N79 & N83 Complexes in LMC

A Visual Observation of Interesting Structures in the Large Magellanic Cloud. Researchers Say one of Them Could be a Rival of 30 Doradus Nebula

Figure 1. The Complexes under observation

Early March, it is dark enough now (around astronomical twilight), so the Large Magellanic Cloud looks amazing, high in the southern sky. I am ready to aim the telescope (8-inch in diameter) to the west region of this galaxy, where the arm W is situated, to find and observe in detail other interesting complexes of our nearby galaxy (i.e. LHa120¹-N79 and N83). The extent of these regions are outlined in Fig. 1b in the paper "Ultraviolet and Optical Observations of OB Associations and Field Stars in the Southern Region of the Large Magellanic Cloud", Joel WM. Parker  et al. (2000). In the 1° field of view (Figure 1) the white-blue star HD 31518 (magnitude 7.2) is the brightest one. Near the center, LHa120-N79 is visible along with its companion LHa120-N83, both are small regions of nebulosity with N79 appearing more prominent and "wide". These complexes reside in a bigger structure named Shapley VII, one of the giant stellar and gaseous groupings of the LMC that has an angular dimension of 48x25 arc min (PA 90°). Shapley VII lies in an even bigger structure named SGS² 7 that has an angular dimension of 55x55 arc min. In the field of view, toward the East of these complexes, a region showing a higher concentration of very faint stars embedded in subtle nebulosity, elongated East-West, can be detected. We are talking about LHa120-N94 which includes the OB association³ LH⁴8, which encloses, in turn, the cluster of stars NGC 1767, discovered by John Herschel. A few brighter stars are superimposed in that region. This region seems to be connected to the two main nebulosities by very subtle nebulosity.

N79 is an irregular HII region, roughly 17x14 arc min in size, that contain the OB associations LH1 (also NGC 1712) and LH2. Its coordinates are R.A. 04h 52m 00s Dec. -69° 22` 30" (J2000.0). This region has a star formation efficiency exceeding that of 30 Doradus by a factor of ∼ 2 as measured over the past 0.5 Myr. The first observation of this object was made at low magnification (42x). The animation below showing the N79 complex (Figure 2) was made using a DSS image to show what I think it could be nicknamed the "Magellanic Horsehead Nebula" because it resembles, in my opinion, the profile of a horse. That section of the complex is called LHa120-N79E and is the most prominent one (see Figure 4), appearing as a rather elongated nebulosity E-W. Using averted vision the nature (as a nebula) of this object is more obvious, appearing somewhat wider and more contrasted. Some of very subtle nebulosity seems to lie in a small area southwest of LHa120-N79E. Higher magnification and nebular filters will surely help for a more detailed description of this area.

Figure 2. Zoom in  into LHa120-N79, a complex in LMC.

Using the same magnification we move to the complex N83, situated about 15 arc min northeast of N79.  Henize (1956) identified four ionized gas regions lying in that direction (N83A, B, C, D). Lucke & Hodge (1970) detected an OB association (LH 5) spanning over 16 square minutes (3600 square pc) around N83. It contains 26 blue stars (Lucke 1974) the brightest of which is Sk-69◦30 (Sanduleak 1970), a G5 Ia with a visual magnitude of 10.18 so it is the easiest star to see of three that are visible there (see paper "HST study of the LMC compact star-forming region N83B" by M. Heydari-Malayeri et al.). Another one of the three stars looks like a small roundish nebulosity where a star is visible within it when using averted vision. Actually, that star, Sk -69 25, is the main exciting object of the mentioned nebulosity which is known as N83A, also NGC 1743 (seeFigure 6). 

At the same magnification a nebular filter, like UHC, improves the view of both complexes. N79E is visible, with averted vision, as a rather elongated nebulosity where a couple of stars are glimpsed for moments. With a similar configuration of that in N83 complex, three stars can be detected in the N79 area, to the south of N79E. One of them looks actually like a star embedded in a small and round nebulosity, this object is MCELS⁶-L25 (see Figure 4), while the other ones are the 10.7 magnitude blue supergiant HD 268718 and the 8.5 magnitude HD 31722. The whole area seems to be engulfed by very subtle nebulosity. 

Back in N83, the component N83A looks like a small nebulosity while the entire star-forming region seems to be engulfed by some nebulosity also.

Figure 3. The object H72.97-69.39.

Picture courtesy of Bram B. Ochsendorf.

Taken from the paper "The Star Forming

Complex N79 as a Future Rival of 30 Doradus" 

written by him and his team and included here

with his permission. 

The so-called high excitation blob⁵ N83B (also NGC 1748) which lies about 2.5 arc minutes north-east of N83A (Figure 6), and is around 25 light years in diameter, probably represents the most recent massive starburst in the giant HII complex N83 and the OB association LH 5. Heydari-Malayeri et al. (1990) discovered a compact HII region toward N83B. This object, which they named N83B-1, turned out to be a member of the so-called high-excitation blobs (HEBs) in the Magellanic Clouds. The brightest blob is the compact HII region N83B-1.

The zone of LH8 shows, through a UHC filter, smooth nebulosity, being more obvious toward the edge of the eyepiece field and less visible (maybe absent at all) in the zone between it and the complexes under study.

Now, a view of MCELS-L25, situated close to the 11.8 magnitude star RMC 54F (according to SIMBAD Database), with higher magnification (78x), shows a very small and detached hazy patch that looks brighter toward its center. N79E looks like an elongated structure where some stars, members of the OB association LH2 (NGC 1727), are embedded and associated with the nebulosity. Averted vision improves the view of this section.

Through this eyepiece, giving 78x, only N83A appears like a roundish object, compact, and with a hazy appearance. Some of nebulosity is hard to detect in the area where the object MCELS-L55 lies. 

Applying a UHC filter, the view of N79 and, in particular, N79E is very interesting. N79E is, by far, the most prominent feature there, where faint stars member of LH2 can be glimpsed using averted vision. For moments, and of course using averted vision again, the component N79D can be barely seen, very faint and round in shape. The star cluster KMHK 187 is associated with this nebulosity according to SIMBAD Database. MCELS-L25, through this magnification and filter, looks like a small hazy spot with a star-like brightness at the center.


H72.97-69.39, a precursor to the R136 cluster in 30 Doradus? 

At the heart of the large-scale complex N79 lies an extremely luminous object which immediately draws parallels to the central cluster of 30 Dor, R136 (Nayak et al.) (See Figure 3). Bram B. Ochsendorf and his team refer to it as ‘H72.97-69.39’ (I indicate it with red letters in Figure 4). This object is more luminous than any MYSO⁷ or compact H II region discovered with large-scale IR surveys of the LMC and Milky Way (read more in the paper "The star-forming complex LMC-N79 as a future rival to 30 Doradus" by Bram B. Ochsendorf et al. 2017). So, if you observe this region of the Large Magellanic Cloud with your telescope, remember that a peculiar and intriguing object resides there.

Figure 4. LHa120-N79 components

At this magnification (78x) and UHC filter, N83A is clearly visible being the most conspicuous feature (in brightness) of the whole complexes. It looks, as with lower magnification, like a round and small nebulosity with its star at the center. A very challenging object, difficult to see, is MCELS-L55, appearing like a ghostly round patch using averted vision.

There is a good view of the nebulosity in N79E using the Orion Ultrablock filter. Through this filter the stars associated look a little more clear. N79D is an elusive object and it could not be clearly visible at this magnification and this filter. On the other hand, MCELS-L25 appears like a small patch of nebulosity close to the 11.8 magnitude star RMC 54F.

In the complex N83, N83A is visible with not difficulty appearing more bright and nebulous than its counterpart in N79 complex. N83A reminds me a kind of small and bright planetary nebula. MCELS L-55 is elusive and a challenging object through this filter also. It seems to show up very briefly but I can not assure it is visible. It is, without a doubt, a good test for rods in your eye.

Using higher magnification...

Figure 5. N83B detailed image
Credit: M Heydari-Malareri & NASA/ESA.

106x is a good magnification to see the whole structure in the field containing the two complexes under study. Now the association LH2 and the associated nebulosity is visible in more detail. The star CTIO85 263 (visual magnitude 12.4 according to SIMBAD Database), is the brightest one visible in that association through an 8-inch telescope (indicated with an arrow in Figure 4). N79D is barely detected using averted vision, appearing seemingly round in shape. At this power, N83A looks now like a small and compact stellar cluster.

Through a UHC filter N79E looks faint, hazy, and without stars. The nearby structure N79D can be detected using averted vision but still elusive, faint, and challenging. It appears like a round structure separate from N79E by no nebulosity.

N83A looks bright, nebulous, and rather round in shape.

Figure 5 is a composite image of the region N83B taken by HST/WFPC2. The brightest blob is the compact HII region N83B-1 and the fainter one below it (∼100 in size) is N83B-2. The small arc-nebula further south, centered on a relatively bright star, is N83B-3.

Figure 6. LHa120-N83 components

A final observation of the complexes using 166x allowed me to see even more details. The component of N79, MCELS L-25, seems to be composed by two "star-like" objects, like two slightly defocused stars. N79E is visible with more detail, showing several stars embedded in faint elongated nebulosity. N79D is again visible, round, faint, and displaying smooth brightness. Averted vision is necessary.

N83A is clearly visible showing some faint nebulosity in its outer part. The section named MCELS L-55 is hard to see, challenging and faint. A few stars seem to be glimpsed embedded in extremely faint nebulosity.

Orion Ultrablock filter and averted vision make it possible to see two objects associated with nebulosity in MCELS L25. The view of N79D through this filter seems to get worse with respect to that obtained without any filter.

Another stunning formation in our satellite galaxy awaits to be seen by observers with telescopes during a clear night in the southern hemisphere summer.

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1_  LHa-120 N- This is the full name of an entry in the Henize catalogue of LMC emission nebulae. "L" refers to the Lamont-Hussey Observatory of the University of Michigan; "Ha" means the Hydrogen-alpha emission line, the key signature line used in the survey; "120" refers to the plate number (objective prism plate) for the LMC; "N" labels the object as a nebula, as distinct from a star (label "S").

2_ SGS are the supergiant shells, the largest of complex filamentary structures in irregular and spiral galaxies, indicative of a violent ISM, with diameters approaching 1 kpc (Goudis & Meaburn 1978). SGSs are thought to be formed by the fast stellar winds and supernova explosions of multiple OB associations.

3_ OB Association: The concept of a stellar association was originally introduced in 1949 by V. A. Ambartsumian, who later separated them into OB and T associations (Ambartsumian 1968). Morgan, Sharpless, & Osterbrock (1952) considered as a stellar association any loose group of stars within an area where bright OB stars exist and with evidence of a common origin.

A recent definition of a stellar association (Kontizas et al. 1999) refers to it as a single, unbound concentration of early-type luminous stars, embedded in a very young star forming region.

4_  LH is a catalogue of OB associations in the Large Magellanic Cloud compiled by Lucke & Hodge.

5_ The compact HII regions called High-Excitation Blobs (HEB) constitute a rare class of ionized nebulae in the Magellanic Clouds. They are characterized by high excitation, small size, high density, and large extinction compared to typical Magellanic Cloud HII regions. These objects are tightly linked to the early stages of massive star formation.

6_ MCELS means "Magellanic Cloud Emission Line Survey". This is a joint project of Cerro Tololo Inter-American Observatory (Chile) and the University of Michigan using the CTIO Curtis/Schmidt Telescope.

7_ MYSOs stands for Massive (>8 Msolar ) young stellar objects.

The Aggregate Shapley I in LMC

Nebulae and stellar associations reside in this complex in the central region of the Large Magellanic Cloud. How much can we see through an amateur telescope?

It is Spring in the Southern Hemisphere, so it is time to aim a telescope to one of our satellite galaxies, the Large Magellanic Cloud (hereafter LMC), and find another interesting structure there. The Magellanic Clouds show a large variety of bubbles, superbubbles and supergiant shells among its objects, many of them being visible for the amateur observers with common telescopes.

"McKibben and Shapley (1953) were the first to distinguish the giant stellar and gaseous groupings of the LMC, the well known Shapley constellations I - V. Later, van den Bergh named (in 1981) the constellations VI - IX. These seem to be the most active star forming areas of the LMC" (paper "Morphology and Stellar Content of Complexes in the Large Magellanic Cloud" M. Kontizas et al. 1995).

This video by ESO`s VLT is a zoom-in view of the interesting group of nebulae and OB stars  named LHa120¹ N44, one of the targets you can observe with an 8-inch telescope.

This article deals with this complex which is also known as "Shapley Constellation I"  according to the LMC extended catalogue (Bica+ 1999) published in VizieR web page. N44, cataloged by Henize (1956) and named DEM² 150, 151 and 152 by Davies et al. (1976) is a luminous HII complex in LMC. It contains an assortment of compact HII regions, filaments, and shells of all sizes, as well as three OB associations³, LH⁴47, 48, and 49 (Lucke & Hodge 1970). N44 is dominated by a prominent shell around LH47 in the central region (Chu & Mac Low 1990), paper "The Multi-Phase Medium in the Interstellar Complex N44" by Sungeun Kim et. al. 1998. Situated at RA 05 22 06.9 Dec -67 56 46, N44 lies (see Figure 1) about 43 arc minutes southwest of a curious structure named "Sextant" (see the article "An enigmatic Structure in the Local Universe - part 2" in this blog). 

The observation was made from Uspallata valley, in Los Andes mountains, where the dark skies make possible to carry out this kind of projects. 

Figure 1. Position of the complex N44 in LMC. North is up.

Two main hazy regions are visible in the field of view at a first observation at 48x. I call them "northern region" and "southern region" (see Figure 4). The northern region is bigger than the other one but both look pretty similar in the sense that they show several faint stars embedded in nebulae structures. I identified this complex after recognize the T-shaped asterism formed by the stars HD 35862, GSC-9162-0453, HD 35978, and GSC-9162-0321 (visual magnitudes 9.3, 11.4, 9.7, and 11.4 respectively). The brightest star in the field of view is the 8.5 magnitude HD 35665. According with data given by the aforementioned catalogue (Bica 1999) the center of Shapley Constellation I lies at the center of the bigger region (indicated with the blue arrow in Figure 4). This aggregate has an overall dimension of 23 x 16 arc min and an angular position of 150° according with the same source (See Figure 2).

Matching with what can see on the DSS image (Figure 4), the area labelled with an ellipse is where nebulosity and stars are visible at this power. That is the area of the association LH49 and the HII region IC 2128 (also N44D). I found discrepances about the nature of IC 2128. Some sources (e.g. SIMBAD Database) state that is an HII region while others (like the revised NGC/IC catalogue and STScI DSS) say it is a stellar association. Beyond that differences, it is not a conspicuous object at all. The section easier to detect (a little better using of course averted vision) is the more contrasted patch on DSS image in Figure 4 immediately southwest of the 9.7 magnitude star HD 35978, appearing as a faint and defocused star engulfed, in turn, by very subtle nebulosity. Averted vision is necessary to get this view through an 8-inch telescope at low magnification. 

Figure 2. According with the LMC extended catalogue (Bica 1999)

Shapley constellation I is a 23x16 arc minutes wide structure with

an angular position of 150 degrees. North is up. East to the left.

Moving to the northern section of the complex, N44C (also NGC 1936, IC 2127) seems to be the most prominent nebula there, looking round and small.

A little higher magnification (63x) shows very subtle nebulosity encompassing the northern half of the "T" asterism. To the northeast, very faint and challenging is the view of the small component N44E (see Figure 4). With averted vision a ghostly nebulosity is visible. For moments, 2 or 3 stars can be discerned there. We will analize that region again using higher power.

At 63x, N44C is the most contrasted nebulosity visible in the whole complex. Stasinska et al. (1986) favour radiative radiation of N44C by a central star whereas Pakull & Motch (1989) suggest that it could be a fossil, X-ray photo ionized nebula formed by a now

Figure 3. LH49 & N44D

quiescent X-ray binary system. "The bright main body of N44C has the appearance of a normal H II region, apart from its high excitation and He II emission. The east, northeast, and northwest boundaries of N44C are relatively sharp and have low [O III]/Ha, indicating the presence of an ionization front" (paper "The He II Emitting Nebula N44C in The Large Magellanic Cloud: Optical/Ultraviolet Spectroscopy of the Nebula and its Ionizing Star" Donald R. Garnett et al. 2000). The area southwest of N44C is visible with averted vision as a rather smooth hazy spot. N44B is round in shape but slightly fainter and smaller than N44C. Even fainter is another round nebulosity, DEM L 140, to the northwest of N44B. It is smaller than the other two mentioned nebulosities. The OB association LH47 contains 40 blue stars according to Lucke & Hodge (1970) and appears, through an 8-inch telescope, as several stars embedded in a faint hazy background. Roughly north of LH47 we find another section of the complex visible like an elongated faint nebulosity (N44I) where a chain of few stars, situated in the same direction of the elongation, can be visible (surely members of the association LH48).

Using UHC filter...

Figure 4. The N44 complex

The view of the small nebula southwest of the star HD 35978 improves clearly using this nebular filter, being visible even with direct vision. It looks smooth without stars present there. Fainter nebulosity is visible toward the west, part of the N44D section of the complex. The shape seems to be a kind of triangle.

Through this filter N44C is, by far, the most contrasted nebulosity. On the other hand, N44B looks a little smaller and less contrasted but easy to see however. Beyond the view of the bright patches N44C and N44B, the nebulosity connected to N44C from the southwest is the most obvious section of the bigger area when using averted vision. The whole big section is visible even with direct vision however. The nebula southwest of N44C is slightly more prominent that the small and round patch DEM L 140. A dark lane crosses the zone between N44C and N44B. It seems to be situated closer to N44B. The view of N44I and LH48 improves using this filter.

Using averted vision a small hazy spot, the zone of BSDL 1363, is visible among the subtle nebulosity right west of N44B.

N44E is, without a doubt, the faintest area of the whole complex visible through a UHC filter at this magnification. It is hard to see, visible for moments using averted vision.

Figure 5. LH48 & N44I

118x, without filter, is a good magnification to observe N44. The zone of IC 2128 and N44D is visible involving three stars situated there. At this magnification the region N44K comes to the view being visible as a round, faint, and smooth hazy spot. Averted vision is necessary to see it. The stellar association BSDL 1449 is visible with averted vision as a short and narrow hazy strip. N44C and N44B look round in shape with the first one a little more contrasted and bigger. The dark area crossing between both objects is again visible. DEM L 140 is, as aforementioned, fainter, so averted vision must be used to see it better. A star or point-like core is visible within it. A region that looks similar to DEM L 140 at this power is the one immediately northwest of N44B, maybe slightly wider and showing also a central star. LH47 is a conspicuous association in the field of view. In the bigger section, the whole stellar and nebulae structure there seems to connect to the region LH48-N44I which appears as a faint nebulosity with a few stars associated.

Figure 6

Using a UHC filter N44D is visible with direct vision. N44K can be barely glimpsed also, while averted vision makes possible to see the whole southern region better. Moving to the northern region, the patches N44C, N44B, and DEM L 140 stand out. N44C looks smooth in brightness along with its extension to the southwest that also looks smooth and fainter than N44C. The nebulosity in LH48-N44I is a little more conspicuous through this filter.

At 160x the section N44H is visible using averted vision, looking rather irregular. N44K is, undoubtely, a challenging object for an 8-inch telescope. At this magnification a hint of nebulosity seems to be present among the faint stars there. The view of N44C, N44B, and DEM L 140 along with the association LH47 is interesting. N44C and N44B appear very similar in size, with N44C slightly brighter. Different than N44C that looks smooth, N44B shows a few stars embedded there. A short observation of N44C a few days later using a 24-inch telescope at 192x showed the nebulosity labeled with the arrow in Figure 6 as a smooth "cometary tail" or fan-shaped hazy structure emerging from the bright and round structure of N44C. Another dark lane, less prominent than that between N44C and N44B, is visible between N44B and the more elusive DEM L 140. The structure surrounding LH47 and connecting to the bright spots in the northern region (i.e. Shell 1) was not visible at any magnification. Using a 24-inch (61cm) telescope the loop Shell 1 was not visible neither.

Which section is NGC 1929?

As with IC 2128, I found some discrepances about the object in the complex which is named NGC 1929. This situation is outlined in Figure 7. While sources like STSCI DSS web page

Figure 7

give the object indicated on the left panel, other good sources like SIMBAD Database indicate that NGC 1929 is the object on the right panel. An historical identification by Dreyer is the following, NGC 1929 (= GC 1135 = JH 2840, 1860 RA 05 22 02, NPD 158 03.6) is "faint, preceding of group", the latter comment presumably meaning it is the western member of a group of objects. According to the Revised NGC/IC project web site, NGC 1929 is a diffuse nebula or a supernova remnant. The ESO`s web page talks about a cluster of stars when NGC 1929 is mentioned. Have in mind these differences if you search for this object using these sources. In this article I adopted the designation DEM L 140.

The LMC, a surprising nearby galaxy to explore with your telescope from the Southern Hemisphere in spring and summer.

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1_ LHa-120 N is the full name of an entry in the Henize catalogue of LMC emission nebulae. "L" refers to the Lamont-Hussey Observatory of the University of Michigan; "Ha" means the Hydrogen-alpha emission line, the key signature line used in the survey; "120" refers to the plate number (objective prism plate) for the LMC; "N" labels the object as a nebula, as distinct from a star (label "S").

2_ DEM is a catalogue of 357 nebulae in the Large Magellanic Cloud and 167 nebulae in the Small Magellanic Cloud that was published in 1976 by R.D. Davies, K.H. Elliot, and J. Meaburn. The LMC catalogue is DEM L and the SMC catalogue is DEM S.

3_ The concept of a stellar association was originally introduced in 1949 by V. A. Ambartsumian, who later separated them into OB and T associations (Ambartsumian 1968). Morgan, Sharpless, & Osterbrock (1952) considered as a stellar association any loose group of stars within an area where bright OB stars exist and with evidence of a common origin.

A recent definition of a stellar association (Kontizas et. al. 1999) refers to it as a single, unbound concentration of early-type luminous stars, embedded in a very young star forming region.

4_ LH is a catalogue of OB associations in the Large Magellanic Cloud compiled by Lucke & Hodge.

Planetary Nebulae - Part 2

Some Fascinating Planetaries Inhabit 

the Constellations of the Winter Southern Skies 

Part II. Ring planetary nebulae

A winter starry night anywhere in the Southern Hemisphere shows a region in the sky, between Right Ascension 12 and 19hs, where some constellations like Crux, Centaurus, Norma, Ara, and Sagittarius host some interesting planetary nebulae. The four objects included in part I of this article are bipolar planetaries, one of the five types in the morphological classification by Schwars et al. (1992), i.e. Elliptical (e), Bipolar (b), Point symmetrical (p). Irregular (i), Stellar (st). Part II of "Intriguing Planetary Nebulae" is devoted to the so-called ring or annular planetaries. Below there are three good examples of this kind of planetary nebula. As an observer, you surely know the Vorontsov-Velyaminov classification which classifies ring-shaped objects as type 4.

If you have at least an 8-inch telescope, all of the planetaries mentioned in this article are visible. Of course, you will be able to find more features or analyze their morphologies in more detail if you observe them through bigger instruments. 

Shapley 1

The observing site in Pampa El Leoncito. The dome of the 2.15m telescope 
of CASLEO observatory is visible in the middle of the photo.
CASLEO  is situated about 14kms from this site in a straight line.

In the inconspicuous constellation Norma, in the southern sky, a fine and faint planetary nebula resides. I am talking about Shapley 1 which shows a nice annular shape at least in astrophotographies. Shapley 1 (α = 15h 51m41s , δ = −51◦ 31′ 23′′, J2000), discovered by H. Shapley (1936), was described as “nearly perfectly circular” in appearance by Bond & Livio (1990), see the paper "The morphology and kinematics of the Fine Ring Nebula, planetary nebula Sp 1, and the shaping influence of its binary central star⋆" by D. Jones et al. (2011). A hypothesis states that Shapley 1 is actually an axisymmetric nebula viewed almost pole-on. It is also classified as type 4 in the Vorontsov-Velyaminov classification scheme. Sources give a visual magnitude of 12.6 for this planetary that is also named PK 329+2.1.

I observed this planetary in two nights from a very dark site just a few kilometers north of CASLEO observatory in San Juan province, Argentina, in the majestic Andes mountain range. The first night was good enough to carry out deep-sky observation but the seeing was not as good as the second night. Even a cold wind bothered most of the night. 

At low galactic latitude, immerse in the band of the Milky Way, we can find this fine annular shape planetary nebula, a target for an 8-inch telescope if you know where to aim it in the sky.

Picture taken using the Photopic Sky Survey ©Nick Singer.

After aiming the telescope to the zone where Shapley 1 lies (see map above) I could found the 1-degree field of view surrounding the planetary. Shapley 1 is situated between the stars labeled with circles in Figure 1. The three stars linked with a red line helped for an accurate search of the position of the planetary as it forms a "rhombus" with them. 

Figure 1. 1-degree field of view with Shapley 1 at the center. North is up.

At 63x without a nebular filter, the planetary is not visible (at least that night under the aforementioned conditions). However, a UHC filter helps to detect the ghostly image of Shapley 1. It can be barely glimpsed using averted vision appearing like a very faint nebulosity rather smooth in brightness. The target was low in the sky for a more detailed observation that night (around 25°), so I decided to make another observation the following night. 

A new observation earlier in the second night (at the end of the local astronomical twilight) made possible to see the planetary higher in the southwest sky (37°). This higher altitude plus a more steady sky made possible a better detection and view of this Milky Way object. At 63x, Shapley 1 could be glimpsed even without a nebular filter, looking like a very faint, roundish, and hazy smooth patch. Applying a UHC filter the view definitively improves. Through this kind of filter, the object is undoubtedly visible. Averted vision makes possible to detect, for brief moments, the west edge appearing slightly brighter than the rest of the planetary (indicated with A in Figure 2).

At higher magnification (119x) Shapley 1 can be barely seen using averted vision. Now some faint stars can be identified in the zone, like those indicated with arrows on Figure 2 that is very elusive through an 8-inch telescope and you need averted vision to barely glimpse them. One of them is the central star of the planetary which has a visual magnitude of 14 according to several sources. That central star seems to be a close-binary central star system according to D. Jones's paper. At this magnification, it is visible with averted vision appearing very faint. Moreover, other faint stars are detected in the area. At this magnification, the detection of the planetary is faint through a UHC filter. However, this power makes it possible to detect the inner central part of Shapley 1 darker, a suggestion of its annular morphology. Again, the west rim of the planetary seems to appear slightly brighter when saw it with averted vision.

Figure 2. DSS image of Shapley 1 showing its annular shape.

North is up. East to the left.

At 162x the planetary appears very faint at the eyepiece. The faint stars aforementioned look a little easier, but they are still elusive. Because of their positions, that stars help to delineate the shape and angular size of Shapley 1. UHC filter helps but the view at this higher magnification is ghostly and challenging.                                                                  

Shapley 3

Position of the peculiar planetary nebula Shapley 3 in the winter southern sky.

Picture taken using the Photopic Sky Survey ©Nick Singer.

Figure 1. DSS image of Shapley 3. The gray circles on the image indicate areas of

brighter stars

Late August is a good moment to observe another remarkable planetary nebula, Shapley 3, which was first reported by Harlow Shapley in 1936. According to the book "Hartung`s Astronomical Objects for Southern Telescopes 2nd. Edition" by David Malin and David J. Frew, this planetary nebula is visible in an 8-inch telescope as a faint circular glow 30" wide. This object, also known as Hen2-341 and PK342-14.1, has a magnitude of 11.9 and a diameter of 36". To find this planetary is easy because it lies only 56 arc minutes to the south of the naked eye star Theta (θ) Arae (visual magnitude 3.7). If you can find NGC 6397 and enjoy the view of this nearby globular cluster, it can be useful to know that the planetary lies about 4.8 degrees northeast of it. 

Using the Optimum Magnification Methods and considering that a visual magnitude of 11.9 and an angular size of 0.6 arcmin are accurate values, the optimum magnification to detect this Milky way´s nebula is 100x for an 8-inch telescope working under a 6.2 limiting magnitude sky. So, let`s see what I could see at different magnifications from a site that offers not exceptionally dark skies but dark enough to carry out this kind of observation.

Figure 2. DSS image of Shapley 3 and its surrounding stars

At low magnification (42x) the field where Shapley 3 lies is rich in stars. Several of them are bright (around magnitude 9) for a telescope. In Figure 1 I indicate with circles the zones where the brighter stars lie. The zone between those mentioned areas shows not too many stars and all of them are faint. At this power, the stars linked with a blue line were used as a starting point to find the accurate position of Shapley 3. Without a doubt, this planetary is a challenging target for an 8-inch telescope. In spite of that, it can be barely glimpsed using averted vision as a quasi-stellar object, very small in apparent size. The very faint stars immediately surrounding this object can be also detected using averted vision, like the one indicated with the arrow in Figure 2 that was useful to find the accurate position of the planetary nebula. Using the Orion Ultrablock filter the planetary looks like a very small hazy spot. Averted vision is necessary to glimpse this faint object. With UHC the view is slightly improved. However, at this low magnification, the view is difficult appearing as a subtle and small hazy dot.

At 78x the faint neighboring stars are better viewed so it is easier to identify Shapley 3 in the field. Now the planetary nebula looks, even with direct vision, like a faint and small nebulosity surrounding a central star, which jumps to the view more easily when applying averted vision. With a UHC filter, the view is very different. It improves the view of the planetary a lot, appearing still faint but with a clear nebular nature, round, and rather smooth in brightness. For moments the central region appears brighter because of the presence of the central star. The view through the Orion Ultrablock filter is not so useful as that with the UHC filter. Shapley 3 does not appear so detached as with UHC. The central star is better viewed, always surrounded by subtle nebulosity.

Shapley 3. Image from Simbad database

Higher power, like 106x, allows you to see the central star which is better detected using averted vision. This 12 magnitude star is surrounded by a very subtle nebulosity. UHC filter improves the view of this planetary nebula appearing as a round hazy spot of smooth brightness that can be identified from the surrounding stars. Dark adaptation is a must for an optimum view of this faint object. Using the Orion Ultrablock filter at this magnification the view did not depart from that without a filter. It was not as useful as the UHC in order to get a better contrast.

I got similar results after observing Shapley 3 with a little higher power (148x). However, the planetary appears even fainter, especially through the UHC filter. Orion Ultrablock offers a not so detached view of this object when comparing with UHC.

IC 4642

IC 4642 is a faint planetary nebula situated in constellation Ara, not so far from NGC 6397, one of the nearest globular clusters.
Picture taken using the Photopic Sky Survey ©Nick Singer.

IC 4642 ©R. Corradi et al.

For those observers who want to look for more challenging planetary nebulae with an 8-inch telescope, this one is an interesting target situated at the core of constellation Ara. IC 4642 (also PK 334-9.1) was discovered by Williamina Fleming in 1901. Some planetarium software, like Skymap for example, classifies this object as type 4 (ring shape in the Vorontsov-Velyaminov scheme). This planetary nebula is listed in the paper "Precessing Jets and Point-Symmetric Nebulae" by J.A. Cliffe et. al (1995) as having a bipolar/point symmetric symmetry. 

This 15" size object is immersed in a field that shows several faint stars. Some brighter stars are visible in the east half of the field of a telescope working at low magnification. In a 1-degree field, the brightest star is the 8.3 magnitude HD 154970. The stars linked with a blue line in Figure 1 are useful to find the planetary which forms a sort of "question mark" shape along with four faint stars of 11 and 12 magnitude (linked with pale blue lines on Figure 2 below). The 12 visual magnitude variable star V788 Arae, a semi-regular pulsating star according to the Simbad Database, is indicated in Figure 2 with a blue arrow. To use that asterism makes the identification of IC 4642 very easy. At low magnification (63x) and without any nebular filter IC 4642 is visible, appearing like a very small hazy disc that can be glimpsed even with a direct vision.

Figure 1

Averted vision, on the other hand, allows seeing a more detached view. A UHC filter improves the contrast at this power.

Jumping to a higher magnification (118x) the view of IC 4642 is more obvious at the eyepiece, clearly looking like a small, round nebulosity among the surrounding stars. Through a UHC filter, the view is definitively beautiful with the planetary detached against the background sky, rather smooth in brightness, and circular in shape. An Orion Ultrablock filter also improves the view, which is pretty similar to that obtained with the UHC filter but somewhat brighter through an 8-inch telescope.

This power (160x) makes the planetary to appear round and smooth in brightness. With averted vision the core of this object appears to look a little darker for moments, suggesting (in a rough way of course) a ring-type structure. Seeing conditions at the moment of this analysis was not the best, so it would be good to make another observation under more optimum conditions to compare results. The observation using the Orion Ultrablock shows a round and smooth nebula. Averted vision makes possible to detect what appears to be a point-like feature, slightly brighter, on its west side (indicated with a white arrow in Figure 2). It is important to say that this feature was very difficult to confirm.

Figure 2

At 222x IC 4642, round in shape, seems to show a somewhat darker core. However, this view is very subtle. Nebular filters, as in other cases, helped to show a more detached view of this planetary.