AGE of the JEWEL BOX

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Some debate still exists on the age of NGC 4755. Earlier references once quoted one hundred million years, though most of the more recent estimates have significantly reduced this value. The general trends of many quoted distances in the last fifty years follow:


   Schmidt ("Astronomische Nachrichten", 287, 41 (1963))
 

1 030 million years

   Barbaro (1967)
 

8 million years
   Abt. H.A; AJ, 241, 275 (1980)) and this particular value
   is still quoted in the "5th Lund Catalogue of Open Clusters"(1987)


34 million years

   Ward et. al. (1984)
 

22.4 million years

   Dachs, J., & Kaiser, D., Astron.&Astroph., 58, 411 (1984)
 

8 to 11 million years
   Frandsen, S., & Kjeldsen, H., "Stellar Photometric Stability. II.
   Ages and distances for 13 open dusters with time series observations",
   Astron.&Astroph. Sup. Ser., 87. 119-152 (1991)

5 and 8
million years

   Maeder and Meynet, Astron.&Astroph.., 87, 451 (1991)
 

8 to 12 million years
   Sagar, R., Cannon, R.D., Astro.&Astroph. Sup.Ser., 111, 75-84 (1995);
   “A deep CCD photometric study of the moderately young southern open cluster
   NGC 4755 = κ Crucis”

6 to 7 million years
   Koenig, I.; et.al.Celebrating the 12589254th birthday of Herschel's Jewel Box”;
   Astronomische Gesellschaft Meeting (AGM), 14, p.35 Jan (1998)


12.60.1 million years.

This last value of Cannon and Sagar seems to be the best of the modern estimations, though Sagar and Cannon suggest that the brighter components of the cluster may be perhaps some 4 million years older. Several of the later investigations also seem to be confirming this; Ie. Koenig, I.; et.al. (1998) and using more recent evolution theory suggest 12.60.1 Myr. (Calculating as the 12589254 years appearing in this papers title!)

Another of the most recent investigations by Sanner., J., Brunzendorf., Will J.M-, Geffert, M.,;"Photometric and kinematic studies of open star clusters II, NGC 4103, NGC 5281 and NGC 4755." Astron.Astrophys., 369, 511-526 (2001) concluded "...ages at most of t=45Myr.",  setting the maximum age. There is some evidence that clusters do not produce individual stars all at once and that the process may occur of several million years. Such ideas explain the evolutionary variations seen in the colour magnitude diagrams. It is even possible that one (or more) bursts of star formation occur giving the appearance that they are seemingly two star clusters. There is much to be said on this particular topic about open cluster - something which will warrant future investigation and observations. In some ways, the value of the age of any young cluster maybe less important than the range of the ages of its individual stars.

NGC 4755 overall is a very young cluster compared with most in the sky. Next we shall compare the Jewel Box to some other southern clusters.



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Last Update : 05 April 2002

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