ESO 510-20 Galaxy System

 

Is This Object Within Reach of Big Amateur Telescopes, 

or is it Just a Candidate for Astrophotography?

We are at the end of the summer here in the Southern Hemisphere. Under the usual cool (rather cold) nights at this time of the year (April) in any observing site that offers dark skies, like in the Andes mountains, you can see constellations Centaurus and Hydra, a good reservoir of galaxies and groups of galaxies. The easternmost part of the long constellation Hydra reaches an altitude of 60 degrees around local midnight in late March-early April. The area is high enough to aim a big telescope, like a 24-inch one, and look for a very peculiar and unusual interacting system nicknamed the Dentist´s Chair because of its shape resembling that chair nobody wants to seat on. Other designations for this object are ESO 510-20, PGC 49560, and AM 1353-272 in the Arp-Madore Catalogue of Southern Galaxies and Associations.

Figure 1. The Hydra-Centaurus Region. North is left, East down

Figure 1 to the right plots the distribution of galaxies brighter than magnitude 12. As you can notice, the easternmost end of the long constellation Hydra, at the border with the constellation Centaurus, contains a good sample of galaxies (center of the image).

Figure 1 in the paper "Large Velocity Gradients in the Tidal Tails of the Interacting Galaxy AM 1353 −272 (“The Dentist’s Chair”)" by Peter M. Weilbacher et al. 2002, included in this article as Figure 2 with their permission, shows the galaxy system in detail. According to A. Monreal-Ibero et al. in their paper "Towards DIB mapping in galaxies beyond 100 Mpc A radial profile of the λ5780.5 diffuse interstellar band in AM 1353-272 B⋆". (2015), the system consists of two components. The main galaxy (A) presents two prominent ∼40 kpc long tidal tails. The companion (B) is a low-luminosity disk-like galaxy of disturbed morphology undergoing a strong starburst and with high extinction. They state that component ‘C’ is located 38 Mpc behind the interacting pair. " The long tidal tails of “A” host a number of blue knots. Given their colors, these knots could be physically linked with "A" (paper "On the Formation and Evolution of Dwarf Galaxies in Tidal Tails" by Peter M. Weilbacher 2002). 

Now, is this object within the reach of big amateur telescopes, or is it just a candidate for astrophotography? 

First Observing Attempt

Figure 2

Remember, the results of this observation are based on one single night with the conditions at that moment mentioned below. My plan is to go to another observing site to make a new observation to compare results.

The sky on the night of the observation was pretty steady with a decent seeing. However, I can tell that the night before, during the observing weekend, was darker. The observing site, according to some sources, has a Bortle 2 scale (average dark sky). In my humble opinion, the site might be close to the border with Bortle 3, because although the sky toward the North and West is truly dark, some light pollution from the big city of Mendoza and the much closer but smaller town of Uspallata interfere at low altitude, near the southern and eastern horizons. I guess we can take a visual magnitude of 7 like the average limiting magnitude of the area since it is right in the limit of Bortle 2 and 3. I consider the area good enough to carry out challenging observing projects. For sure you can find even darker skies if you drive some miles northward, closer to the "Pampa el Leoncito", where the biggest observatory in Argentina is situated (CASLEO). Pampa El Leoncito is still a very dark area from where I was able to glimpse, with two observer partners, the Gegenschein a few years ago, giving us the idea of a very good sky. Back to the observing site and the night of the observation of ESO 510-20, I can mention that at the moment of the observation, a slight wind interfered with the analysis. Earlier that day, the wind caused some dust to remain high in the atmosphere, making the sky brighter than the night before (I didn´t measure the limiting magnitude at the observing site).

Photo by the author showing the position of the galaxy system in the sky

Once I aimed the telescope at the region where the target is situated, indicated in the picture above (roughly 9 degrees from the 2-magnitude star Menkent), it was necessary to recognize the surrounding field in detail. Using low magnification to have a field of view around 1 degree wide, some stars are identified, like HIP 68099, a red giant situated about 437 light-years appearing yellow through the telescope. HIP 68099 is the brightest star in the field with a visual magnitude of 6.8. Also, HD 121469, a 9.2 magnitude star, and TYC 6724-613-1 with a magnitude of 10.5, two of the brightest stars in the field close to the galaxy system, were visible.

Figure 3. DSS STSci image

At 76x, you can find the brightest star in the field, HIP 68099, a 6.8 magnitude red giant branch star, the brightest one in the field (see Figure 3). Beyond the mentioned stars, the group of stars encircled by a red ellipse is very useful in a  field of view of 15 arc minutes. That asterism, to the right of the bright star HiP 68099, composed of stars with visual magnitudes between 13 and 15, was useful not only for identifying the field of view, among other stars but also to determine the precise position of the galaxy system. It looks like an arrow pointing to ESO 510-20. At this magnification, of course, the galaxy system is not visible. ESO 510-20 seems to lie roughly equidistant from the stars labeled with blue circles in Figure 3 that can be identified at this magnification. Observing carefully and applying averted vision, a sort of  "star" seems to appear in the area of the galaxy system.

Using 144x, the view of the stars immediately surrounding the position of ESO 510-20 is more clear. However, nothing is visible where the target is. Once again, averted vision makes it possible to momentarily glimpse, very faintly, a ghostly and small dot there. Higher power is a must to try to catch this obscure object of the southern skies.

Even if higher magnification shows a very detailed field regarding the faint stars surrounding the precise area of the galaxy system, it is not evident and averted vision doesn´t improve the very dim ghostly brightness that was also visible at lower magnifications.

After observing for a long time, the target's position in the sky was about 84 degrees, late in the night, so it had a perfect altitude to observe a challenging object. At even higher magnification (360x) the result is the same, hard to glimpse a very small and faint dot using averted vision.

Figure 4. North is up, East to the left

Now, is that extremely faint dot visible with all the magnifications a star situated there, or can be maybe the brighter core of the largest component of the galaxy system? Making a photo of the galaxy system dimmer (Figure 4), simulating in some way what I could see through an eyepiece, you can notice that component A (the brightest one) and the round feature to the northeast (component C in Figure 2) remain visible, so maybe that is what I could see because seemingly no stars brighter than the system´s core lie there according to the DSS image.

Conclusion

So, is ESO 510-20 a visual object? Well, you can not expect at all to see the entire shape of this galaxy system, unless you take a deep photo. However, is possible to try to glimpse the brighter central part of component A or even more, component C. Now, based on the single observing night I dedicated to this object I should say it is not an object for visual astronomy. This interactive system seems to be reserved for astrophotographers or observers with instruments bigger than 24-inch. However, I think that it is convenient to make a new observation of this object to determine if a challenging object like this one is visible or not. I think it is always convenient and fruitful to observe the same target again, from the same place or even from a site with better observing conditions (i.e. darkness, transparency, seeing, general weather conditions, etc.) and compare results. 

I didn´t find enough information regarding the visual magnitude of ESO 510-20. The magnitude in B-band is displayed in several sources, like SIMBAD Database, as 15.9. Just by way of example to know the importance of a dark sky let's imagine a galaxy with a visual magnitude of 16 and a size of 0.5 x 0,5 arc minutes (the apparent size of the component A of ESO 510-20  is smaller). Under a dark sky with a limiting magnitude of 7, the hypothetic object should be visible through a 24-inch telescope, with 140x as the optimum detection magnification. The situation changes if the sky is slightly "brighter" (limiting magnitude drops to 6.7 for example). Under this last situation, the target should not be visible, at least in theory. Unfortunately, I did not measure the limiting magnitude that night, but as was aforementioned the night before was definitely darker and for sure with an even higher limiting magnitude. The observation of challenging objects like ESO 510-20 implies a sky as dark as possible, so limiting magnitude is an important variable we need to have into account when organizing this kind of observing session.

The fact of not observing this object through a 24-inch telescope doesn´t mean it is not possible to detect it visually. Besides the mentioned conditions (seeing, weather, limiting magnitude, etc.) an appropriate condition of the observer and the equipment is undoubtedly a must as well (i.e. eye performance, a very well-collimated telescope, appropriate dark adaptation, good use of averted vision, etc.). Two observers under the same sky can achieve different results, depending on their own capabilities and personal conditions at the moment of the observation. I think the question of this article is open. For sure the "Dentist´s Chair" system is a good target for long-exposure photography, but it is, for sure, a challenging target for those observers who like to take their eyes and telescopes to the limit of their performances.

Although the nickname of this deep-sky object can sound "intimidating", it is worth the effort to try to glimpse at least some features of this intriguing interacting system during an observing session on any autumn night in the southern hemisphere. If you can, include it in your observing list!

Lindsay-Shapley Ring

A Peculiar Galaxy, an interesting Target for Big Telescopes, Resides in the Far Southern Skies

As a visual observer, galaxy morphology has always been a very exciting topic for me. To observe different kinds of galaxies, from the classic elliptical and spiral ones to those in groups and clusters showing peculiar shapes is something very interesting, especially if you have a chance to use a big telescope that allows you to detect the fainter and finer details of them. Among the peculiar members in the world of the galaxy morphology, we have the so-called annular galaxies or ring galaxies. As James L. Higdon et al. state in their paper "Why Are Ring Galaxies Interesting?" (2010), these objects are formed by the near central passage of a companion through a spiral along the rotation axis. The brief additional gravitational force induces epicyclic motions throughout the disk, which act to form radially propagating orbit-crowded rings of gas and stars. On other of their papers, James L. Higdon et al. argue that ring galaxies are striking examples of the ability of collisions to transform both the morphology and star-forming activity of a spiral galaxy. Numerical studies since the mid-1970s argue persuasively that the optically prominent rings are in fact outwardly propagating zones of strong orbit crowding within the disk of a spiral induced by the near central passage of a companion galaxy ("Wheels of Fire. IV. Star Formation and the Neutral Interestellar Medium in the Ring Galaxy AM¹ 0644-741" 2011).

The 24-inch telescope at the "Altos Limpios" Nature Reserve. 

Photo by the author.

If you are observing in the Southern Hemisphere during the summer season take a look, for a moment, to the Large Magellanic Cloud. It is a must-to-see object because of its size, brightness, and remarkable structure. Well, now aim your eyes about 8 degrees southeast of that galaxy. In that region of the sky, more specifically in constellation Volans, an interesting annular galaxy resides, 300 million light-years away. I´m talking about PGC 19481, also known as Graham A, the Southern Ellipse, AM 0644-7411 (Arp & Madore 1987), or Lindsay-Shapley Ring.

A way to find this peculiar galaxy is to look for the 5.1 magnitude star alpha Mensae, one of the stars that are part of the inconspicuous constellation Mensa. The galaxy lies about 2.1 degrees east-northeast of it. The J2000 coordinates of the nucleus of this galaxy are R.A. 06h43m06.s18   Dec. −74◦14 10".7.

The Lindsay-Shapley ring galaxy (AM 0644-741) appears in Category 6 of the Arp Madore catalog of Southern Peculiar Galaxies and Associations, a category that includes any galaxy with an apparent luminous ring around it, and attempts to exclude objects which appear to be spiral galaxies which have had their arms tightly wound into nearly circular appearance.

Below, there is a short video by Chandra Observatory about this enigmatic object in the Southern Sky,

Figure 1. Field of view of the Lindsay-Shapley Ring galaxy. 

"In AM 0644 741, we see a strong ring of bright blue stars in the Cerro Tololo Inter-American Observatory (CTIO) and Hubble Space Telescope (HST ) images, with associated HII regions. Unlike the Cartwheel, which shows spokes and is presumed to be a second ring-formation event (Struck-Marcell & Higdon 1993), AM 0644-741 is likely to be the first ring formed" (see the paper "Dynamical Parameters for AM 0644 741" Alex Antunes and John Wallin (2007).

As can be read on the paper "Morphology and enhanced star formation in a Cartwheel-like ring galaxy", F. Renaud et al. 2017), the Lindsay-Shapley Ring galaxy also displays an enhanced star formation activity in the furthest quadrant of its ring to the nuclei (Higdon et al. 2011).

The picture at the top of this article shows the 24-inch (0.61 meters) used to observe this galaxy. It was set up in a good field in the ranger station at the nature reserve named "Altos Limpios". You need to drive for almost 2 hours northeast from Mendoza City, in Argentina, to reach it. It is important to say that I saw this galaxy when it was about 32 degrees high in the sky (it reaches 48 degrees at its highest) and seeing was not the best that night, so maybe better results regarding the structures seen in this galaxy can be achieved with better-seeing conditions and with the galaxy at higher altitude.

The galaxy was searched, at the beginning of the observation, using 98x. After several minutes scanning the area the target was found, appearing, at this magnification, as a subtle nebulosity close to a quasi-stellar hazy spot when observing with averted vision, which is, actually, the core of the galaxy. The ring diameter, in arcsec, is 85 x 49. An asterism formed by 4 stars of magnitudes between 12 and 12.9 for those labeled in Figure 1, and magnitude 14.5 for the fourth one in the asterism labeled with a blue circle, was useful to confirm that the area was the correct (see Figure 1). A star indicated with a black arrow in Figure 1, is visible close to the galaxy´s nucleus.

Figure 2. DSS image of the Lindsay-Shapley Ring galaxy and its 

companions.

The Lindsay-Shapley Ring galaxy seems to be a member, according to the SIMBAD Database, of a small group of galaxies. The two nearest galaxies (at least in projection on the sky) were also detected through the 24-inch telescope. I´m talking about the galaxies LEDA² 19455, situated about 1.2 arcmin southeast of the target galaxy, and LEDA 19454, 1.05 arcmin to the north- northeast (see Figure 2). The first one, a distorted elliptical, was visible using averted vision as a small hazy patch. Both Graham (1974) and Few, Madore, and Arp noted an extended and low surface brightness light distribution between the ring galaxy and LEDA 19455. Partly on the basis of this emission, these researchers concluded that LEDA 19455 was the intruder galaxy. The other companion, fainter, was hardly visible using also averted vision.

Applying a little higher magnification (i.e. 122x), the view was similar to that one at lower magnification. However, the nucleus of the galaxy seems to be a little easier to see, like a faint defocused star. The outer part of the galaxy, including of course the ring structure, shows up when averted vision is applied, appearing as a slightly elongated nebulosity. It is not easy to see, and the beautiful structure seen in those detailed and colorful pictures provided by ground-based telescopes and the Hubble Space Telescope is not detected. The view is rather blurry and faint. The nearby galaxies are again visible, looking faint. LEDA 19455 appears similar to the nucleus of Lindsay-Shapley Ring galaxy, both in size and brightness.

203x is a good magnification to observe the group of galaxies. LEDA 19455 looks now brighter and its presence there is undoubtful, showing a round shape. The LEDA 19454 galaxy is fainter, as said before, but it can be detected. The central part of Lindsay-Shapley Ring galaxy looks bigger and its brightness seems to be smooth. When the galaxy is observed with averted vision, an arc-shaped structure of very faint nebulosity is visible just south of the nucleus

Figure 3. Picture credit of James L. Higdon and John F. 

Wallin, appearing as Fig 2 in their paper "Wheels of 

Fire. III. Massive Star Formation in the "Double-Ringed"

ring galaxy AM 0644-741".  

The view of the galaxy is interesting at 244x. The nucleus is easily visible through this instrument. The whole galaxy looks like a rather elongated nebulosity, a ghostly nebulosity among the surrounding stars in the field of view of the telescope. At this power and observing more carefully, some of the structure, very faint, and indicated with an arrow in Figure 2, seems to be detected for moments. AM 0644-741 possesses twin interlocked rings, each with slightly different centers, position angles, and ellipticity. The double-ring structure makes AM 0644-741 unique among ring galaxies, much like the Cartwheel and its network of spokes. A total of 54 H II complexes were identified in the rings using Figure 2a of the paper "Wheels of Fire. III. Massive Star Formation in the "Double-Ringed" Ring Galaxy AM 0644-741" by James L. Higdon & John F. Wallin (1997). I think the slightly brighter portion visible there, barely visible even with averted vision, are some of the HII regions present in the galaxy. The authors of the mentioned paper state that the most luminous H II complexes tend to be found near the intersection of the A-ring and B-ring (see Figure 3 here) which occurs in an area of the galaxy coincident with the one I observed, indicated with the arrow in Figure 2.

In the SIMBAD Database web page, two x-ray sources are indicated as present in that area also (i.e. [WFM2018] AM0644x1, and [WFM2018] AM0644x2.).

A long time ago, something amazing happened in this distant galaxy, and you can be a witness of that when observing it from a dark sky site.

1 _ Catalogue of Southern Peculiar Galaxies and Associations (Arp, Madore): 6,445 peculiar and interacting galaxies found on IIIa-J southern sky survey plates, types, positions, and characteristic sizes, cross-identifications and selected photographs. 

2 _ (Lyon-Meudon Extragalactic Database). Extension of PGC catalog in the Lyon-Meudon Extragalactic Database 1989: Catalogue of principal galaxies, 1ST edition: N=73197.
The first designation was PGC, but PGC and LEDA are now equivalent.

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.

________________________________________________________________________________________________

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 NGC 3256 Group

A Tidally Disturbed Galaxy, a Galaxy with a Double Nuclei, and Other Distant Members are a Group of Enigmatic Galaxies in the Southern Skies to be Explored by Amateur Observers

Figure 1.Pointing toward the zone where the galaxies are situated, in constellation

 Vela

In the eastern part of constellation Vela (the Sail) a group of faint galaxies (at least for an 8-inch telescope) can be found. March is a good month to observe this constellation because it is at a very good altitude as soon as the sky gets dark, so you can observe objects there for several hours during the last nights of the summer in the Southern Hemisphere. To find the area where this galaxies lie is easy because you can use one of the bright stars of Vela, the 2.7 visual magnitude m (mu) velorum,  a class G (G5) yellow-white giant. From there we can move to the stars HD 92139 and HD 91504 (visual magnitudes 3.8 and 5 respectively) to finally find the faint pair of stars of magnitudes 5.7 and 5.9 that are visible from any site that offers dark skies. Once there, the field of interest (centered at R.A. 10h 29m 25s  Dec. -44° 20`32") is roughly 52 arc minutes northwest of the mentioned pair. The galaxies are distributed roughly South-North (see Figure 3 below). Some researchers state that two groups of galaxies lie there, NGC 3256 and 3263, but are difficult to distinguish from each other spatially. However, many researchers consider at least 15 galaxies to be members of a single large group spread over roughly a few degrees that is called the "NGC 3256 group of galaxies". According to a group of researchers led by Jayanne English, "The most spectacular HI feature in the NGC 3256 Group is a galaxy-sized intergalactic HI cloud (English 1994), which we will refer to as “the Vela Cloud.” The structure, as projected on the sky, is not clearly associated with an individual galaxy but appears to be part of the group" (see the paper "The Vela Cloud: A Giant HI Anomaly in the NGC 3256 Group" (2010).

At low magnification (42x) the field does not show any bright and conspicuous galaxy. Focusing on the southern edge of the field of view (see Figure 3) a very faint hazy patch, somewhat elongated, can be glimpsed. Four stars in a row or a chain seems to lie there, among the galaxy. One of them seems to be the core of the galaxy (see Figure 2). Averted vision is necessary for a better detection. That is the  barred galaxy NGC 3261, discovered in 1836 by John Herschel. An historical identification by Dreyer is "faint, small, round, among stars". SN 2008fw, a supernova of type Ia, was discovered in this galaxy in 2008.

Figure 2. NGC 3261
Credit: The Carnegie-Irvine Galaxy Survey (CGS)

Moving about 15 arc minutes due north another galaxy very small in size (1.90 x 0.5 arcmin , PA: 135 ) resides, NGC 3256B, a  type SBbc galaxy with a magnitude of 13.0 (Data from Wolfgang Steinicke's Revised NGC and IC Catalog). It was not visible through this instrument at the different magnifications used during the observing session (from 42x to 266x). 

Moving farther north, another 18 arc minutes, we find a tidally disturbed galaxy, NGC 3263 (m_v: 11.1mag , SB: 11.8mag per square arcmin), included in category 7b "Jets from Spirals" in the Catalogue of Southern Peculiar Galaxies and Associations by Arp & Madore. At this magnification the galaxy is extremely difficult to detect visually. A very faint hazy structure seems to be there when viewing with averted vision. A close companion, NGC 3262, was not visible.

Reaching the northern edge of the field of view we find, at least on nice deep astrophotos, a couple of galaxies (i.e. NGC 3256 and 3256C), see Figure 3. The last one was not detected at this magnification. Although it is a faint galaxy, NGC 3256 (also AM 1025-433) is the "easiest" member of the group in the field appearing round and rather smooth in brightness when using averted vision. A. J. Mulia et al.  in their paper "Star Cluster Formation and Destruction in the Merging Galaxy NGC 3256" (2016) state that NGC 3256 is a merging pair of galaxies ≈ 36 Mpc away and the most luminous LIRG¹ in the local universe.  The main body of NGC 3256 contains a dense population of clusters, many of which are embedded in the galaxy’s dusty interstellar medium. This galaxy shows two long tidal tails in optical photographs (e.g., Sandage & Bedke 1994).

Figure 3. DSS image of the galaxies in the field

These are, without a doubt, faint galaxies to be observed with an 8-inch telescope at low magnification, being only NGC 3261 and 3256 glimpsed in such a condition. Higher power is necessary for a more fruitful analysis of these distant objects.

At 78x, NGC 3261 is visible faint but with direct vision. It is situated among three stars (see Figure 2 above). Using averted vision, NGC 3261 looks rather round in shape. A small structure, slightly brighter, seems to lie in its interior.

NGC 3263 is a faint member detected using averted vision that makes possible to see it rather elongated with its central zone somewhat brighter.

NGC 3256C, a SBcd type galaxy, was not visible at this magnification. Its magnitude is 12.6, SB: 13.2 (mag per square arcmin).

The galaxy NGC 3256 is visible with direct vision at this magnification. Averted vision of course helps for a better detection. It looks round with a brighter core.

An observation at 106x shows NGC 3261 clearly distinguished from the surrounding stars. It is round and wider than NGC 3256. Toward its center the brightness increases and for moments a star-like structure shows up when observing carefully.

Figure 4. NGC 3263
Credit: The Carnegie-Irvine Galaxy Survey (CGS)

NGC 3263 and its companion NGC 3262 (which is not visible at this power) are visible on the picture to the left. NGC 3263 looks elongated for moments when is observed with averted vision and its brighter zone within it is again visible.

NGC 3256C is not visible while the nearby companion, NGC 3256, is easy to see at 106x, round and with a bright core.

A new analysis of the galaxies using even higher magnification was carried out. At 166x NGC 3261, which looks faint and round, shows a small "granulated" structure when using averted vision. Two stars, very faint and elusive, are visible there for moments.

NGC 3263 is still a faint and elusive galaxy, better viewed using averted vision. At 166x its elongated shape was not clearly discerned.

Figure 5. NGC 3256
Credit: The Carnegie-Irvine Galaxy Survey (CGS)

Is NGC 3262 visible through an 8-inch scope? 

You know that a faint galaxy, a challenging object for a given type of telescope, can be hard to see or glimpsed. The degree of difficulty will depend on how dark, steady, and clean is the sky when you are observing. According to an optimum detection method, an observer under a 6.2 limiting magnitude sky should detect this small galaxy, a companion of NGC 3263 (see Figure 4), using around 100x. Even if it was not a clear image at all, a very small hazy patch, round, seems to be barely seen for moments using averted vision. I was very careful identifying the nearby stars surrounding that target to realized if the gosthly image I glimpsed is the small lenticular companion of NGC 3263. It was also barely visible at higher magnification (266x). Observers with 8-inch telescopes are encouraged to observe this galaxy and get their own conclusion about its visibility. Even though NGC 3256B has the same magnitude than NGC 3262, it was not detected through an 8-inch telescope that night. Maybe the reason is that NGC 3256B is a little bigger in angular dimension (1.90 x 0.5 arcmin). NGC 3256C, with its magnitude of 12.6 and surface brightness 13.2 (mag per square arcmin) should be visible in an 8-inch scope, but for some reason it was not visible during the entire observing session. 

NGC 3256 is clearly visible showing its bright core that for a moment looked offset (maybe suggestion of the more expanded structure of the galaxy visible upper left on Figure 5?). NGC 3256 is included in Category 15 "Galaxies with Tails Loops of Material or Debris" in the Arp-Madore Catalogue of Southern Peculiar Galaxies & Associations. This galaxy also has a peculiar feature, a double (northern and southern) nuclei. Presence of an AGN² at the optically obscured nucleus has been suspected for a long time. AGNs are often found among LIRGs.

Figure 6

A final observation of NGC 3261 at 266x makes possible to see the two aforementioned faint stars in the central region of the galaxy which looks round and smooth in brightness.

NGC 3263 looks, with averted vision, elongated. Brighter areas in the galaxy briefly jump to the view.

The central zone of the merging galaxy NGC 3256 looks rather smooth in brightness. Fainter structure of the galaxy is visible surrounding its core.

In the silence of the vast Universe, these galaxies await being observed by amateur astronomers from sites far away from big urban centers.

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1_ LIRG (Luminous Infrarred Galaxies)are galaxies with luminosities above 10¹¹ L_☉. These galaxies emit more energy in the infrared portion of the spectrum, not visible to the naked eye. LIRGs are more abundant than starburst galaxies. Infrared galaxies appear to be single, gas-rich spirals whose infrared luminosity is created largely by the formation of stars within them. However, some galaxies' luminosity comes from an active galactic nucleus or AGN.

2_ AGN (Active Galactic Nuclei) are galaxies where the nucleus (or central core) produces more radiation than the entire rest of the galaxy. Current theory suggests that there is a supermassive black hole (millions of times the mass of the sun) at the center of AGN.