluster can be seen with the naked eye (e.g. as "a hazy patch of light" – Moore 1972, p. 100) but I have never seen it this way. However, it is an easy target for 7 x 50 binoculars and a spectacular sight in any aperture telescope.

Further Resources

References

Djorgovski, S. 1993: Physical Parameters of Galactic Globular Clusters. In Djorgovski, S.G.; Meylan, G.: Structure and Dymanics of Globular Clusters. ASPC Series, Vol. 50.

Lee, Y.-W., Joo, J.-M., Sohn, Y.-J., Rey, S.-C., Lee, H.-c., & Walker, A. 1999: The Globular Cluster Omega Centauri: A Relic of a Galactic Building Block. Nature 402: 55.

Malin, David; Frew, David 1995: Hartung’s Astronomical Objects for Southern Telescopes. 2nd ed.

Moore, Patrick 1972: The Southern Stars. Whitcombe & Tombs.

Pryor, Carlton; Meylan, Georges 1993: Velocity Dispersions for Galactic Globular Clusters. In Djorgovski, S.G.; Meylan, G.: Structure and Dymanics of Globular Clusters. ASPC Series, Vol. 50.

Tirion, Wil 1991: Cambridge Star Atlas 2000.0. Cambridge University Press.

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