Ah, it makes sense now. I didn't read your post closely enough. My apologies.

I love knowing there's more behind a pretty picture than just what you see!

NGC 4755 – THE JEWEL BOX “The Jewel of the South”

http://homepage.mac.com/andjames/Page001.htm

As a comment, it is a pity you didn't mention that the main cluster stars are not the only components of the cluster. The star in the upper left-hand corner is also a member, which shares similar proper motions and small parallax as the colourful A-shaped asterism. It listed as HIP 62646 (Hipparcos) and is the brightest component at 5.7v magnitude.

Secondly, Abbott did suspect there were colour changes in the cluster (as he did with the Eta Carina Nebulae). However, H.C. Russell did not measure the 129 stars in the open cluster to search for colour changes, but did so because he suspected the stars had moved because of the discrepancies in between James Dunlop and John Herschel's drawing of the stars. Colour to Russell was of minor consequent, who saw the majority of stars as "greenish". Of course, these motions were undetectable, manly as the proper motions are smaller than this and could only be noted in centuries or even millennia – roughly <5 kms^-1.
As to the Coal Sack (Richard Allen's "The Black Magellanic Cloud") and the cluster there is no really association. The distance of the Coalsack is 300 light years, NGC 4755 is much further away.
As to the evoution, the other interpretation is that the second branch of the main sequence (Page007.htm in the reference article below.) means that there might be just two stages of
formation (as stated in Sager and Cannon (1995) article [. Sagar, R., Cannon, R.D., ; A deep CCD photometric study of the moderately young southern open clusterNGC 4755 = κ Crucis” Astro.&Astroph. “Sup.Ser., 111, 75-84 (1995)] ). Here the main massive stars are formed, followed by another star formation period for the smaller components, whose ages differ by about 3 to 6 million years. The best estimation of date is probably Ivan Koenig (1998) 12.6±0.1 M.yr. [Koenig, I.; et.al. “Celebrating the 12589254th birthday of Herschel’s Jewel Box” Astronomische Gesellschaft Meeting (AGM), 14, p.35 Jan (1998)]

The other cluster NGC 4815 (12h 58.0m -64 deg 58') within the Coalsack (in Musca), which suffers greatly from interstellar absorption, shows significant evidence of a double main sequence. Its B-V lines are separated by about one B-V magnitude, and is one of the significant of this phenomena.. An excellent article about these dual main sequence clusters, is; “Stellar photometric stability. II. Ages and
distances for 13 open clusters with time series observations.” by Kjeldsen and Frandsen (A&A.,Sup.Ser., 87, 119 (1991)) Another is good NGC 4815 paper is In 1998, the latest paper (Chen, B. et.al. “The spatial distribution and luminosity function of the open
cluster NGC 4815.”; A&A., 331, 916-924 (1998)) , which discussed this problem you allude to for the Jewel Box – so-called "mass segregation" and the sudden drop-off of stars near the edges of open clusters. Clearly this is related to the open cluster formation process, and in how the embryonic nebulous condenses to produce stars. The important point is that stars are unlikely to form at precisely one instant or moment, but is a gradual process over million of years. "Isocrones" (start date for the star formation stage) for cluster formation are not necessarily single but maybe two (or even more) bursts of activity.

Those further interested in the Jewel Box (for background), especially its history, might like to refers to the Southern Astronomical Webpage at

Anyway, thanks for the article, especially the updates on investigation of the cluster and its stars..

As a comment, it is a pity you didn't mention that the main cluster stars are not the only components of the cluster. The star in the upper left-hand corner is also a member, which shares similar proper motions and small parallax as the colourful A-shaped asterism. It listed as HIP 62646 (Hipparcos) and is the brightest component at 5.7v magnitude.

Secondly, Abbott did suspect there were colour changes in the cluster (as he did with the Eta Carina Nebulae). However, H.C. Russell did not measure the 129 stars in the open cluster to search for colour changes, but did so because he suspected the stars had moved because of the discrepancies in between James Dunlop and John Herschel's drawing of the stars. Colour to Russell was of minor consequent, who saw the majority of stars as "greenish". Of course, these motions were undetectable, manly as the proper motions are smaller than this and could only be noted in centuries or even millennia – roughly <5 kms^-1.
As to the Coal Sack (Richard Allen's "The Black Magellanic Cloud") and the cluster there is no really association. The distance of the Coalsack is 300 light years, NGC 4755 is much further away.
As to the evoution, the other interpretation is that the second branch of the main sequence (Page007.htm in the reference article below.) means that there might be just two stages of
formation (as stated in Sager and Cannon (1995) article [. Sagar, R., Cannon, R.D., ; A deep CCD photometric study of the moderately young southern open clusterNGC 4755 = κ Crucis” Astro.&Astroph. “Sup.Ser., 111, 75-84 (1995)] ). Here the main massive stars are formed, followed by another star formation period for the smaller components, whose ages differ by about 3 to 6 million years. The best estimation of date is probably Ivan Koenig (1998) 12.6±0.1 M.yr. [Koenig, I.; et.al. “Celebrating the 12589254th birthday of Herschel’s Jewel Box” Astronomische Gesellschaft Meeting (AGM), 14, p.35 Jan (1998)]

The other cluster NGC 4815 (12h 58.0m -64 deg 58') within the Coalsack (in Musca), which suffers greatly from interstellar absorption, shows significant evidence of a double main sequence. Its B-V lines are separated by about one B-V magnitude, and is one of the significant of this phenomena.. An excellent article about these dual main sequence clusters, is; “Stellar photometric stability. II. Ages and
distances for 13 open clusters with time series observations.” by Kjeldsen and Frandsen (A&A.,Sup.Ser., 87, 119 (1991)) Another is good NGC 4815 paper is In 1998, the latest paper (Chen, B. et.al. “The spatial distribution and luminosity function of the open
cluster NGC 4815.”; A&A., 331, 916-924 (1998)) , which discussed this problem you allude to for the Jewel Box – so-called "mass segregation" and the sudden drop-off of stars near the edges of open clusters. Clearly this is related to the open cluster formation process, and in how the embryonic nebulous condenses to produce stars. The important point is that stars are unlikely to form at precisely one instant or moment, but is a gradual process over million of years. "Isocrones" (start date for the star formation stage) for cluster formation are not necessarily single but maybe two (or even more) bursts of activity.

Those further interested in the Jewel Box (for background), especially its history, might like to refers to the Southern Astronomical Webpage at
http://
homepage.mac.com/andjames/Page001.htm

Anyway, thanks for the article, especially the updates on investigation of the cluster and its stars..

Brightly cold and very old
Rubies beyond price,
Diamonds beyond measure,
And sapphires all comprise
The bounty of this treasure.

The answer of course is 'stars'. A box of precious jewels indeed.

Winchell? Some stellar extinction could possibly have occured in the Jewel Box according to Fresneau, Vaughan, and Argyle; "The weak distant encounter of stars with the cold neutral medium can be explained by a mean mass of about 2500+/-1250 Msolar for the gas and dust content in order to account for the diffusion of stellar orbits. A mean displacement of 0.012"+/-0.001" yr-1 of the western limb of the Southern Coalsack is estimated in the northwest direction and permits a search for strong close stellar encounters. The transfer of angular momentum between the interstellar medium and the scattering of stellar orbits resulting from the encounters suggests a dissipation rate of (2.0+/-0.7)×10-4 Msolar yr-1, leading to an equipartition time of 12+/-4 Myr. A spin rate of 0.25+/-0.05 km s-1 pc-1 of the diffuse clouds in the Southern Coalsack is measured and interpreted as the result of the perturbation induced by stellar systems during flyby encounters with a crossing time of 3 Myr, suggesting a cloud core radius of 1 pc."

I should have been more precise that its not neccessarily interacting with NGC 4755 as much as it is blocking our view.

Gerald

too much!

Error corrected and thanks for the heads up!

That's a factor 1000 to much, I suppose