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 4071s 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 nations 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.

He2-68 Small
He2-68 Wide

Fig. 1a. NGC 4071 : Wide Field Colour Image Aladin 12½′×12½′ (left) ;
Fig. 1b. NGC 4071 : Enhanced Small Field Image 40″×40″ (right)

NGC 4071

Fig. 1c. NGC 4071 : Original Graphic in Published Version

NGC 4071 appears is a profusely starry field of stars that lies along Muscas western wing. Although from Sydneys 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.

NGC4071Although 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

NGC4071Discovered 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.

Herschels 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 Nortons still does not list it. It also does not appear listed at all in Burnhams 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 McCullaghs 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. Im 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 Gottliebs 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 Pascolis 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 observers 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

  1. Gorny, S.K., Stasinska, G., Tylenda, R.; Planetary Nebulae Morphologies, Central Star Masses and Nebulae Properties., A&A., 318, 256 (1997)
  2. Kay, Jenny, Southern Cross, June (1998) [Canberra Astronomical Society Inc.]
  3. Ragazzoni, R., et al. 3-D ionization structure (in stereoscopic view) of Planetary Nebulae: the case of NGC 1501, A&A., 369, 1088 (2001)
  4. Pascoli, G., Morphology of Bipolar Planetary Nebulae. I. The Two-dimensional Spectrophotometry. A&A.Sup.Ser., 83, 27 (1990) [As Paper I.]
  5. Pascoli, G., Morphology of Bipolar Planetary Nebulae. II. The Three-dimensional Structures. A&A., 232, 184 (1990) [As Paper II.]
  6. Phillips, J.P., The relation between Zanstra temperature and morphology in planetary nebulae. MNRAS., 344, 501 (2003)
  7. 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′

Thumbprint Nebula in 
Chameleon : Fig. xx
Fig. x. Thumbprint Nebula in Chameleon.
Field Size : 12½′×:12½′.


Last Update : 01st March 2012

Southern Astronomical Delights © (2012)

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