IC 2149 in Auriga

December 2025 - Nebula and Cluster of the Month

As the year draws to its close, I’m going to indulge myself. I make no apologies for this. You never know, I may even make one or two converts. For a long time, I have been a keen seeker of the tiny planetary nebulae, those objects usually ignored by visual observers. Why are they ignored? Because they’re very small, often indistinguishable from stars and they’re not ‘exciting’. They’re not ‘interesting’, not ‘spectacular’. My argument is that they are exciting, they are interesting and they are spectacular.

This month we’re going to look at IC 2149, a ‘stellar’ (though it’s not stellar) planetary nebula in Auriga, riding high in the December skies.

IC 2149 was discovered photographically by Williamina Fleming, a Scottish astronomer working at Harvard College Observatory, in 1906, and it entered the second Index Catalogue in 1908. The description is typically terse: Planetary, stellar.

Multiwavelength studies of IC 2149 reveal that it does not comfortably fit a simple planetary nebula profile, but shows considerable asymmetry. Optical and radio images reveal an asymmetric object, yet with some bilateral symmetry, with a very bright, compact inner zone surrounded by fainter, more diffuse emission.1

High-resolution imaging by the Hubble Space Telescope shows a bright knot, irregular shell structures and a tenuous outer halo, all indicating a history of directionally irregular mass loss.2,3

A colour composite image of planetary nebula IC 2149 in Auriga captured by the Hubble Space Telescope with its WFPC2 instrument courtesy of the Hubble Legacy Archive.
A colour composite image of planetary nebula IC 2149 in Auriga captured by the Hubble Space Telescope with its WFPC2 instrument courtesy of the Hubble Legacy Archive.

Distance estimates place IC 2149 at approximately 1.0—1.2 kpc (3200—3900 light-years) from the Sun4. At this distance, the ionised mass is small, around 0.03 solar masses, consistent with a low-mass progenitor at the end of its Asymptotic Giant Branch phase. Expansion velocities measured from optical spectroscopy show moderate values of a few tens of km/s.5,6 Radio continuum mapping reveals further structural complexity.7

The central star is a hot O-type star showing strong stellar wind signatures. Ultraviolet and optical spectroscopy reveal iron-group lines and P Cygni profiles, indicating ongoing mass loss.8

Visually, it could be argued that IC 2149 is not much to look at. If you’d indulge me, though, I’m going to ask you to search for IC 2149 visually at low to moderate power. At magnitude 10.6, it should be clearly visible, if not immediately recognisable. In discussion with other visual observers, I’ve noticed that some (not all) can spot a ‘stellar’ planetary nebula almost immediately, even if the magnification does not allow a glimpse of its extended shape.

To find the object, centre your field on β Aurigae (magnitude 1.9), on Auriga’s right shoulder. Move one degree north to the reddish, 4.3-magnitude π Aur, then just 38’ slightly north of west from π. IC 2149 should now be close to the centre of your field. I, and others, find that there is something about a planetary nebula that makes it stand out. There’s a certain quality of the light that makes it different, somehow, from the field stars. Maybe it’s because the light from a planetary nebula is not a continuum. I don’t know, and I’m sorry for being vague, but try it for yourself. For me, IC 2149 pops out almost instantly, even on lower finding powers.

Once you think you’ve got it, swap your eyepiece for a higher magnification one, and the extended nature of the object should become clear. Failing that, ‘blinking’ with an OIII or UHC filter should make the object obvious.

I’ve included an observation I made of IC 2149 back in 2013. On that occasion, I recorded that elongation was suspected at x150, and this was confirmed at x450. The middle is brighter and there is a fainter outer periphery. The object is tiny, and no further detail was visible.

A sketch of planetary nebula IC 2149 in Auriga by Patrick Maloney through his 12-inch newtonian telescope at x150 magnification.
A sketch of planetary nebula IC 2149 in Auriga by Patrick Maloney through his 12-inch newtonian telescope at x150 magnification.

May I take this opportunity to wish you a very happy Christmas season (or whichever other Midwinter celebration you choose to celebrate).

Patrick Maloney

Object RA Dec Type Magnitude
IC 2149 05h 56m 24s +46° 06’ Planetary nebula 10.6

References:

  1. Vázquez, R. et al., 2002. ‘Multiwavelength observations of the peculiar planetary nebula IC 2149’. Astrophysical Journal, 576, pp.860–870.
  2. ibid
  3. Miranda, L.F. et al., 2000. ‘High-resolution observations of bipolar planetary nebulae’. Monthly Notices of the Royal Astronomical Society, 311, 748–760.
  4. as 1.
  5. Perinotto M. (1982). ‘Stellar wind in the nucleus of IC 2149’. Astronomy & Astrophysics, 108, 314.
  6. Sistla, G., 1977. ‘Extinction and radio structure of IC 2149’. Monthly Notices of the Royal Astronomical Society, 178, pp.325–334.
  7. ibid
  8. Feibelman, W.A., 1994. ‘Spectrum of IC 2149 and its central star’. Astrophysical Journal, 426, pp.653–665.

If you'd like to try out the Clear Skies Observing Guides (CSOG), you can download observing guide for the current Cluster of the Month without the need to register. CSOG are not associated with the Webb Deep-Sky Society but the work of Victor van Wulfen.