2 Attachment(s)
Object Of The Week, January 17, 2016 - IC 1747
IC 1747, HD 11758, PK 130+01.1, PN G130.2+01.3
RA
01 57 35.734
DEC
+63 19 18.33
Type Planetary Nebula
Size 24.4" x 20.5"
Visual magnitude 12
Visual magnitude central star 15.8
Compared to the previous two OOTWs I am turning back the sidereal time a few hours :) We will take a look at the planetary nebula IC 1747 in Cassiopeia. At the moment of this writing it culminates south around the end of astronomical twilight.
IC 1747 was first mentioned in Harvard Circular #98 in 1905, which I cannot seem to find online, and then again in a paper called Nebulae Discovered at the Harvard College Observatory, Annals, vol. LX, no VI (page 150) as H. N. 103 (Harvard Nebula) in 1908 (http://adsabs.harvard.edu/abs/1908C%26T....29..302.). The first IC catalog was already published by then, so it was included in the second one. The Annals Of Harvard College Observatory credit Wilhelmina Pickering as the discoverer. Wilhelmina Fleming already was mentioned in several OOTWs (Campbell's Hydrogen Star, Swings Struve 1, The Horsehead's Visibility) so who was she and how did she discover so many objects?
Wilhelmina Pickering (1857 - 1911) came from Dundee, Scotland, to Boston, Massachusetts, only to find herself pregnant and abandoned by her husband. By chance she took on a job as housekeeper for Edward Charles Pickering, the director of Harvard College Observatory. Apparently,
There are two accounts of how this came about: “(1) in 1879 Pickering offered her a part-time position as a copyist and computer at the Observatory because he was ‘struck by her obviously superior education and intelligence,’ or, (2) a male assistant proved to be unsatisfactory and ‘in a huff Pickering is reported to have said...that he believed his housekeeper could do a better job.’” He was right on the last count. She did do a better job than his previous assistant.
(source http://www.womanastronomer.com/wfleming.htm)
Fleming got involved with cataloguing, indexing, examining, and care of the photographic plates with stellar spectra taken at the Harvard College Observatory for Henry Draper's catalog project. Only 12 years later, in 1898, Wilhelmina became the first woman to get an official astronomical job, in her case as Curator of Astronomical Photographs.
During her tenure at Harvard, Fleming discovered many celestial objects, including 79 stars, 10 novae, 59 gaseous nebulae, 94 Wolf-Rayet stars, and 222 variable stars, publishing an important list of the latter in 1907. She also helped to implement a system of assigning stars a letter according to how much hydrogen could be observed in their spectrum – stars classified as A had the most hydrogen, B the next most, and so on. This later became the famous series OBAFGKM.
Pickering employed many other women besides Fleming, who was the first. The group was referred to with the patronizing "Pickering's Harem". However, the success of the group women spread over other observatories and by the 1920s almost every large observatory in the USA hired women for similar jobs.
So, what about IC 1747 itself? At first it was thought to be an emission line star but as soon as 1918 it was already classified as a planetary nebula. IC 1747 at first mostly showed up in research about gas abundances in planetary nebulae but by the 70s also in radio research and distance measurements. Still, surprising little is to be found about this planetary nebula. It lies about 2.94 kpc from the Sun, 10.6 kpc from the galactic center and 67 pc from the galactic plane but that's about all I can find about this nebula (without actually reading through all the papers, that is).
I observed the nebula with my 20" on November 6, 2015. My notes read
At 83x already visible without filter. At 692x visible as a small, not quite complete disk. At one side, pointing towards a line between two stars, there seems to be a hole in the edge. There are two bright patches at the edges and a hole in the center. So it was seen as a C-shaped nebula with two bright spots.
I didn't notice the central star, which actually is quite faint compared to the nebula. The Belgian amateur Tom Corstjens observed the nebula with his C11 at 600x a few days earlier and created this incredible drawing
Attachment 1963
The drawing shows many of the features that I saw in my 20", though the hole in the ring was smaller when I looked at it than drawn by Tom and I don't recall having seen the central "bar". I found observing reports with instruments as small as 8" but the high brightness suggests it is visible in 6" telescopes, or even smaller, as well. I didn't try with my 6", however. Yet!
Of particular interest to the photographers among us may be the discovery in 2002 of a possible halo around the nebula. The paper, published in 2003 in the Monthly Notices of the Royal Astronomy Society http://mnras.oxfordjournals.org/content/340/2/417.full, contains this picture in which IC 1747 is shown in the center two images:
Attachment 1964
The halo looks exceedingly faint to me so I doubt it will be detectable visually in large telescopes, but you never know!
As always,
"Give it a go and let us know!
Good luck and great viewing!"
