HISTORY of the JEWEL BOX

PART THREE : E. 1900 — 1920

As we have discussed in some detail one of the earliest observations of the Jewel Box in Australia was by Victorian observer Francis Abbott in 1862, who pointed out possible changes in both the stellar positions and some of the star colours. Innes also noted this again in 1906. Strong debate on the subject started in 1908, likely initiated by James Nangle, who by 1927 was to eventually become the Government Astronomer at Sydney Observatory. Discussions feature in the J.BAA., 18, 384 (1908), with the debate continued in J.BAA, 19 followed by R.A. Proctor in 1915 in J.BAA., 27, 29 and 30. Each debated such positional changes on the grounds of detecting “alleged” true stellar motions within the cluster — a sure indication of distance. Photography sufficiently improved evidence for proper motions in the mid-1920s, and the production of the first suitable plates in various colours featuring NGC 4755 stars. Between 1900 and 1920, other than several observational descriptions of this object, like that of Sydney amateur Walter Gale, data from this era now can only be considered as general information.

Probably, one of the best quotes from this period was made by R.T.A. Innes (1908) in the updated classic “Celestial Objects for Common Telescopes” by Rev. Thomas Webb says of the Jewel Box:

“Vivid and beautiful cluster, fifty to one hundred [stars] of various colours, some greenish, round Kappa Crucis, extremely red.”

F. 1920 — 1950

In 1925, the earliest spectral analysis of the component stars was achieved by Robert Julius Trumpler (1886-1956) in his classic paper ‘Spectral Types in Open Clusters’. It is likely that this work inspired another close inspection of the Jewel Box, and this continued with numerous publications, at least until the culmination of the classic book, Harlow Shapley’s “Star Clusters”. Harvard Observatory’s Monograph No. 2 (1930). It was Shapley and Melotte who classed the Jewel Box as Type ‘g’ — considerably rich and concentrated. In 1929, Trumpler used only thirty stars within the inner 6′ radius and gave NGC 4755 the more modern ‘I 3 r − ’ classification, which first appeared in “Preliminary Results on the Distance, Dimensions, and Space Distribution of Open Star Clusters.”, Lick Obs.Bull., 14, 154 (1930). ‘The I 3 r -’ stating:

“Detached, strong concentration, bright and faint stars in the cluster, rich in stars, without nebulosity.”

As the original data on the southern cluster was so scant, it was eventually Ruprecht who confirmed this initial classification (Bull. Astron. Inst. Czech., 17, 34 (1966)).

Last Update : 23rd September 2012

Southern Astronomical Delights © (2012)

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