sponsored by psychohistorian.org
RA: 20h 20m 8.74s
Dec: +16° 43′ 53.7″
Ch: MSA:1217, U2:208, SA:16
Type: planetary nebula
Mag: B=12, V=11
The young planetary nebula IC 4997, mentioned in recent postings by Doug Snyder and Steve Coe is remarkable by changes of emission lines intensity. The best documented is the close pair of lines at 436.3 nm (another forbidden line of doubly ionized oxygen) and H_gamma (434.0 nm). Their intensity ratio changed considerably in the past between 1.6 - 0.6. Variations of these and other lines in visual spectrum lead to variations of the total magnitude of the planetary (long-term, a few tenths of magnitude), which was therefore designated QV Sge. There are several other planetaries with a variable-star name associated, but those refer to their central stars (including even some eclipsing binaries). Activity in IC 4997 is dramatically illustrated in a recent paper by Miranda and Torrelles (ApJ 496:274, 1998), who found that radio morphology of the planetary changes since 1995! Clear skies, Leos
[amastro] Re: IC 4997 = QV Sge
Although the variations in the nebular emission lines of IC 4997 are certainly real, I am quite skeptical of the reported broadband photometric variations. The seris of papers by Arkhipova et al. about this object are simply unconvincing in terms of internal errors, long-term stability, etc. As I've written in the late-lamented "CCD Astronomy", this would make a good project for someone with a small telescope + CCD. Brian
I don't have the papers at hand, but as regards photometry, I trust Brian ;-) Unfortunately, it's rare to find a technical paper where one can rely on the authors' conclusions and don't have to go to their data and lines of reasoning. Best, Leo
Steve Coe, observing with a 13" f/5.6, notes: "Pretty bright, very, very small, somewhat brighter in the middle at 165X. Not much larger than the Airy disk."
(PK58-10.1) Mag=11.3. Sagitta: 20h, 20.2m; +16°, 45' This tiny (2") slightly oval planetary is almost stellar at low powers; it is revealed as a near-disk at 200x to 400x in my 8" aperture scope. It was not too difficult to verify once the proper eyepiece field was found. In a heavily light-polluted environment, we're sure an oxygen- nebula filter will make a great difference in being able to discern this object as distinct from the field stars: in a sky with a naked-eye stellar magnitude limit of about 5.5, the filter was not absolutely necessary to confirm the object, though it did assist.
16-inch f/10 SCT (127x, 290x)
Extremely small and stellar. However with averted vision it display a hazy star like image. A O-III filter brings out the very soft envelope which let it grows slightly in size.
Observing site: Little Bennett Regional Park
[20h 20m 12s, 16° 45m 0s] A blue star that vanished when looked at directly. Looks brighter than 12mv.
The Messier objects
The Bennett objects
The Caldwell list
DOCdb is still in beta-release.
Known issues, feature requests, and updates on bug fixes, are here:
Found a bug? Have a comment or suggestion to improve DOCdb? Please let us know!
DOCdb is a free online resource that exists to promote deep sky observing.
You could help by sharing your observations, writing an article, digitizing and proof-reading historical material, and more.
Everything on DOCdb.net is © 2004-2010 by Auke Slotegraaf, unless stated otherwise or if you can prove you have divine permission to use it. Before using material published here, please consult the Creative Commons Attribution-Non-Commercial-Share Alike 2.5 License. Some material on DOCdb is copyright the individual authors. If in doubt, don't reproduce. And that goes for having children, too. Please note that the recommended browser for DOCdb is Firefox 3.x. You may also get good results with K-Meleon. Good luck if you're using IE. A successful experience with other browsers, including Opera and Safari, may vary.