Sky & Telescope - August 2023 - 22

Prolific Astronomer
their photographic magnitudes. The alphabet soup of spectroscopic
types ran from A through N, based on the strength
of the hydrogen absorption lines, called the Balmer series. In
addition, she assigned the letter O to Wolf-Rayet and other
emission-line stars, P to planetary nebulae, and Q to oddballs.
Annie Jump Cannon later simplified and refined this
system to the familiar O, B, A, F, G, K, and M types that we
still use today.
Fleming identified 30 planetary nebulae when analyzing
the objective-prism plates of the Henry Draper Memorial.
She included these in lists of objects with peculiar spectra
(variables, carbon stars, Wolf-Rayets, and nebulae) published
in Harvard College Observatory Circulars and the
Astrophysical Journal.
While examining a plate taken in 1888 of the Orion
Nebula (M42), Fleming discovered the galaxy IC 421 and 10
reflection nebulae. Her analysis also revealed a new emission
nebula (IC 434) with a " semicircular indentation 5′ in
diameter " - the iconic dark nebula known as the Horsehead
Nebula! John Louis Emil Dreyer credited Pickering - as the
observatory's director - with discovering these dozen objects
in his 1895 edition of the Index Catalogue (IC). In 1908, Pickering
published a complete table of nebulae found by HCO
astronomers between 1848 and 1907, noting who discovered
them. He set the record straight on IC 434 but didn't mention
Fleming's famous dark indentation.
LET'S CALL IT BY ITS NAME Concerted efforts are being made to
honor Williamina Fleming as the discoverer of these ethereal wisps in the
Veil Nebula in Cygnus, which are still commonly referred to as Pickering's
Triangle. Hopefully you'll start to see it more often labeled Fleming's
Triangular Wisp.
leaving to get married. Fleming also assumed responsibility for
examining, classifying, and storing the expanding collection
of glass plates. In 1899, Harvard Corporation (one of Harvard
University's two governing bodies) appointed her as Curator
of Astronomical Photographs, making her the first woman to
hold either an observatory or a Harvard University title.
She trained and led a cadre of female " computers, " including
the remarkable trio of Henrietta Leavitt, Antonia Maury,
and Annie Jump Cannon. The work was tedious, and the
women were vastly underpaid. But the spectral classification
of stars was pivotal in unlocking their chemical composition,
physical properties, and evolution.
Fleming's major spectroscopic work appeared in the Draper
Catalogue of Stellar Spectra, published in 1890 as Volume 27
of the Harvard Annals. Using a scheme later dubbed the
Pickering-Fleming System, she cataloged the spectra of more
than 10,000 stars north of declination -25° and measured
22 AUGUST 2023 * SKY & TELESCOPE
Mina's Marvelous Finds
R Aquarii is a fascinating Mira-type variable (a cool, pulsating
supergiant) with a period of 387 days and a visual magnitude
ranging from 5.2 to 12.4. German astronomer Karl
Ludwig Harding discovered the star's variability in 1811, and,
during the century that followed, astronomers considered it a
typical long-period variable. Fleming first detected a nebular
emission line in 1893. Her log entry from October 17th reads,
" faint nebular band 5007, and bright hydrogen lines Hβ
[hydrogen-beta] to Hδ [hydrogen-delta] visible, with no trace
of the M spectrum. "
In 1919, Mount Wilson Observatory astronomer Paul
Merrill obtained a spectrum with the 100-inch Hooker telescope
and found conspicuous O III emission lines at 5007,
4959, and 4363 angstroms. He noted, " The spectrum may
be described as a combination of that of a gaseous nebula
with that of a typical star of Class Md [modern classification
M7e]. " In 1922, a third spectrum of the target exhibited
bright lines of hydrogen, helium, and iron, indicating
a hot companion of class O or B. Merrill closely monitored
remarkable changes in the spectral features from 1928
through 1949.
Lowell Observatory's Carl Lampland photographed the
variable in 1921 with the 40-inch reflector and discovered the
very peculiar R Aquarii Nebula (also Cederblad 211) associated
with the star. Lampland reported, " the most conspicuous
detail of this structure is an oval-shaped configuration
composed of arcs of well-defined nebular filaments. "
SARA WAGER
Sky & Telescope - August 2023

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