IC 5148 — IC 5150 in Grus

Our sixth part of this series reaches out of the realm of the southern Milky Way. One of the best of the southern objects here is IC 5148 / IC 5150 in Grus, and is a really elegant and terrific annular planetary. I have included, for those that like a tough challenge, and have some aperture, some may like to try to observe the isolated He2-434 (19338-7433), now placed in NSP06a] in southern Pavo.

Unfortunately, during the summer months in the southern hemisphere, roughly between the months of October and March, there are only handfuls of interesting objects to occupy our attention. Observers of planetary nebulae will usually focus most of their attention during this time of year on the Helix Nebula / NGC 7293 (22297-2112) in Aquarius, but there are several other good targets, like the Saturn Nebula / NGC 7009 (21042-1121). In this context, really the Helix Nebula is a southern object, probably much to the chagrin of our northern observing cousins, as the declination is −21°S. However, the Saturn Nebula at −11° declination is equatorial.)

[The link below will bring up a fine sketch of IC 5148 by Rich Jakiel.]

IC 5148 / IC 5150 / ESO 344-5 / PK 002-52.1 / PN G002.7-52.4 (21596-3923) (Grus) was first pinpointed by Sydney amateur Walter Gale in 1894, near the Cranes long neck. For some reason it was not marked in the old Sky Atlas 2000.0 but does appear in the Sky Catalogue 2000.0! The planetary itself is found in its rather desolate field some 1.3°W of λ Gru / Lambda Gruis (22062-3933). It takes at least 15cm. to see its nebulosity, as the total magnitude is 13.0v / 12.9p. Unlike the majority of planetaries, this one is large at about 2 arcmin, as most of the available literature states.

To my eyes the O-III filter image is slightly brighter, but oddly this should not be true, because the observed spectrum is given as continuous. Usually, for any object with continuous spectra has no real advantage when using narrow-band filters.

Observationally, little difference is observed in the apparent size from the CCD or photographic images. A 20cm. clearly reveals its colourless annular structure, including its smallish 25 to 30 arcsec. hole, and consequently, IC 5148 / IC5150 is classified as planetary Type IV or 4. A 30cm. or 40cm. will start to reveal some of the internal diamond-shaped braided structure, as easily seen in the available images, where the eastern side appearing broader and brighter. Contrary to this, AOST1 & AOST2 obscurely states; and a considerable area looks paler (grey), but still luminous.”. This central hole is much smaller than most of the annular type planetaries.

In generally accepted PNe theory, the appearance of central holes are is thought to be due to the strong radiation pressure pushing the surrounding gas away from the white dwarf core, leaving the vacant space. It is likely that the development of annular structures are the sign of the last stages of planetary nebulae formation — just before the nebulous object transforms into its solitary and long-lived white dwarf phase. The planetary shell structure when seen in three-dimensions is probably one spherical shell, if not, two shells, and that we are probably looking directly down upon the poles.

Observations of IC 5148 / 5150

Dennis di Cicco described it as; (S&T., June 1986 p.631);

IC 5148 is a real show piece… With 280× and a UHC-filter, the 24[-inch] in Hawaii showed IC 5148 to be an exquisite giant ring, irregular with a dark centre and a 15.5 central star. Steve Gottieb of Berkeley California, observed it with a 13[-inch] reflector and an O-III filter. He could view the nebula with direct vision and detect the dark centre with averted vision. This object is the same object as IC 5150.

(A nice image taken by him also appears on p.632 in the same issue of S&T.)

Melbournian Southern Observer and imager Neil Avery on 18th September 2006, wrote me this encouraging e-mail on his multi-filter imaging attempts of IC 5148/50 (Figure 3.), which I have reproduced here. He says;

I have imaged one of the PNs that you suggested with my newly acquired Custom Scientific 4.5nm. Hα and OIII filters. Compared with the 13.5 nm Astronomiks I get a further three fold reduction in sky glow. The background sky glow is now so low that there is not a lot to be gained by a dark site. This PN has a fairly low surface brightness but the result is very encouraging. This one is a bit unusual in that the Hα and [OIII] are of comparable intensity giving a fairly neutral colour image. more commonly, H[ydrogen] dominates the outer regions and O[xygen] the inner. Best wishes.

Figure 3. Multi-Colour Image of IC 5148/50 by Neil Avery
Planetary Nebula : Multi-Colour Image by Neal Avery

Description: IC 5148/ PN G002.7-52.4, North 8 oclock, Planetary nebula; VV type 4
Optics : Celestron C11 at f/10. Filters, Custom Scientific 4.5nm. Hα and [O-III]
Mount : Losmandy G11, autoguided.
Camera : SBIG ST8xe at 20°C Inserts Hα and OIII, 9×10 mins., binned 2×2
Processing : L=Hα, G and B= [OIII]
Date: 15 September 2006: Melbourne

Historical Interlude

It is surprising that John Herschel missed this object. Even some of the more modern references, like Burnhams, still do not list this object. As we have seen throughout this series, the common references for southern objects used by amateurs are inordinately incomplete. One of the notable problems with this object is that the IC catalogue gives it as two objects. Most references usually selected it as either IC 5148 or the combined IC 5148/5150. It was given these two different designations by Dreyer (1908) in the Second Index Catalogue (IC).

As mention before, Walter Gale discovered this object in 1894. IC 5148 and IC 5150 differs in position by 11″ in RA and 62″ in Dec. IC 5148s position is taken from observations made by the veteran American observer, Lewis Swift, from an observatory on Echo Mountain near Los Angeles. This planetary is also featured in his list (Mem. RAS., LIX, p.568 (1899)). Swifts positions were taken from images over very wide fields — usually having the general notoriety for having particularly inaccurate positions. IC 5150 refers to the position based on Gales observations. (His catalogue No.3246.) Dreyers Index Catalogue also shows some confusion in the descriptions. Swift states the object is vF, L, lE, *att.”, … very faint, large, little extended, star attached; while Gale states pB, pL, annular” — pretty bright, pretty large and annular. No confirmation was made between the two catalogues numbers, so the current odd designations remain. This discrepancy is slightly unfair on Walter Gale, because his description is closer to the truth (See AOST1), and it is for this reason he lists it as IC 5150. Yet the preferred designation remains as IC 5148.

Technical Data

Professional photography has revealed an outer halo exists that extends the diameter to about 135 arcsec. Radial velocity measurements indicate that the nebulosity is moving towards us by some -23 to -28 km.s-1. Simbad (2011) currently states -26.2 km.s-1. Determined by the faint [O-III] emissions, the nebulosity has an expansion velocity of 53.4km.s-1 — one of the fastest expansion velocities of known PNe. So far, the only adopted distance is 900 pc. (2,900ly) first given by Kingsburgh and English in 1992. Distance by them is stated as an upper limit and is based on the faint Hβ (Hydrogen-Beta) emissions. Due to the faintness of the PNN, determining distances for this object has been difficult. Since originally writing this, Stanghellini, et al. (2008), now state the distance is 1068pc. (Rounded 1070 pc.).

Central Star of IC 5148/50

Visually, the central PNN is at 16.5 magnitude and can possibly be seen in 40cm. or 50cm. telescope, though I have to admit that I have never seen it nor read reports of others. seeing it. It is clearly obvious being central object in images.

According to Weidmann & Gamen (2011), the central star seems to be of an O-type (just like He2-434 [NSP 06a] being found as O-type in the same paper.) REOSC spectrograph attached to the 2.15-m telescope at CASLEO, Argentina Subtracting the nebulae emission, called normalised flux Normalized spectra of O-type CSPN. Absorption lines of HeII are observed in the spectra. The interstellar line of NaI is indicated.

O?. We were able to minimize the nebula contamination and to identify the absorption lines of the Balmer series and HeII 4686Å (the later confirming an O-type spectrum). Méndez 1991 classified this star as hgO(H). Nevertheless IC 5148 does not seem to be an evolved object.

Weidmann & Gamen (2011) also importantly point out in their introduction to this paper, which adds some perspective and poignancy on the developments in the last decade on central stars (CSPN) since NSP 06 was written.

there are about 3000 catalogued PNe in our galaxy, but only 13% of their progenitors have been spectroscopically identified.… The identification of the ionizing star of a PN is not always an easy work; most of them are optically faint objects (low luminosity) and sometimes they are not at the geometric center, because the nebula interacts with the interstellar medium. Also, PNe are concentrated toward the plane and bulge of the Galaxy, where crowding and interstellar dust make difficult to observe and identify they progenitors. The fact that the PNe are easily confused with other types of objects (Frew & Parker 2010) complicates this picture even more, and introduces confusion in statistical works. At present, many non-PNe remain hidden in the catalogs of PNe.

In my view, this planetary is easy to find and is worthy to glance.


  1. Dreyer, J.L.E., Second Index Catalogue of Nebula and Star Clusters, Containing Objects found in the Years 1995 and 1907.Memoirs RAS., LIX Part II (1908)
  2. Stanghellini, L., Shaw, R.A., Villaver, E., The Magellanic cloud calibration of the Galactic planetary nebula distance scale.”, AJ., 689, 1942 (2008)
  3. Weidmann, W.A., Gamen, R., Central Stars of Galactic Planetary Nebulae II : New OB-type and emission-line stars”, A&A., 526, 6 (2010)
  4. [Section: 3.3. Notes of some individual CSPN]


Last Update : 30th November 2011

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