NEAT SOUTHERN PLANETARIES : 04
NGC 5844 in Triangulum Australe
This region of the sky is an interesting,
yet often neglected area by amateur observers. It contains
two enigmatic planetaries — one of which has the most
bizarre history. I have divided the surrounding fields into
two main areas of sky. The first area contains various
pretty pairs, a dark nebula and several marvellous
asterisms. Another second selected area is near an
interesting globular and several more pairs.
NGC 5844 / He2-119 / Sa2-115 / Wray 16-168 / ESO
99-1 / PK 317-5.1 / PN G317.1-05.7 (15107-6440) is part of
a small arc of stars in the western portion of Triangulum
Australe. According to most of the modern computer software
that uses the Hubble Guide Star Catalogue, there is on
right on top of the PNe is the bright 7.6 magnitude bluish
star (GSC 9029:2732) that is not at this position. (See
Footnotes 1 & 2.)
NGC 5844 at position 15h 10m 42.0s -64° 41′ 00″
is listed as non-existent, with the PNe He2-119 positioned at 15h 10m
39.9s -64° 40′ 19″. Differences here are merely 52.8
arcsec — so likely that the two objects are really the same. So
let’s assume it is!
To find this planetary, it is best to use the star Triangulum
Australis in the middle of the base of the ‘southern triangle’ and the star η Cir / Eta Circini (15048-6402). Draw
an imaginary line between the two stars. Divide this line by
quarters, and move towards ε TrA
from η. Cir by a whole quarter. This
centres directly on the planetary, where the two 8th magnitude stars
appear within the same field.
NGC 5844’s brightness is 12.1v and
13.2p magnitude and the diameter subtends an angle of 53 arcsec.
AOST2 states that this object is “…70×50 arcsec“, which is partly wrong as even the
photographic image of the inner shell never exceeds 55 arcsec.
Dreyer’s original NGC description
is; “Pb, pl, r, vgvlbm”
— Pretty Bright, Pretty Large, Round, Very Gradual and Very
Little Brighter in Middle. This rather odd description for this
object, as it does not exactly match its telescopic appearance. It
then was subsequently deleted from the revised NGC catalogue and no
reason is given for this deletion. However, this difference has meant
that most Star Atlases and Catalogues — including Sky Atlas
2000.0, Sky Catalogue 2000.0, and in Uranometria
2000.0 [Map 452], etc.; each have not listed this fairly bright
and interesting planetary.
During 1997, at Bowen Mountain, in the Blue Mountains 60 kilmetres
west of Sydney, all observers were surprised at the brightness of
this object, especially as it lies close to the rear-end of
Triangulum Australe and Beta Centauri. Using the 45cm. (18-inch)
telescope there on 23rd August 1997, both Mick McCullagh and Don
Whiteman took sometime to find this object among the brilliantly
starry field of Triangulum Australe. When it was found, it was
clearly obvious. (Even some local visitors looked at this object, but
as first timers I suppose they did not understand the implications of
what they were seeing. However, I did give an explanation the general
nature of planetaries and their evolutions.)
As an ovoid shaped object it is just visible in 15cm., best found
using an O-III filter with medium power. In AOST2, David Frew states
that it can be easily found by blinking across the field an O-III
filter. This is true for 10cm or 15cm telescope, but any larger
aperture can immediately detect its nebulosity. Using an O-III
filter, the brightness is fairly even across the entire disk.
I could also see a slight indentation in the northern edge of the
planetary. Using 30cm, the appearance of this indent becomes more
pronounced, revealing an uneven edge, and this turns into a “bay” in telescopes exceeding 40cm.
Larger telescopes should also start to see some structure in the
planetary — perhaps more obvious using an O-III or Hβ. filter.
Also observers at Bowen,
including Les Sara, thought that the appearance seemed mottled
— and even more so with the O-III. Some faint bipolar features
were also noted, with some difficulty, by each of them.
PNN is invisible in all amateur telescopes and with the stated 16.6
magnitude — this is understandable.
Technical Data on NGC 5844
Little appears in the literature is written about this
object until the beginning of the 1990s. During this time
any observational data available remained scant, but in the
last few years, there has been several studies into this
Older distances often gave around 2.9kpc. (1996), but this has
that has been recently determined by Stanghellini, Shaw &
Villaver (2008) as 1372 parsecs.
Comment : The corresponding lack of data is a
reflection of the poor quality of information on the object’s catalogued position, perhaps more so with
the rejection in the RNGC. Again, the northerners have actually ‘butchered’
this most wonderful object. Yet, if it were in the northern skies, we
probably would never hear the end of it! I do recommend that southern
observers have a look at this object.
If you do so, please correspond with me. If
we can get enough information, we could punish those
northerners by telling them in no uncertain terms what they
are really missing!
- Stanghellini, L., Shaw, R.A., Villaver, E., “The Magellanic cloud calibration of the
Galactic planetary nebula distance scale.”, AJ.,
689, 1942 (2008)
Footnote 1 : Identifying Problems With NGC 5844
The Guide Star Catalogue, designed to be used with the Hubble
Space Telescope, is notorious for having errors with non-existent
stars (c.20%) and misidentifications of known NGC and IC objects.
Most of these have been ‘sifted
out’ by observers like Brian Skiff,
amateurs and professional astronomers by noting differences when
observing objects. Fortunately, most happen to be faint objects.
This 7.6v magnitude bluish star (GSC 9029:2732) stated in
the catalogue proved to be a difficult object to
In the GSC positions, according to the CDS listing of
the catalogued position is 15h 10m 41m 01s −64°
40′ 23.0″. The source of the data is a taken
with the UK Schmidt on March 1976 (Epoch 1976.256) using
III-J emulsion film with an GC395 filter producing the
derived magnitude was 7.61±0.45. Visually, no star
appears at this position nor in several other photographs
of this region. The STsI image also shows no star. No star
in this position is stated in the SAO or any of the
preceding catalogues. Also the positional data of the
centre of the PNe He2-119 and this close 7.61 magnitude
star is 1.1″N and 5″E, and well within the NGC
No asteroids were near this position during 1976 and any
known variable stars. It is not in the New Suspect Variable
(NSV) listing and no known nova is expressed for this
object. It is obvious that a problem exists with this
Some twenty-three references were found during an
Internet search with SIMBAD. Strangely, there is no
reference to the PNN, nor of this star. Nearest star is the
12.51±0.22 magnitude, GSC 9029-1442, whose stated
position is 9″W and 43″S. I could not visually
identify this star either!
At first, it was compelling to think that this star is a
nova or variable associated with the planetary, but after
some checking (and extensive personal searching) a final
reply ended the debate. This was received via e-mail on
Saturday 30 Aug 1997 from Gareth V. Williams the Associate
Director of the IAU Minor Planet Centre at Harvard
University, Cambridge, MA;
“The “star” GSC 9029-2732 is actually an
artefact of the plate measuring process and is simply a measurement
of the ‘center’ of the planetary nebula, NGC 5844. Normally
measurements of non-stellar objects would be so flagged in GSC, but
this object appears to have escaped that classification. I note that
NGC 5844 also appears in the USNO A1.0 catalogue, a list that is
supposed to contain only stellar objects.”
This apparent chaos seem likely because of the presumed
non-existence of NGC 5844. If the catalogues are wrong, then
observers will tend not to place it in their observing programmes.
Although this proved not to be an ‘historical nova’, its final value at least will correct
updates of catalogue listings. It proves that for all the technical
marvels of modern astronomy mistakes still occur.
Interestingly, there remains one puzzling question that still
cannot be explained; How could the magnitude of this ‘star’ be
measured at 7.6 magnitude if the PNe is 12.1v and 13.2p magnitude?
Footnote 2 : Something is Seriously Wrong With
(Title taken from Chapter 31 of Arthur C. Clark’s:
The Lost Worlds of 2001)
This field is strange to about 5° surrounding NGC
5844. Firstly, the SAO catalogue (1966) has some stars
placed in this region, while others, and sometimes brighter
stars are not listed. For example, surrounding the region
of NGC 5844 some other 9.5 magnitude stars are listed.
Using my own versions of Atlas Australis and Uranometria
2000.0, I had some trouble identifying the actual field.
Between the declinations between −64° and
−65°, the SAO is both inaccurate and poorly
A reason for this might be the original data in the
production of catalogues in this region where the problem
seems to have started with the beginning of the
Astrographic Catalogue in the 1880s. Declinations to be
surveyed were delegated to various sites. Those north of
declination −64° were delegated to the Cape
Observatory in South Africa. South of −64° this
was allocated to both Sydney Observatory and Melbourne
Observatory. The Cape Catalogue was used to update
the positions of stars to −64°. Later of the
50,000 stars, some 15% of stars were rejected because no
data on their proper motions were given. In essence,
stellar positions in the declination range of
−52° to −64° have a few stars simply
not listed. When the Astrographic Catalogue was eventually
completed in 1936 — these rejected stars did not make
there way in amateur atlases from the 1950 onwards.
Note: Some additional data used in
the SAO is also taken from Vol.20 of the Ann. Cape.
Obs. Catalogue by Jackson and Stoy. (1950.0)
South of -64°, the details become very confusing. It
does seem that some procedural policies in producing the
southern parts of the catalogue were different than at the
Cape Observatory. Firstly, the magnitude limit is not as
extensive from -64° to the pole. Secondly, it seems
that the first stars, and therefore the oldest positions,
are in the region of declinations −64° to
−66°. Data for these stars in the declination
range were original made using the Third Melbourne
General Catalogue, being reduced without Proper Motion to
the Equinox 1900.0, eventually published by Ellery and
Baracchi in 1917. Again, many stars without known proper
motions were not eventually listed in the SAO.
What this means is that many earlier atlases before this
time are relatively poor when identifying stars. If you own
an old computer program, such as Megastar 4, Voyager 4 or
RedShift 5.0, you will notice the sudden drop off in stars
in the declination range of −64° to
−66°. (Make sure it is SAO orientated data and
not based on the GSC or Guide Star Catalogue.)
Amateurs identifying fields in this region should be
cautious — especially object below about 7th
magnitude. This includes the southern constellations of
Pavo, Triangulum Australe, Circinus, southern Crux,
northern Musca, southern Carina and northern Volans. Soon,
the general introduction of the Hipparcos and Tycho
catalogues to atlases will not have this problem with
identification. This will reduce the uncertainties in this
area to magnitude of about 11.5, but at the moment, no
In regards NGC 5844, I am unsure if it has played a part
to the misidentification of this object. To me, NGC 5844 is
still very likely He2-119 / Sa2-115 / PK317-5.1.
Last Update : 04th November 2011
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