2 Attachment(s)
Object of the Week July 24th, 2022 - IC4634
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.
Attachment 4807
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.
Attachment 4808
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
