3 Attachment(s)
Object of the Week February 6th 2022 - NGC 2242
NGC 2242
Other Names PN G170.3+15.8
Planetary Nebula
Constellation Auriga
RA: 06h 34.127m
Dec: +44° 46.62'
Mag: 15.1 (P)
Size: 22.0"
Mag C. Star: 17.6
When we think of planetary nebulae in Auriga we tend to think of IC 2149 but many observers are
unaware of the fact that there is also an NGC planetary in the constellation. When Lewis Swift
discovered NGC 2242 in 1886 using the 16” refractor at the Warner observatory in Rochester,
New York he could not have realised that he had found the last planetary nebula to be added
into the NGC. Having said that for most of the time since its discovery NGC 2242 has been
thought to be a galaxy, and indeed Zwicky catalogued it as such in the CGCG. it was not until
1987 that it was examined and found to be a planetary nebula, albeit a rather faint one, although
Sulentic and Tifft had suggested it might be a PN in 1973 in the RNGC.
Attachment 4603
The planetary is thought to be about 6500 light years away and about 1500 light years above
the galactic plane. It is probably one of only a handful of halo PN known. In age terms
NGC 2242 is thought to be very old. The morphology of the planetary is somewhat
reminiscent of the much brighter NGC 7662 with an inner ring and halo, at least on the
SDSS image.
Attachment 4605
The central star is very hot with a modelled temperature of around
137000K so most of its light output will be in the UV. Its spectral type is given as
O(H). This has translated to a very high nebular temperature of perhaps 25000K.
NGC 2242’s late re-classification as a planetary nebula is probably why it has not
appeared in any of the main observing guides. There also appears to be some confusion
over how best to observe it. Steve Gottlieb suggested that when using his 17.5” it did
not respond well to filters however, Kent Wallace in his monumental guide on visual
observations of planetary nebulae using a 20” (50cm) suggests that it does respond
to both UHC and OIII filters so it maybe that you need a larger telescope to get a filter
effect. There are no reports that it responds to an H-Beta filter. Its spectra shows quite
strong OIII and H-beta lines so it should really respond to those filters. NGC 2242 is
probably one of the faintest, if not the faintest, planetary nebulae in the NGC so it may
require significant apertures to find, possibly in the range 40 cm at up. Swift described
the object at discovery as exceedingly faint and very small and round. I suspect that to
see much more than a faint circular patch is going to require a telescope in the 50cm+
class and probably better skies than we have in the UK. I suspect that because of its
size that a high power is probably going to be required to find it, which may also be part
of the reasons that filters do not work so well. The central star is going to be much too faint
to see at around 18th magnitude. The Interstellarum Field Guide suggests that it is an
object for larger telescopes although I guess that observers from high altitude may see
it with smaller ones.
Attachment 4604
Image of NGC 2242 by Ian Smith
And as always,
Give it a go and let us know! Good luck and great viewing!
