Object of the Week July 24th, 2022 - IC4634

[obrazell]

IC 4634

ESO 587-1

Planetary nebula

Ophiuchus

R.A. 17h01m33.6s

Dec. -21°49'34" (2000)

Magnitude: 12.00

Sie 11” x 9”

Continuing last week’s theme of planetary nebulae I have chosen the small planetary nebula IC 4364 in Ophiuchus
for this week’s object. Discovered from its spectrum by Fleming in 1894 its small size and southern location meant
that there are no recorded amateur observations of it until about 1955 when Hartung observed it and included
it in his book Astronomical Observations for Southern telescopes. He suggested a minimum aperture of 15cm
was needed to show the disk but that smaller apertures may show it by its spectrum. It certainly did not
seem well known enough in the late 1970’s/early 80’s to make either the WSDSOH Vol2 or L&S. I note
that Steve Gottlieb did see it with a 20cm scope in 1982. Certainly, by the time the NSOG was compiled
more people were looking at it and as expected all observations reported suggested using high powers of
more than 200x.

ic4634.jpg

The distance as always with planetary nebulae is uncertain but IC 4634 is believed to lie
more than 7500 light years away. A fine Hubble image of it can be seen here
https://esahubble.org/images/potw1003a/. The main shape of the nebula is the remarkable double
S-shape, although there are other features that suggest that there may have been multiple ejection
events in the past. The fact these do not all lie on the same axis suggests that the source was
precessing and leads to the suggestion that the central star may be in a binary system. IC 4634 also
shows signs of shock excited features which have occurred as the jet has interacted with the local ISM.

potw1003a.jpg
Credit ESA/NASA

From its spectrum it appears that IC 4634 may have been formed by a metal poor star leaving
behind a CSPN of perhaps 0.55 solar masses with a temperature of about 55000K. The magnitude
the CSPN is about 14 but it is difficult to see because of the brightness of the nebula itself. The
central star is classified to be of the [WR] type. The nebula itself is classified as an archetypical
example of the point symmetric type.
The size of the nebula is likely to be the challenge when finding it rather than the brightness given
its size of the order of 11” x9” it is going to look stellar at low powers. It does appear to respond to
both OIII and UHC type filters and I would suggest on acquisition using the highest power the
conditions and telescope will allow. It will probably only show a disk but the largest amateur
telescopes may show some detail. I note that IC 4634 has also made the AL Planetary Nebula
club list as well.

As always give it a go and Lets us Know what you find

[lamperti]

With a 20" at 272x: "Can see it without filter but UHC brightened it up. Stellar disk is bright, dense and homogeneous."
With a 10" at 87x + UHC: "A very bright star-like object that brightens with filter. No shape discerned."

[wvreeven]

I was able to identify it as a planetary nebula using my 6" home built Newtonian telescope back in 2005 using an OIII filter. It remained stellar, even at a magnification of 170x.

[Bertrand Laville]

Hi All,

Here is my observation with a 25" Obsession
Report: http://www.deepsky-drawings.com/ic-4634/dsdlang/fr

Clear sky
Bertrand
http://www.deepsky-drawings.com/

IC 4634 T635 BL 2020 05 25.jpg

[Raul Leon]

Hi, here's my observation from 3/13/2010: Ic 4634 is a planetary nebula in Ophiuchus ; magnitude: 12 ; size: 11" x 9" ; small, roundish, fairly bright ; observed pale blue color, especially in low power, no central star observed. I used a 10mm Radian at 198x with my 14.5 Starstructure f/4.3ic 4634.jpg

[KidOrion]

07/25-07/26/20
THE OXBOW
SUNSET: 8:44 PM
MOON: 6 days (set at 11:57 PM; 32% illuminated)
SEEING: 6
TRANSPARENCY: 8
SQM: 21.53-21.63
NELM: not checked
WEATHER CONDITIONS: temps to upper 60s; light dew; breezy
OTHERS PRESENT: LR (18”), AG
All observations: 12.5" f/5 Discovery Dob, 14mm ES 82? eyepiece (112x, 0.7? TFOV) unless otherwise noted

11:54
IC 4634 (Oph): With Loren and Alan at the Oxbow on a breezy night, crescent moon just setting behind the mountain, and Comet NEOWISE not looking particularly itself (but it was definitely visible here at the Oxbow for the first time). My first planetary of the night is IC 4634 in Ophiuchus, and it’s a very bright little planetary, emphasis on both the bright and the little; it’s not much more than stellar, at least at low magnification. It took considerable magnification to find it, and it’s in an awkward position in terms of chair-height ergonomics. I’m sitting on the ground right now to observe it. But the nebula looks at first glance like an 11th-magnitude star in a field with a fair number of stars of a considerable range of brightnesses; there’s a close pattern of three stars S just barely F and another pattern N-NF the nebula, consisting of a long line of stars arranged in pairs and triangles and the like; that pattern is about 12’ long and runs along the N edge of the field. The nebula is not really very easy to discern as a nebula at this low magnification, and it was only by looking at a photograph of the field that I was able to identify it. It forms a diamond with three considerably fainter stars F and NF it, with the nebula as the P-most vertex of that diamond. N very very slightly P the nebula by 4.67’ is an 11th-magnitude star; S very very slightly F it is the N-most of the pattern of three that I used to find it, and that star is 11th magnitude; due S of it by 1.5’ is a 10th-magnitude star, and from the 10th-magnitude star S slightly F by 0.5’ is a 13th-magnitude star; those make up the pattern of three. It’s very difficult to estimate the actual size of the nebula because I’m sure there is some threshold-level outer nebulosity around it, but it’s mainly stellar at this magnification. With the UHC filter, the nebula’s the brightest object in field, and is larger than stellar, maybe 7” across. There’s still no outer fringe… maybe some will show in the 7mm, although the 14mm still provides a nice view. Swapping in the O-III yields roughly the same effect as the UHC, but reduces the other stars even more, so it leaves no doubt of nebula’s identity; there’s definitely a non-stellar nature to it. Maybe a flicker of a central star at this magnification? With the 7mm Nagler: the seeing is not great down here, but the nebula is unmistakably non-stellar at 225x; there’s just too much power for the seeing. The filters don’t help much in the 7mm, and filtered or not, it’s still hard to determine if there’s a central star.

[Steve Gottlieb]

I've made several observations of IC 4634 in 8" and larger scopes. The first was in 1982 (in a C-8) up to just a month ago, (also 8" aperture) and all revealed a small disc at high power. The central star was visible in my 14.5" and 18" scopes.

8" (6/30/22): at 109x; appears as a a fairly bright blue "star", which is fainter than a mag 10 star 6' S, but slightly brighter than the mag 11 star 4.6' SSE. A narrowband filter turns up the contrast 2-3 mags and it appears significantly brighter than the mag 10 star. Increasing to 176x shows a slightly non-stellar halo and 229x reveals an obvious small disc ~10" diameter. IC 4634 is at the midpoint of the mag 11 star to the south and a similar star to the NNW.

14.5" (7/7/21): at 182x; very bright, compact, high surface brightness disc ~10" diameter. Good but not excellent contrast gain with UHC filter. At 264x; fairly strong blue color, nice small disc. At 352x, the central star was visible in a high surface brightness oval disc, elongated NNW-SSE, ~15"x10". Situated midway between two mag 10.5 stars ~4.5' N and S.

18" (8/19/09): picked up immediately at 225x as a bright, 11th magnitude, very small, bluish disc, ~8" diameter. Responds well to blinking with an OIII filter. At 450x, the high surface brightness 8" disc has an irregular outline and is surrounded by a thin, very faint envelope that increases the diameter to ~12". In moments of better seeing, a very faint central star emerges within the high surface brightness glow. A distinctive right triangle of mag 12-13 stars follows (closest star is 1.3' due east).

18" (7/22/06): picked up at 225x as a bright, small, blue disc of very high surface brightness. Good contrast gain using the UHC filter. Appears much brighter than the similar mag 11 star using the filter. At 435x, the planetary is slightly elongated N-S, ~10"x8" with a strong flash of a central star. There appears to be a much fainter, very thin envelope encasing the high surface brightness disc. Similar view at 565x though the elongation was clearer and the outer envelope increased in size to ~15"x11".

[Uwe Glahn]

I've logged several observation. Best view was from an high altitude place in the Alps with exceptional seeing which allows magnifications of over 800x. I could pick out one of the extensions and the faint CS.

sketch: 27", 837x, no filter, NELM 6m5+, Seeing II
IC4634.jpg
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