NEAT SOUTHERN PLANETARIES : 19
NGC 4071 in Musca
We now return to the far southern constellation of
Musca, which contains a few planetaries and large varieties of
interesting objects, including the first
“really
neat” object in this series the
Spiral Planetary or NGC 5189 (NSP
01). The next best planetary is arguably this one; NGC
4071, which we will discuss in some detail. For some reason I
like this southern object and have always focused on any
information that I stumble upon in my reading of the literature.
Sadly little in the amateur literature appears about the object
— a trait that persistently dogs many southern observers
— much to our detriment I’.
When this was first written back in 1999, little was
known of this object. Now in 2012 little has changed, and it still
remains just as a poorly studied object. Pity!
I have updated some of the observational descriptions,
the some of the distance estimates and made so adjustments here and
there. I have add new references regarding the
NGC 4071’s morphology, updated to
2012.
† Important Note: There was a
significant and mind-numming error by me in the original document
with the location of the Thumbprint Nebula, which I have
inexplicably seemed to have been confused on it is position. I
somehow placed this in the northern constellation of Draco, when in
fact, it is in the far southern constellation of Chameleon. This has
been properly corrected. I have also added this nebula as a new
Surrounding Field objects.
New Update: March 2012.
NGC 4071 / He2-75 / h.3370 / Sa2-82 / Wray 16-104 /
ESO 94-12 / PK 298-4.1 / PN G298-04.8 (12043-6719) [U450] located
some 1.9°NWW (PA 294°) from 4th magnitude red variable
ε Mus / Epsilon Muscae
(12176-6758). Discovered by John Herschel from South Africa during
1838, who thought this object was just a bright nebula, and had no
real inkling that it was a planetary nebula. It was Karl Henize who
revealed its PNe nature, being published in his ground breaking
Southern Hα survey made in 1961 at
Mt. Stromlo Observatory near the
nation’s capital, Canberra.
Although this PN has not been given any proper name, for me it
appears either like a thumbprint or some three-dimensional shape of
one huge intergalactic eye. As the 6′×4′
Thumbprint Nebula that already exists in Chameleon, as DCld
302.6-15.9 / Dark Cloud 303 / BHR 84 / BDN or Bright Dark Nebula
in Chameleon (12446-7848)† [See
Surrounding Fields], so perhaps it is best to just call it the
Eyeball Nebula.
Fig. 1a. NGC 4071 : Wide Field Colour Image Aladin
12½′×12½′ (left) ;
Fig. 1b. NGC 4071 : Enhanced Small Field Image
40″×40″
(right)
Fig. 1c. NGC 4071 : Original Graphic in
Published Version
NGC 4071 appears is a profusely starry field of stars that lies
along Musca’s western wing. Although
from Sydney’s latitude it is
circumpolar, the planetary culminates at 9pm on the 6th May and at
midnight on 22nd March. The telescopic field is marked some
14′NNE of NGC 4071, with a line of four stars in a flat arc,
some 13′ long, and another 9.4 star 20′ further east.
The four stars in a line each have respective magnitudes, north to
south, of 9.3v, 10.0v, 9.3v and 9.2v. Closest of these stars, the
brightest and last star in this list, is given known as HD
104995 / PPM 778794/ CPD -66 1701 (12054-6714). Later values
state visual and blue photometric magnitudes of 9.4V and 10.8B, while
the spectral class lies between B8 and K0III. (Investigating the
surrounding field to 30′ also finds eighteen infrared sources.)
The visually reddish 10th mag star is also the pair DON 1095.
 Although few amateurs, until recently knew of the
existence of the planetary NGC 4071, mainly because it was classed as
a uninteresting gaseous nebula. This wonderful 12.9ph magnitude
elliptical planetary nebula is surprisingly brighter than expected,
but unlike most PNe, its surface brightness is quite low. This may
account for some extreme difficulty in seeing it using high
magnification. This is similar to the problems faced using small
apertures to see the NGC 7293 / Helix Nebula (22297-2050) in
the constellation of Aquarius. Those who are fortunate to own an
Hβ filter, it is likely that it will
be of some use with NGC 4071. As the planetary is classed as a
low-excitation object, considerably gains in contrast certainly will
enhance the faint detail inside the body of the nebulosity. I do not
have one of these filters, so an observation by one or two observers
would be greatly appreciated!
The inner nebulosity is stated as 63 arcsec across, but this
coincides to its small visual appearance of about 40 arcsec. Deep
images extend this to about 80′×51′
Photographically, NGC 4071 displays an unusual dark bar, centrally
bisects the inner parts of the nebulosity. However, this curio is
likely invisible to all amateur telescopes. In 25cm., the entire
nebulosity is just visible to the naked-eye without a filter.
Possibly even 20cm could see the planetary, if the skies were very
dark. I have personally glimpsed NGC 4071 using an
OIII filter in 20cm. under moderately poor seeing
conditions, though I admit is was quite a faint smudge. Using the
OIII filter, the nebulosity literally jumps at you,
and this becomes far more obvious in apertures above 20cm. Telescopes
exceeding 25cm. begin to reveal significant structure, though these
features unfortunately remain colourless and faint. Using the
direct-vision prism was almost useless in 20cm., as most of the
nebulosity was extinguished with significant light loss from the
three prisms.
Observational Descriptions
 Discovered by John Herschel (1847) in 1835 [Sweep 557],
NGC 4071 (h.3374) was simply described on pg.100. as;
“Very faint, round, 40′, has a very
[small] vS star in centre; in a field of at least 80 or 90
stars.”
Herschel’s observation is a bit odd,
as he describes a bright star in the centre to the nebulosity, when
clearly there is no star, but is more towards the southwestern edge.
I could not find any mention of this star in any of the bright
catalogues, including the latest USNO-A2.0, that contains over 526
million sources and is an enormous 3.6Gb in size! All this catalogue
gives is twenty-five stars between 16.0 to 19.5 magnitude, and
all within 1′, but only encompassing the nebulosity. None
appear within it!
Paradoxically, and until very recently, few amateur observational
descriptions exist for this object. The main reason seems to be just
because some common star atlases like Sky Atlas 2000.0 (Edition 1)
and Norton’s still does not list it. It
also does not appear listed at all in
Burnham’s Celestial Handbook. One
exception, however, is Uranometria 2000.0. Oddly, NGC 4071 appears in
the Sky Catalogue 2000.0, though the stated diameter of 75 arcsec
seems a bit too large. This same situation is similar to the presumed
non-existent NGC 5844 (15107-6141) in Triangulum
Australe (NSP 04).
I asked the now late-Scott Mellish to kindly make an observation
for me, which he so gratefully provided, including a small
description and field sketch. (Figure 2) Observed on the 18th
February 1999 from a dark-sky site in the Warrumbungle National Park,
and using fellow ASNSWI member Mick
McCullagh’s 18-inch f/4.5 Dobsonian, he
says of NGC 4071;
“Use of an
[O-III] filter makes a big difference. NGC 4071 has a
couple of stars superimposed across it surface. Using averted vision
I thought it does appear slightly mottled. Overall, this is a nice
soft nebulous smudge.”
The object also does not appear in AOST1. It is likely Hartung did
not include the object at the time, as it was still considered by
most amateurs to be a diffuse nebula. Incidentally, like its big
brother in Musca, NGC 5189 (13335-6559)
(NSP 01). David Frew in AOST2 (pg.292)
says of NGC 4071;
“…It is a
fairly difficult object in 30cm but an O-III filter
makes it comparatively easy. It is about 1′ across, and of
fairly even surface brightness [,] though the preceding edge seems
brighter; a faint field star is superposed on the south edge. D
[distance] is unknown.”
Jenny Kay (1998) says of the PNe;
“12.5″ [f/5
Newtonian] — 50×: Too faint. 105×: There is
uncertainty at this power, barely suspecting that there may be a hint
of a glow at the edge of a very faint 14 mag field star. This star
lies in the east of a small triangle with two others, the star
pattern being a guidepost to locate the planetary. 151×: With
much care and patience, the planetary can be detected as an extremely
faint, relatively large, round glow, with a diameter of 40″.
…[in a] 8″ — This planetary is too faint for me to
detect.”
Kent Wallace from Atascadero, California while observing from
Western Australia (20 February 1998) using a Celestron 8 SCT, says in
a personal communication;
“At 62.5×, [it
is] a good sized diffuse disk requiring the O-III
filter and averted vision. Good response to the O-III
and UHC filters. No response to the
Hβ filter. At 100× can see the
disk with averted vision alone, very faint. At 200×, [I] can see
the disk, but the vision is very
poor.”
Experienced deep-sky observer, Les Dalrymple, in 1999 observed NGC
4071 using his 25cm. (181×, 17′ Field Size) from Engadine,
south of Sydney. He describes, with a noted comment;
“This is a very LBS
[Low Surface Brightness] and fairly faint PNe for these conditions
Only 45 degrees elevation. Appears in a field which is littered with
faint [star]s. To the NE by 7′ is a mag 9 [star]. Appears
basically as a translucent disc with an indefinite central hole.
Using AV [averted vision] it occasionally seems annular. In the SW
corner of the halo it seems there is an enhancement in the form of a
slightly brighter curved streak tracing inside the outline of the
outer halo. This enhancement is only slightly brighter than the
balance. 90″−100″ diameter. No central [star]
visible. Not seen without the
filter.”
“Note. The
filter was a Lumicon UHC (narrowband) which passes both doubly
ionised Oxygen and Hydrogen-Beta lines.
I’m trying to remember who put me on to
this one because it is rarely found in most of the main-stream
atlases. From memory, I believe it is the faintest integrated
magnitude PNe in the whole NGC (please correct me if you know better)
— not absolutely certain on that
one”.
In Steve Gottlieb’s in his detailed
“NGC
Notes”, observed on 6th July 2005 in
45cm (18-inch) at the Magellan Observatory in Australia;
“I had a difficult
time ferreting out this faint PN that is buried within a very rich
Milky Way field. It was finally picked up at 76× (27 Panoptic)
and OIII filter as a faint, round disc at least
40′ in diameter. Removing the filter, a faint star is
superimposed on the SW side of a low surface brightness glow. Also
viewed unfiltered at 228× which showed the faint star and the
disc more easily, though this is quite a faint NGC planetary. The
best view was at 128× using an OIII filter. The
disc appeared fairly faint with subtle irregularities in surface
brightness and was likely brighter along portions of the
rim”.
Looking at the photographic image I think finds some similarity to
NGC 6445 (17493-2001) in Sagittarius (Unpublished NSP 21).
Here the symmetrical structure appears as two bright illuminated
“bookends” along the north and
south parts of nebulosity. More specifically, both NGC 4071 and NGC
6445 share the “new” and rarer
form of PNe known as bipolar planetary nebulae or abbreviated BPNe.
About forty-five BPNe are now listed as such.
NGC 4071 Catalogue Data
Like many southern objects, the absolute position is partly
uncertain. Brian Skiff states that the true position is 12h 04m 15.3s
−67° 18′ 35″, which Acker and Milne determined
in 1982. This position also appears in the Strasbourg-ESO PNe
Catalogue. I have attached Figure 3, which is a finder chart for
NGC 4071, and includes several objects already mentioned in the
text.
Data in the Strasbourg-ESO Catalogue (1992) finds the
expansion velocity of the visual part of the envelope as +14.1
km.s-1 (1984), though later data suggests a slightly
larger +15.2 km.s-1, and the radial velocity is
+11.0±3 km.s-1 (1983) away from the Sun. In 1971,
the largest diameter was measured as 63 arcsec. Electron densities
(Ne of the visible nebulosity shows weak densities of
NeII, [OIII]=620±60 and
[SII]=410±50, which also explains the visual
telescopic elusiveness of this planetary. Until the mid-1990s, no
observations by were obtained in NIR, IRAS, RADIO or IUE for this
object. Most significantly, when it was alluding that this PNe had
strange structures, the ESO took a monochrome image, with its
2.2-metre telescope, by Baessgen and Bremer in 1988, later appearing
in paper by Meatheringham, Wood and Faulkner (1989)
The line intensities of the PNe are as follows;
Hβ=100, HeII=63,
[OIII]=786, Hα=294,
NII=259, SII=30 and
SII=24. The data here shows the strength of the
[O-III] line is quite high compared to
Hβ
([OIII]/Hβ]. (See
Postscript.) This indicates ratios almost equivalent in
standard PNe, except with the unusual excesses of Nitrogen and
Sulphur — the primary precursor to BPNe. Over all the intensity
is below par, and this account for the difficulties in seeing this in
the telescope.
Most significant of later observations during the 1990s was the
multi-wavelength imaging taken by the European Southern
Observatory (ESO) in Chile. The individual wavelengths
(Hα, HeI,
OIII, NII.) These images (Figure 4)
have been adopted from the Innsbruck PNe Database, which was taken
from the observations of C.Y. Zhang on 1st July 1996. This may also
be found alternatively at the site of the Innsbruck PNe Database.
Looking at the previously mentioned line intensities, the
distribution becomes light in the main emission wavelengths becomes
quite apparent. For example, one of the most interesting things is
the dark bar of NGC 4071. Composition of this feature is stronger in
Hα and NII, while the
contribution from the HeI and OIII is
minor. Another is the distribution of the HeI image,
which concentrates the energies to the inner part of the expanding
nebulosity. Compare this image with the Figure 5, showing the
combined light image, and also compare the individual wavelength
images to theoretical one.
Distance, Size and Age of NGC 4071
For some time, distance to NGC 4071 was estimated at 1.3kpc.,
though even earlier observations suggests more like 1.8kpc. This
result matches the so-called Shklovskii distance. Using the
various distance methods available, the unreliable statistical
distances against all known PNe, range anywhere between 0.8kpc. and
1.4kpc. SSV (2008) determines distance as 1.60 kpc. (1.596
kpc.)
Gorny, Stasinska & Tylenda (1997) state the diameter of 0.56pc.
or 1.7ly., making it among the among largest of known PNe. SSV (2008)
use the radius if nebulas ionisation front
as 31.5 arcsec, scaling the true diameter as xx.x pc. Nebula flux at
5 GHz is a very low 0.026, making this a low excitation planetary.
Age is currently estimated to be around 15,900 years.
General Nature of NGC 4071
Much has been investigated with NGC 4071 in recent decades,
especially in understanding its morphology.
The first of the significant papers appeared in the 1990s by
Pascoli (1990) [Paper II], who concluded that NGC 4071 is a possible
bipolar planetary (BPNe), and ranks among the Helix, Ring Nebula
(M57) and NGC 2440. However, its characteristics seemed to match the
Mz 1 / Menzel 1 / He2-130 (15302-5859) in Norma, discovered by
Donald Menzel in 1922. Pascoli comments on his observations of NGC
4071, whose statements can be verified by looking at Figure 5. His
words gives some factuality to the nature of the BPNe. He says;
“NGC 4071 presents a
very contorted aspect with ansae which seems to be pair related to
two symmetric bright condensations. The two central ansae are nearly
parallel and straight, the outer ones are curvilinear and seem
delineated as a faint polar nebulosity. One finds a similar
morphology with Mz 1 / He2-130 …Comparison with other
bipolar nebulae such as NGC 7293 [and] NGC 6720 is
interesting.”
Figure 5 clearly and easily shows the two bright condensations,
that are nearly equal in brightness. (Figure 10 in the
Pascoli’s paper). The two condensations
are joined by dark bar intersecting the nebulosity. Pascoli
inspection of the Hα images that
were available to him clearly show these features.
Pascoli followed his first paper with an intricate analysis
that includes computer modelling in Pascoli (1990) [Paper II.]
Although the mathematical analysis and theoretical internal
structures are quite complex, the resultant map confirms much of NGC
4071, and other BPNe / PNe structures. Here he describes NGC 4071
as “late
elliptical”, whose expected
orientation, between the main central axis and the line of sight, to
be tilted by about 65°. The mean structural radius is given as
0.291 pc. or 0.95ly. with an expansion velocity of 15.2
km.s-1.
Without getting into too much complexity, the structures drawn in
Figure 5 does look similar to Figure 2. Three images are displayed,
the plan and end elevation, showing the generalised structure of the
observed nature of NGC 4071. The later manipulation uses the general
formulae from this paper, accounting for its general spatial
orientated.
According to Ragazzoni, et al. (2001) compares NGC 4071 (and other
PNe) to NGC 1501, explaining the morphology has;
“The optical
appearance… mainly depends on the
“latitude”,
I.e. on the angle of view of the dense, inhomogeneous equatorial
belt: at “low
latitudes” (from (0,135) to
(0,15)…) it is a broad disk presenting inner, amorphous
structures. When seen almost pole-on (from (0,60) to (0,105)), a
sharp, oval ring appears, brighter along the minor axis
(corresponding to the projection of the c axis of the
ellipsoid).”.
“A quick look through
the main imagery catalogues indicates that NGC 1501-rebuilt resembles
M 3-30 when seen from (0,15), A 53 and NGC 7094
from (0,30), IC 1454 from (0,45), A 73 from (0,60),
A 70 from (0,105), NGC 4071
from (0,120) and NGC 6894 from
(0,135).”
The numbers in brackets are the estimated angle (in
degrees) of the central main axis of the planetary from the
observer”s point of view.
PNN of NGC 4071
Overall, the amount information about the PNN in Strasbourg-ESO
Catalogue and other references is particularly poor. For example, the
stated 19.2v mag and 18.20 B.mag — and these are likely both
uncertain by more than 0.5 magnitudes. SIMBAD suggests that the
central star is 16.11 magnitude, but the spectral class is still
remains uncertain. Studies by Gorny, Stasinska & Tylenda (1997)
suggests the mass of the PNN may be between 0.698⊙ and
0.839⊙, while the Zanstra temperature is 151,000K, and by
calculating the size of the PNN, the energy is some
ninety-five times more luminous that the Sun. Phillips (2003)
gives the Zanstra temperatures as TZ(HeI) =
141,700±83,00K or TZ(HeI) =
118,000±10,600K.
NGC 4071 has proven to be almost unique, and some of its nature
will likely be revealed in this century. As of March 2012, no HST
image exists nor is presently planned.
References to NGC 4071
- Gorny, S.K., Stasinska, G., Tylenda, R.;
“Planetary Nebulae Morphologies,
Central Star Masses and Nebulae
Properties.”, A&A.,
318, 256 (1997)
- Kay, Jenny, “Southern
Cross“, June (1998) [Canberra
Astronomical Society Inc.]
- Ragazzoni, R., et al.
“3-D
ionization structure (in stereoscopic view) of Planetary Nebulae: the
case of NGC 1501”,
A&A., 369, 1088 (2001)
- Pascoli, G., “Morphology of
Bipolar Planetary Nebulae. I. The Two-dimensional
Spectrophotometry.”
A&A.Sup.Ser., 83, 27 (1990) [As Paper I.]
- Pascoli, G., “Morphology of
Bipolar Planetary Nebulae. II. The Three-dimensional
Structures.” A&A.,
232, 184 (1990) [As Paper II.]
- Phillips, J.P., “The relation
between Zanstra temperature and morphology in planetary nebulae.
MNRAS., 344, 501 (2003)
- Stanghellini, L., Shaw, R.A., Villaver, E.,
“The Magellanic Cloud Calibration of
the Galactic Planetary Nebula Distance
Scale.”, AJ., 689,
194 (2008)
Ancillary Object
DCld 302.6-15.9 / Dark Cloud 303 / BHR 84 / BDN or Bright
Dark Nebula in Chameleon / Thumbprint Nebula (12446-7848) is placed
in the far southern constellation of Chameleon and is just 11°
for the south celestial pole. This dark nebula has the size of
roughly 6′×4′
Fig. x. Thumbprint Nebula in Chameleon.
Field Size : 12½′×:12½′.
Last Update : 01st March 2012
Southern Astronomical Delights ©
(2012)
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