Henry Draper Catalogue - History

History

The origin of the Henry Draper Catalogue goes back to the earliest photographic studies of stellar spectra. Henry Draper made the first photograph of a star's spectrum showing distinct spectral lines when he photographed Vega in 1872. He took over a hundred more photographs of stellar spectra before his death in 1882. In 1885, Edward Pickering began to supervise photographic spectroscopy at Harvard College Observatory, using the objective prism method. In 1886, Draper's widow, Mary Anne Palmer Draper, became interested in Pickering's research and agreed to fund it under the name Henry Draper Memorial. Pickering and his coworkers then began to take an objective-prism survey of the sky and to classify the resulting spectra.

A first result of this work was the Draper Catalogue of Stellar Spectra, published in 1890. This catalogue contained spectroscopic classifications for 10,351 stars, mostly north of declination −25°. Most of the classification was done by Williamina Fleming. The classification scheme used was to subdivide the previously used Secchi classes (I to IV) into more specific classes, given letters from A to N. Also, the letter O was used for stars whose spectra consisted mainly of bright lines, the letter P for planetary nebulae, and the letter Q for spectra not fitting into any of the classes A through P. No star of type N appeared in the catalogue, and the only star of type O was the Wolf-Rayet star HR 2583.

Antonia Maury and Pickering published a more detailed study of the spectra of bright stars in the northern hemisphere in 1897. Maury used classifications numbered from I to XXII; groups I to XX corresponded to subdivisions of the Draper Catalogue types B, A, F, G, K, and M, while XXI and XXII corresponded to the Draper Catalogue types N and O. She was the first to place B stars in their current position, prior to A stars, in the spectral classification.

In 1890, the Harvard College Observatory constructed an observation station in Arequipa, Peru in order to study the sky in the Southern Hemisphere, and a study of bright stars in the southern hemisphere was published by Annie Jump Cannon and Pickering in 1901. Cannon used the lettered types of the Draper Catalogue of Stellar Spectra, but dropped all letters except O, B, A, F, G, K, and M, used in that order, as well as P for planetary nebulae and Q for some peculiar spectra. She also used types such as B5A for stars halfway between types B and A, F2G for stars one-fifth of the way from F to G, and so forth.

Between 1910 and 1915, new discoveries increased interest in stellar classification, and work on the Henry Draper Catalogue itself started in 1911. From 1912 to 1915, Cannon and her coworkers classified spectra at the rate of approximately 5,000 per month. The catalogue was published in 9 volumes of the Annals of Harvard College Observatory between 1918 and 1924. It contains rough positions, magnitudes, spectral classifications, and, where possible, cross-references to the Durchmusterung catalogs for 225,300 stars. The classification scheme used was similar to that used in Cannon's 1901 work, except that types such as B, A, B5A, F2G, and so on, had been changed to B0, A0, B5, F2, and so on. As well as the classes O through M, P was used for nebulae and R and N for carbon stars.

Pickering died on February 3, 1919, leaving 6 volumes to be overseen by Cannon. Cannon found spectral classifications for 46,850 fainter stars in selected regions of the sky in the Henry Draper Extension, published in six parts between 1925 and 1936. She continued classifying stars until her death in 1941. Most of these classifications were published in 1949 in the Henry Draper Extension Charts (the first portion of these charts was published in 1937.) These charts also contained some classifications by Margaret Walton Mayall, who supervised the work after Cannon's death.

The catalogue and its extensions were the first large-scale attempt to catalogue spectral types of stars, and its construction led to the Harvard classification scheme of stellar spectra which is still used today.