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Cosmic Challenge: IC 4997
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Cosmic Challenge:
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This month's suggested aperture range: |
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6- to 9.25-inch (15-24cm) telescopes |
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Target |
Type |
Constellation |
RA |
Dec |
Magnitude |
Size |
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IC 4997 |
Planetary nebula |
Sagitta |
20h 20.1m |
+16° 43.9’ |
11.2 |
2.7"x1.4" |
This month’s challenge, the planetary nebula IC 4997 lies within the borders of Sagitta, and is surprisingly bright, but extremely small. That combination makes this a great object for everyone, whether you are observing under the veil of light pollution or from a dark, rural location. Its intensity should shine through all but the most extreme situations.
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Above: Evening star map showing the location of this month's Cosmic Challenge. Credit: Map adapted from Star Watch by Phil Harrington
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Above: Finder chart for this month's Cosmic Challenge. Credit:
Chart adapted from Cosmic
Challenge: The Ultimate Observing List for Amateurs by Phil Harrington. |
Finding IC 4997 is confounded by its location. It lies in an empty void near the intersection of Sagitta and Delphinus, about halfway between 5th-magnitude Eta (η) Sagittae and 4th-magnitude Beta (β) Delphini. The bright stars in its immediate vicinity shine at only 7th magnitude. Three orangish suns -- SAO 105922, SAO 105947, and SAO 106035 -- form a right triangle just to its north and make a handy reference. IC 4997 is just south of the halfway point along the triangle's hypotenuse, marked by SAO 105922 and SAO 106035. There, you will see that IC 4997 forms a small obtuse triangle with a 10th-magnitude star situated just 1.1' to its southwest and a 12th-magnitude sun 2' to its west.
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Above: Rendering of NGC 7354 through the author's 8-inch (20.3 cm) f/7 Newtonian reflector at 127x. |
While it is easy to confuse those field stars for the planetary, they actually make handy comparison points when blinking the field with an O-III nebula filter. That's really the only way to confirm which is which, since IC 4997 remains perfectly stellar even at 300x. With a filter in place, however, the nebula will appear brighter than the 10th-magnitude star; with it removed, the star will outshine the planetary. The planetary's very subtle bluish tint may also help to identify it from among the field of white stars. When we look its way, we are viewing across approximately 8,000 light-years.
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Above: Image of IC 4997 taken by the author. South is up to match the sketch above. Details: Celestron Origin Home Observatory @ f/2.2, 30 minutes total exposure (1,800 subframes @ 10 seconds each). Insert: IC 4997 through the Hubble Space Telescope. Credit: Howard Bond (ST ScI) and NASA/ESA
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Scientific
observations of IC 4997 have revealed a rich spectrum of emission lines,
including those from ionized oxygen, nitrogen, and hydrogen, indicative of high
temperatures and densities within the nebula. Studies also show that this
little planetary varies in brightness. Long-term studies conducted by E. B.
Kostyakova of Moscow
Good luck with this month's challenge! Be sure to post your results in this column's discussion forum. And remember that half of the fun is the thrill of the chase. Game on!
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About
the Author: |
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Phil Harrington's Cosmic Challenge is copyright 2024 by Philip S. Harrington. All rights reserved. No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder. |
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- random, John O'Hara and UnityLover like this
13 Comments
Now that's my kind of challenge!
Clear skies!
Thomas, Denmark
Appreciate you Phil for letting us know about this very interesting target. A baby PN! It will be clear tonight and I will plan to chase it.
Thank you so much for these recommendations. I like viewing exotic objects.
Best wishes,
Larry, Indiana
V magnitude 11.15!!
But size 2.7" x 1.4" Almost stellar.
That's smaller than Neptune!
OMG, it's not in my list of observed objects in Sagitta.
OK, it's on my list. Looks like it needs a minimum of 400-500x, so I hope for good seeing.
Looks fun, just like IC 418 was! Cool to know! I might try it soon!
I didn't have seeing of sufficient quality to use the necessary magnification last night.
Sagitta will still be visible next month.
Got it with my Nexstar 11 at 87X and blinking an OIII. Then identified field stars using Phil's map to make a positive ID. So this was not hard as I have a larger scope then recommended and I had a 20.9 SQM reading in a not too transparent sky from smoke. Best for me is a SQM of 21.2 with good transparency.
The website philharrington.net seems to be down. Just a heads up!
Like Phil stated, it was stellar at all magnifications used, but I did not attempt to view it at over 300x.
Thanks, Phil for another fun challenge.
It's working now.
Observed on October 31st, 2013:
6" F/5 achro, OIII 10nm Baader filter, eyepiece f=16mm (magnification 47x), first blinked, then easily seen.
This planetary took me some time to navigate towards its expected position. Now I have a better finderscope.
Thanks for suggesting this planetary,
JG
The Stellafane 2022 - Nights of Future Passed youtube from your website was very enjoyable, thanks!
I got this image last night with a C8/Hyperstar. Love PN's!
A friend of mine and I observed IC 4997 last night using his rather unusual 20" classical Cassegrain at 203x. It was not that difficult a target with that aperture. We could see it well enough without filtration.
However, NGC 6879, also in Sagitta, was much harder to see.
https://www.go-astro.... NGC 6879 is a
We also looked at NGC 6891, which exhibited a faint bluish hue, and NGC 6905 (the Blue Flash Nebula) and NGC 6886, which were previous Cosmic Challenge objects.
NGC 1514 was the last planetary nebula that we viewed, this time at 159x. As usual, a nebula filter really enhanced the Crystal Ball Nebula.
During the course of the night, we also observed NGC 6934, NGC 7006, M36, M38, NGC 1907, M37, M42, and Jupiter.
Here's several observations I've made with different apertures --
8" (9/23/22): IC 4997, a very compact mag 10.8 planetary, has an ideal 10th mag comparison star (HD 355464) just 1' SW! Sliding a NPB filter into the light path, the PN dominated the nearby star by over a magnitude. Upping the power to 225x, IC 4997 wouldn't focus down to a sharp point and was definitely fuzzy at 325x.
14.5" (8/20/22): easy to identify at 66x just 1' NE of a brighter mag 10 star, though in a rich star field. Blinking with the OIII filter than PN seemed roughly 1 mag brighter than the comparison star. At 140x, it displayed a bluish color and was slightly non-stellar (more evident with averted vision), which was confirmed at 226x (perhaps 3" diameter). Excellent view at 660x with an evenly lit, high surface brightness disc.
14.5" (7/11/21): immediately recognized as a compact PN at 140x due to its typical soft blue appearance just 1' NE of a brighter mag 10 star. Adding a UHC filter the PN was noticeably brighter than the star and a tiny disc was clearly outlined. At 182x with a filter, I'd estimate the PN seemed 1 mag brighter than the star. A third 12th mag star just W complete an obtuse isosceles triangle. Increasing to 352x, the blue 3"-5" disc had a very high surface brightness. Also examined at 528x but didn't see any additional details. Located in a rich Sagitta star field 36' NW of the triple star STF 2670 (in Delphinus).
17.5" (8/18/01): the PN appears as an unusually bright mag 11 "star" (V = 10.8) at 100x in a rich star field. Verified with OIII blinking. An excellent comparison star is a mag 10 star just 1' SW. A 12th mag star 2' WSW completes a distinctive obtuse triangle. With the filter the PN is nearly one magnitude brighter than the 10th mag star. At 280x, the PN is bluish and a tiny disc was highly suspected, perhaps 2"-3".