Stellar Clusters in Messier 31

OBSERVING REPORT

G1 - GLOBULAR CLUSTER (DWARF GALAXY CORE?) IN ANDROMEDA GALAXY

Date: September 19, 2014
Time: -
Telescope: 20" (50cm) f/3.55
Observer: Leo Cavagnaro

Click on the image to enlarge

Finder Chart

How to find it,
About 2°40' to the southwest of the core of Messier 31

Stars in map up to visual magnitude 8
Deep-sky objects up to magnitude 13

The 100-inch telescope at Mt. Wilson.
Photo taken by Leo Cavagnaro.

Andromeda`s was the first extragalactic globular cluster system to be discovered (Hubble 1932). Hubble was able to distinguish Andromeda`s clusters on plates taken with the 100-inch reflector at Mount Wilson Observatory, California, USA. Since Hubble`s identification of 140 cluster candidates many authors have added to the list of cluster candidates.

The first detailed spectroscopic and photometric study of the cluster system was done by van den Bergh (1969) with the Palomar 200-inch Hale Telescope (see paper "Extragalactic Globular Clusters. II. The M31 Globular Cluster System" by John P. Huchra et. al. 1990).

This DSS image gives a clue about how you should see G1in a half a
degree field of view.

Also known as Mayall II, it was first identified as a globular cluster candidate by Mayall & Eggen (1953) using a Palomar 48-inch Schmidt plate taken in 1948. It was subsequently named G1 by Sargent et. al. (1977) in their survey with the Kitt Peak 4-m Mayall telescope of GCs in 29 fields surrounding M31 (see paper "Structural Parameters of Mayall II = G1 in M31" by J. Ma et. al. 2007).  G1 is the brightest globular cluster in the Local Group of galaxies. At a distance of 2.9 million light years it shines at 13.5 visual magnitude.

You must aim the telescope to a zone about 2.5 degrees to the southwest of Messier 31`s core to find it. Through a 20" telescope at 300x the cluster can be identified among two very close stars which form, with G1, a very small and tight equilateral triangle (look at the pictures). The globular cluster definitively looks non stellar at this power. Averted vision improves the view of it.

In the paper "Mayall II ≡ G1 in M31: Giant Globular Cluster or Core of a Dwarf Elliptical Galaxy?" (G. Meylan et. al. 2001), the researchers state that this globular cluster, like ω Centauri, has been considered as the possible remaining core of a former dwarf elliptical galaxy which would have lost most of its envelope through tidal interaction with its host galaxy.

_________________________

OBSERVING REPORT

C107 - OPEN CLUSTER IN ANDROMEDA GALAXY

Date: September 19, 2014
Time: -
Telescope: 20" (50cm) f/3.55

Observer: Leo Cavagnaro

How to find it,
About 29' to the southwest of Messier 32.

Position of C107 in Andromeda Galaxy (Messier 31).

With a magnitude of 15.1 and a size of 5.7 arc seconds this stellar cluster, situated not very far from the star cloud NGC 206 (about 7 arc minutes due south of this object), is clearly visible through a telescope of this size at 300x. Averted vision helps to get a better view. At this magnification it looks like a very small hazy spot immersed in the nebulous background produced by the Andromeda galaxy.

Striking Nebulae in the Large Magellanic Cloud

Published in the April 2013 issue of the Rosette Gazette newsletter (Rose City Astronomers, Portland Oregon USA)

Bright Emission Nebulae and a Supernova Remnant

are Found in the Northeast Region of our Satellite Galaxy

The sky is getting darker at Uspallata Valley1, in central-west Argentina. Slowly, the Magellanic Clouds become visible in the Southern Sky. Hidden not too far from the heart of the Large Magellanic Cloud (LMC) an interesting complex of small nebulae resides. The question arises, how much you can see there with a common 8-inch telescope? Is this area of that galaxy impressive enough to observe and study with this kind of optical instrument?

I have tried to describe in this article all the details you can observe in this complex, in fact, one of the most interesting within our satellite galaxy.

The Southern Sky in summer. The Large Magellanic Cloud (right on the picture) is an astounding unaided eye object, together with the Eta Carinae Nebula (upper) and the Coalsack Nebula (middle left). Photo by the author.

I spent two nights, March 8 and 9 (2013), to observe a small region centered at R.A. 05h 39m  Dec. -67° 40', which corresponds to the “area 24” of my big observing project about this galaxy. Using an 8-inch telescope and an eyepiece that gave me 37x and a wide field I got a first view of the zone. At that moment, the galaxy was 48° above the horizon. The stars in the field mostly have visual magnitudes fainter than 11. The star HD 38616, with a visual magnitude of 7 (Figure 1), is the brightest one there. On the west edge of the eyepiece field, a nebulae complex is easily visible even without filters. It is, by far, the most conspicuous feature in the field.

The N59 Nebula

Figure 1. The region under observation is situated to the north of 30 Doradus 

(Tarantula Nebula). North is up.

Named LHa-1202 N59, and also known with the name of “Dragon’s Head Nebula”, this HII region is centered at R.A. 05h 35m 25s  Dec. -67° 35' 00´´, at the boundary with the structure known as LMC-43.

Focusing on this complex, three patches are visible at 37x. The brightest and biggest zone, known as N59A (see Figure 2), exhibits the shape of a fan with several filaments which may be ionization fronts, thus making it the third brightest nebula of the LMC after 30 Doradus and N11. It is composed of two regions or maybe just one big region elongated roughly west-east with a dark lane across dividing it into two parts of similar brightness. These two parts have NGC numbers, 2035 and 2032. The first one was discovered by James Dunlop in 1826. The other one, NGC 2032, was observed by John F. W. Herschel in 1834 but surely Dunlop observed it too because it is very similar to the other area discovered by him. “The dust lane seems to be mixed in with the nebular gas and the stars, suggesting a site where star formation may still take place. However, from the morphology revealed by those direct images, it is impossible to ascertain whether those nebulae are physically related or even, whether they are located at the same distance” (extract from the paper “Kinematics of the very young nebula N59 at the edge of the supershell LMC-4” M. Rosado et. al. 1998). N59A is closely related to the OB association4 LH 825, which covers an area of 3´x 6´ and virtually coincides with the nebula.

Figure 2. N59 complex. North is up

A third patch, round in shape through an 8-inch scope, that looks fainter than the other two, lies about 5 arc minutes to the East of the brightest part of the complex, in the region known as N59B (see Figure 2) which is, according to C. Armand, L. Deharveng and J. Caplan in their paper “The Stellar Content of the Large Magellanic Cloud HII Region N59A” (Astronomy & Astrophysics, 1992), a filamentary nebula that includes a photoionized region in the north, a supernova remnant in the south, and a Wolf-Rayet star. The photoionized patch I saw is known as NGC 2040, a diffuse nebula discovered by James Dunlop in 1826 using a 9-inch telescope.

At 48x, the view is more detailed. In the brightest area divided by the dark lane, the eastern patch (NGC 2035) looks slightly smaller while the western patch (NGC 2032) appears bigger, showing two stars at its western edge. An extension of fainter nebulosity, which becomes narrower toward the West when seen through an 8-inch telescope, is visible at this power. I am speaking of NGC 2029 (see Figure 2). On the other hand, NGC 2040 was clearly seen, fainter than the other patches and with smooth brightness. With averted vision, a very small spot seems to lie very close. Maybe the two stars in the region of the supernova remnant? Read more below in this article.

Applying higher magnification (64x) I got a beautiful view of this complex. NGC 2032 and 2035 look very bright. Although both nebulae together are slightly elongated west-east, NGC 2032 specifically is a bit elongated north-south. Even if the overall shape of NGC 2040 is round, at this magnification some clues of irregular shape appear. The small and faint region known as N59C (see Figure 2) could not be visible at this magnification.

In the second observing night I applied UHC filter to this eyepiece to observe this complex. I started the observation at 10:35pm local time (UT-3hours) with the Large Magellanic Cloud at 47° of altitude in the sky. The view was very clear, with the patches NGC 2032 and 2035 obvious in the eyepiece. NGC 2029 is visible as a smooth nebulosity while NGC 2040 is more easily visible than the view with the other eyepieces. Through this filter, it looks slightly fainter than NGC 2032/35. With averted vision, a bright dot is visible within the nebula, maybe a star member of the OB association LH88 associated with NGC 2040. This filter improves the overall view of the complex, being especially useful for a better view of NGC 2029 that shows a triangular shape, getting narrower outwards of the brightest part of the complex. Although it was difficult, the view of N59C, a small, round, and faint nebulosity in the southeast part of the pair NGC 2032/2035 was possible at this power using this kind of filter.

Through an Orion UltraBlock filter N59 looks very well. Like the UHC filter, this one improves a little the view of the whole complex. However, it can be observed without a filter as well. This filter helped for the observation of the two faint nebulae NGC 2029 and 2040.

I spent most of the second night (March 9) observing these nebulae with higher magnification. At 120x, the view of N59 is more interesting and detailed. Each region or patch is clearly visible and identified. NGC 2040, which shows a similar brightness to NGC 2029, and fainter than the two main patches, shows some faint stars embedded in the nebulosity. It is surely the aforementioned OB association LH88 (Lucke & Hodge 1970).

Aiming the telescope to NGC 2032 & 2035, both nebulae look outstanding at this power. NGC 2035 looks round while NGC 2032 appears a bit elongated. C. Armand et. al. point out that the main star that excites the region N59A is an O5 spectral type they name “star 226” in their paper. I indicate it in Figure 2 with a small red circle. The detached black lane between the bright nebulae adds an interesting view to the region. NGC 2029 looks faint at this magnification, being better viewed using averted vision.

Figure 3. The [S II]  emission (yellow) defines the supernova

remnant. Picture from Smith et. al. 1999. North is up.

With a UHC filter, NGC 2029 and NGC 2040 show similar brightness. A slightly brighter region is visible within NGC 2029 (look Figure 2). For a brief moment, a star is visible within NGC 2040. On the other hand, N59C is still difficult to see even with this filter, being necessary averted vision.


An Extragalactic Supernova Remnant

A supernova remnant, known as SNR 0536-676, is situated in this complex. It was identified as such by Mathewson et. al. (1985). It appears to be a blow-out of the dense HII region N 59B around the OB star association LH 88 (Chu & Kennicutt, 1988).

I invited my friend Carlos Gutierrez to observe this elusive object using a 16-inch telescope. A first observation at 106x made possible to identify two very faint stars situated in a key position to try to delineate the shape and size of the supernova remnant. They are indicated with the red arrow in Figure 3. After that, we tried to see some nebulosity in the region immediately to the South and West of NGC 2040. However, it was impossible to view at this magnification and under the observing conditions that night. Using a UHC filter with this eyepiece, an extremely faint, elusive, and small nebulosity could be glimpsed in the region indicated by the ellipse in the picture, which is coincidental with the brightest portion of the supernova remnant. The view was very difficult and it was close to a “retinal torture”.
This elusive nebulosity is also visible in the DSS image in Figure 2. There it looks a little brighter than N59C but it was harder to see even through this bigger telescope. The nebulosity labeled with the square in Figure 3 was also visible using averted vision for both of us. Carlos stated that it has a triangular shape, narrowing toward NGC 2040. According to the picture, this nebulosity seems to be not a part of the supernova remnant, but an extension of the NGC 2035 region.

Figure 4. N70 nebula. North is up

At 144x, the two stars are clearly visible and another star (to the North) is also detected. The small patch close to the stars is visible for some moments. The zone enclosed by the square shows a faint star within (visible in Figure 3). With a UHC filter, the view is similar to that at 106x.

The N70 Nebula

Also known as DEM L6 301, it is one of the most outlying bright emission-line objects, located in an isolated region of the disk, far from supergiant shells (Meaburn 1980), H II regions, and bright diffuse H-alpha emission, a textbook example of an isolated superbubble. “It is an especially prominent bubble of line-emitting gas which appears to be powered by a population of hot massive stars in its interior” (paper, "Emission-Line Properties of the LMC Bubble N70", B. Skelton et. al. 1999). To observe this object you need a very dark sky, good dark adaptation, and patience to detect the faint nebulosity situated 45 arc minutes to the southeast of N59.

Figure 5. The cluster NGC 2053 (left). North is up.

At 37x, the view of this nebula was interesting. It looks faint on DSS (Digitized Sky Survey) images and it is extremely faint when you try to see it visually under a dark sky. It can be hardly glimpsed even without a nebular filter through an 8-inch telescope. A good way to find it is to identify the triangle of stars (lower edge in Figure 4), and then to move about 15 arc minutes to the North. Once there, you will be able to identify a close pair of stars with visual magnitudes 10.8 and 12.5 (white arrow in Figure 4). Very close to it, a faint nebulosity can be glimpsed using averted vision. Two stars within the nebulosity are also visible, one of them looks like a defocused faint star and is coincidental with the position of the OB association LH 114. This is an association consisting of at least nine stars of type B0 or earlier (Oey 1996a).

At 48x, I could clearly identify the double star. Observing in the area of this nebulosity, a very small and compact stellar group is detected where LH 114 lies. This compact group appears surrounded by a faint and smooth nebulosity, N70.

At 64x, in the central zone within the faint nebulosity, a sort of “defocused star” can be glimpsed. For a moment, and using averted vision, 2 or 3 stars very close to each other seem to lie in the zone. At this magnification and using a UHC filter, N70 looks a little more detached from the surrounding sky, but it is a very faint object. Averted vision suggests its round shape, showing a smooth and faint brightness. At the center of the nebulosity, the small region slightly brighter is easily distinguishable.

Through an Orion UltraBlock filter, the view is very similar. The stellar nature or content of the small central region embedded in nebulosity can be confirmed.

How does N70 look using 120x? Well, the stellar configuration mentioned above is easily identified in the eyepiece field and the faint nebula can be glimpsed, showing smooth brightness and engulfing the stars there. LH 114 appears like a small and compact stellar group, and some members can be spotted using averted vision. The view with a UHC filter is not very different.

In the outskirts of the complex N59, to the northeast, two small hazy spots are visible. Averted vision helps to see them better. According to the DSS image one of them, indicated with a red arrow in Figure 5, is a group of 3 stars surrounded by faint nebulosity. At low power (37x) and using averted vision it looks nebular and a little elongated, suggesting the 3 stars in a raw. Higher magnification is necessary to see it in detail. I personally don´t know if these stars are members of the OB association LH 92. I could not find detailed information about this association, but the DSS image obtained from http://archive.stsci.edu/cgi-bin/dss_form shows the area of the three stars as the place of LH 92. The other one is the open cluster NGC 2053 (see Figure 5) discovered in 1837 by John Frederick William Herschel, an object with a magnitude of 12.2 according to the NGC/IC Project web page and the Wolfgang Steinicke's Revised NGC and IC Catalog. The zone of the two objects seems to be connected with faint nebulosity. The three stars are in the region known as DEM L 250. The DSS image of this nebula shows the three stars at the center.

At 48x, the three stars are better viewed very close to each other. NGC 2053 looks, with averted vision, as a small hazy spot of smooth brightness. I got the same view of this open cluster at a little higher magnification (64x), appearing round in shape. At 120x, this cluster looks faint but appears relatively big in the field of this eyepiece. Averted vision improves the view. At this power, the three stars were clearly visible and no nebulosity was glimpsed there.

At 64x, I saw a “star” that looked faint and surrounded by a kind of very small nebulosity, appearing as a defocused star. You can see it does not show the point-like appearance of the stars if you compare it with the nearby (only 2.5 arc minutes away) 9.3 magnitude star HDE 269804. Observing this area with 120x, I could see a very small group of 2 or 3 stars very close to each other. Later, when I checked the DSS image, I identified the three faint stars on the picture (see the small panel on the right hand of Figure 5).

Once again, I am amazed how small details and faint objects can be observed with an 8-inch telescope when they are carefully observed using good charts, deep-sky images (DSS for example), and having a peaceful and dark place to observe from.

_________________________________________________________________________

1_ It is situated about 75 miles to the west of Mendoza city, in Los Andes mountains. It is a good place to observe the skies. Geographic coordinates, 32° 36´ 32” S 69° 21´ 18” W.

2_ LHa-120 N- This is the full name of an entry in the Henize catalog 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").

3_ LMC4 is a kpc-sized ring of H II regions in the Large Magellanic Cloud.


4_ 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.

5_ LH is a catalog of OB associations in the Large Magellanic Cloud compiled by Lucke & Hodge.

6_ DEM is a catalog 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 catalog is DEM L and the SMC catalog is DEM S.

Open Clusters in Cassiopeia

OBSERVING REPORT

OPEN CLUSTERS IN CASSIOPEIA

Date: September 15, 2012
Time: -
Binocular: 9x60
Observer: Leo Cavagnaro

I started an observing project late that night so in the meantime I decided to observe some open clusters that lie in the beautiful constellation Cassiopeia, waiting for the moment of the beginning of my major observation.

Messier 52. Trumpler classification I,2,r. This 5 kly distant cluster, situated roughly 43 arc minutes south of the 5 magnitude star 4 Cassiopeiae, is visible through this kind of binocular. A few stars seem to be discerned when you see it from a dark sky site. It was discovered in 1774 by Charles Messier.   

NGC 7789. Trumpler classification II,1,r. Through this kind of small optical device, this open cluster looks like a round nebulous patch, appearing rather faint. However, it is an object for binoculars.
It was a discovery of Karoline Lucretia Herschel in 1783. It can be found aproximately 51 arc minutes south-southeast of the 4.5 magnitude star ρ Cassiopeiae.

NGC 129. Trumpler classification IV,2,p. Small stellar swarm close to the 6 magnitude star HD 2626, a double star according to the SIMBAD Database. Some of the brightest members can be glimpsed using averted vision. Friedrich Wilhelm Herschel discovered this object in 1788. NGC 129 lies at the middle of the imaginary line that connects the bright stars β (Caph) and γ Cassiopeiae.

NGC 225. Trumpler classification III,1,p,n. It looks like a faint hazy patch in the central part of constellation Cassiopeia, between the stars κ and γ Cassiopeiae. Known as the Sailboat Cluster, it is a loose and poor cluster. It was discovered in 1784 by Karoline Lucretia Herschel (sister of William) using a 4-inch reflector telescope.

NGC 457. Trumpler classification I,3,r. This cluster, discovered by Friedrich Wilhelm Herschel in 1787, usually known as the "ET" or Owl Cluster, is easy to find because you just need to aim your instrument to the naked eye star φ Cassiopeiae (visual magnitude 5). The cluster, that looks like an elongated nebulosity through a binocular, is detected immediately to the northwest of that star. In some sense, this cluster reminds me a short tail of a comet. Some stars can be glimpsed when using averted vision.

Stock 2. Trumpler classification III,1,m. Situated about 5° south-southeast of the 3.4 magnitude star ε Cassiopeiae (Segin), it is an interesting open cluster, big, and elongated in the same orientation that the double cluster of Perseus (W-E). It is a swarm of stars with similar brightness that is easily discerned through a binocular. Stock 2 lies within a triangle formed by three stars (visual magnitudes between 6.5 and 7) that are brighter than the cluster members.

NGC 7635, The Bubble Nebula

OBSERVING REPORT

NGC 7635 - THE BUBBLE NEBULA in Cassiopeia

Date: August 15, 2012
Time: 07:51 UT   LOCAL TIME (UT-7hs.)
Telescope: 24" (61cm.) f/4
Observer: Leo Cavagnaro

Click on the image to enlarge

Finder chart 

How to find it,
About 1° 10' to the south-southwest of the star 4 Cassiopeiae (visual magnitude 5).
 

Stars in chart up to visual magnitude 6.0

NGC 7635 (Bubble Nebula).

This nebula is formed by gas being compressed by a strong stellar wind from “Wolf-Rayet” massive star BD+602522. NGC 7635, discovered by Friedrich Wilhelm Herschel in 1787, lies not too far from the well-known cluster, for the northern stargazers, Messier 52 (about 35 arc minutes to the southwest), in the constellation Cassiopeia. A pattern of five stars (linked with gray lines in the DSS image to the right), with visual magnitudes between 8.7 (the brighter one) and 10 (the fainter one), helps to identify the nebula in the field of view of the telescope. The nebula surrounds one of the stars of the pattern, the 8.7 visual magnitude BD +602522 that lies to the side within the nebulosity. I have indicated the star with the white arrow in the lower DSS image.

At 59x through a 24-inch telescope and an OIII filter, the nebula looks smooth in brightness. The outer parts look fainter than the central region near the star. At higher magnification (122x) and using a nebular filter (OIII), the structure of NGC 6735 is very interesting, showing bright nebulosity surrounding the star with a small region even brighter immediately to the west of the star BD +602522. Fainter nebulosity is visible, elongated northwest-southeast.

Close-up view of NGC 7635 and its brighter region. 

North is up.

The Crescent Nebula

OBSERVING REPORT

NGC 6888 - THE CRESCENT NEBULA in Cygnus

Date: August 15, 2012
Time: -
Telescope: 24" (61cm.) f/4
Observer: Leo Cavagnaro

Click on the image to enlarge

Finder Chart

How to find it,

About 2°45' to the southwest of the 2.2 visual magnitude star Sadr (γ Cygni).

Stars in map up to visual magnitude 6.

NGC 6888 is an easy object to see through a 24" telescope working at low magnification (60x) and an OIII filter. NGC 6888 is associated with WR 136 (HD 192163), considered to be a member of the Cygnus OB1 association. The observations of 62 galactic WR stars in the northern sky show that about half are associated with nebular emission (Miller and Chu 1993), some of which are ring nebulae. Johnson and Hogg (1965) were the first to propose that these ring nebulae were formed by stellar wind interaction with the local interstellar medium.

At the mentioned magnification, this nebula looks clearly elongated with an oval shape and the rim showing higher brightness. The small area indicated by the arrow in the DSS image (left) is the brightest part of this object. The northeast rim looks brighter and narrower than the opposite one, which looks wider and fainter. The inner part of this object is less prominent in nebulosity, appearing fainter.

A Complex in the Vicinity of 30 Doradus

Published in the May 2012 issue of the Rosette Gazette newsletter (Rose City Astronomers, Portland Oregon USA)

A Notable Chain of Extragalactic Nebulae is Displayed to Visual Observers to the South of the Famous “Tarantula Nebula”

The nebulae complex near 30 Doradus (indicated with a circle in the picture).
North is up. Image from Photopic Sky Survey. 

©Nick Risinger

Summer in the Southern Hemisphere is the best season of the year to observe the Magellanic Clouds. If you are South of declination +15° take a look at the 30 Doradus region, a starburst region in the Large Magellanic Cloud usually known with the colorful name “Tarantula Nebula”. It is impressive even in small telescopes, showing dark and bright features of nebulosity.

But if you want to know a little more about the HII regions content of our satellite galaxy, just aim your telescope about 35 arc minutes due south of that bright nebula, in fact, the brightest and biggest of this kind of object in our nearby galaxy, and you will find a very interesting field displaying several nebulae and some small clusters. I am referring to a 1° field centered at R.A. 05hs 41m  Dec. -69° 41' J2000.0 (see Figure 1).

A first view using 42x made possible to see a set of objects and nebulae structures grouped in the northwest quadrant of the eyepiece field. Different than the case of 30 Doradus for example, whose shape is well known, these nebulae are visually obvious but their not well-known appearances made the identification of them a bit hard, at least in my case. Some asterisms were easily recognized using a reference chart, thus making possible to verify that the field under observation was correct.

The Chain N158, N160, N159

DSS image of the three major regions in the complex.

North is up.

About half a degree south of 30 Doradus lies a line-shaped group of three nebulae named N158, N160, and N159. Using low magnification (42x), all of them were visible even without any nebular filter, detaching from the background sky and surrounding field and being, by far, the most interesting and brightest objects there.

Under a dark sky, a UHC filter works properly, displaying, at low magnification, an astounding field where the nebulae structures appear very detached. With the whole complex centered, extended and elongated zones of nebulosity are visible in the northwest part of the eyepiece field. Prominent nebulosity exists in the area connecting 30 Doradus with the N159/160 complex. Through this filter, NGC 2080 in the N160 region is the brightest zone of the whole complex (UHC works very well in this case). On the other hand, N159 looks more detached with a similar brightness of that of N158 (LH 101 region).

The Cloud N158

Figure 1. 1-degree eyepiece field  centered at R.A. 05h 41m
Dec. -69° 41'. The field shows the complex south of 30 Doradus.
North is up.

The structure closest to 30 Doradus is named N158 (see DSS picture below). In the paper “The OB associations LH 101 and LH 104 in the HII region N158 of the LMC”, G. Testor and V. Niemela state that the northern part of this region is composed of a superbubble around the OB association1 LH 104, while the southern part, containing the OB association LH 101 and dominated by unevolved and evolved O-type massive stars, is a diffuse HII region which is characterized by three bright zones. Using the mentioned magnification, the area coincident with the OB association LH 101 is the brightest part of the whole complex understudy, rivaling in brightness with the zone in NGC 2080, situated farther south, where the small blobs named A1 and A2 are situated (read more about this below). In the zone of the OB association LH 101 at least five stars are visible (visual magnitudes around 10 and 11) forming a sort of crown-shaped asterism that is better viewed using averted vision. Very close to this asterism, on the side opposite to the position of 30 Doradus, a small and bright nebulosity is clearly visible, N158C (also NGC 2074), an emission nebula + cluster according to  the NGC/IC Project web page, where LH 101 lies. As said, one of the most prominent zones where faint stars could be hardly glimpsed using averted vision. This technique was useful to see the overall shape of the cloud N158, appearing elongated southwest-northeast. The region in the middle of N 158 looked less conspicuous, with a 10th magnitude star (GSC-9167-0702) well detached there, equidistant from both stellar associations and with some faint nebulosity present there. At the other end of the cloud, in the area coincident with the OB association LH 104, the brightness of the complex arises again becoming more obvious (little less bright than the LH 101 zone and a little bigger) showing a similar appearance, with nebulosity and stars situated on the side. The distribution of the nebulosity surrounding LH 104, evident in the DSS image, was not visible at this magnification.

Using the stars indicated with letter D in the eyepiece field as reference (see Figure 1) I tried to identify and see a very small nebulosity near LH 101, labelled with letter A in the DSS image below, but it was not visible under the observing conditions. The asterism marked with red lines was also identified.

Focusing again on N158, the view through a UHC filter was interesting. The middle zone shows more nebulosity if we compare it with the view without it. This filter allowed me to identify the overall shape of N158 better. Like the view without a filter, the zone coincident with LH 101 is the most conspicuous, a bright patch of light with some stars close to it. Helped by averted vision, the elongated central region is visible reaching the zone of LH 104 where stars with some of nebulosity are visible. This area of the complex was observed around 10:30pm local time (UT – 3hs) when the altitude of the target on the sky was around 52°.

A view of N158 using higher magnification (78x) shows the region of LH 101 bright, with a few stars embedded in the brightest zone. A lane of nebulosity seems to follow the shape formed by the distribution of the brightest stars there, suggesting a crown or arc shape. Scanning the rest of this region with this magnification, the middle area looks (like with the lower power observation) less conspicuous. However, some of faint nebulosity could be seen there. At the end, brighter nebulosity is visible embedding the OB association LH 104 where the use of averted vision makes possible the identification of a faint stellar swarm.

At 78x with a UHC filter, the view of this cloud was very interesting because its detailed shape started to be revealed (see DSS image to the right). The OB association LH 101 looks elongated approximately northwest-southeast, the middle zone shows the nebula lane. Observing carefully with averted vision the faint nebulosity surrounding the association LH 104 could be fairly glimpsed.

The region in LH 101 looked like a C-shaped nebulosity at higher power (106x), harbouring a few stars brighter than the others in the nearby surrounding field at both ends of the “C”. The association LH 104 looked like a roundish group of faint stars of similar brightness and nebulosity. HD 38489, an extreme supergiant star, is located in this association and its ultraviolet spectrum is similar to the spectrum of the peculiar Eta Carinae star.

The small and elusive nebula, indicated by A in the DSS image above, could be glimpsed at this magnification using averted vision.

At this magnification and a UHC filter, N158 looked prominent in two sections, one of them coincident with LH101 suggesting again the mentioned “C” shape, with two stars named Sk -69 249 and Sk -69 247 in its northern side, well detached from the hazy background (see lower panel in DSS image above). The other section is situated between the central star of the cloud reaching the zone of LH104, appearing like a pretty faint and smooth lane of nebulosity. 

N158 is the third richest area of the Large Magellanic Cloud for WR stars2.

The Complex N159/N160

According to a team of researchers from Universidad de la Plata and Casleo Observatory in Argentina, Carnegie Institute, and the Space Telescope Institute, the field south of 30 Doradus is particularly rich in clusters, associations, and nebulae, including the N159/N160 complex. This field also contains the most massive CO concentrations in the LMC, so it may be expected that in a few million years 30 Doradus successor will appear there (you can read the paper “Spectroscopic Study of the N159/N160 Complex in the Large Magellanic Cloud”, Cecilia Fariña et. al. 2009).

The HII Region N160 and the “Ghost Head Nebula”

Moving the telescope away from N158, in the opposite direction to 30 Doradus, we find another region of the complex under observation, N160. Yasushi Nakajima et. al. in their paper “Near-infrared Imaging Observations of the N159/N160 Complex in the Large Magellanic Cloud: Large Clusters of Herbig Ae/Be Stars and Sequential Cluster Formation”, The Astronomical Journal (2005), divide N160 in two parts, N160-north and N160-south. The first one (older) is situated in the zone coincident with an asterism I could easily identify and I indicate with a red line in Figure 1. On the southern side of the asterism, and indicated with an ellipse, faint and smooth nebulosity can be seen at 42x even without a filter, reaching the N160-south region which shows some prominent features. 

At 78x, very faint nebulosity was visible with faint stars present there. The nebulosity was also visible through an UHC filter but the view was not improved. 

At 106x and UHC filter the nebulosity was very hard to see, so lower magnification was better in this case.

What Happen in N160?

N160 region containing NGC 2080, the "Ghost Head Nebula". A1 and A2 blobs 
are the bright dots at the ends of the chainnear the center of the picture. 
Photo obtained by the author using a 16-inch remote-controlled telescope 
installed at La Punta Observatory in San Luis Province (Argentina).

The more interesting and conspicuous feature in this part of the complex, appearing at 42x like a small and round nebulosity (in my opinion the brightest feature of the whole complex under study) is N160A. Actually, it is an NGC object (NGC 2080) discovered by John Frederick William Herschel in 1834. It is the nebular patch in the middle of the HII regions under observation, nicknamed the “Ghost Head Nebula”. NGC 2080 requires higher magnification for more detailed observation. To the southwest and very close (bounded) to NGC 2080 a small, faint, and round nebula were visible. The star HDE 269953, the brightest one in the area (visual magnitude 9.9), was visible immersed in faint nebulosity in the zone where the nebulae NGC 2085, 2086, and IC 2145 lie (see Figure 2). At this magnification, these nebulae were not visible at all.

Using a UHC filter, NGC 2080 looks very bright and small suggesting a slight elongation. Again, the faint nebulosity close to this object was detected. To the east-southeast, two “stars” were visible embedded in a zone of nebulosity.

The view of NGC 2080 at 78x and without a filter starts to suggest two small patches of nebulosity with similar brightness. They are very close to each other and to discern them was very hard, so higher magnification was necessary for a better view. Faint nebulosity was viewed very close to those patches and at this power it seems to engulf them. The view of NGC 2080 and the nearby nebulosity through a UHC filter was similar.

About 2.7 arc minutes to the east-southeast of NGC 2080 a group of small objects lies (see Figure 2). A pretty faint and small hazy dot was visible as a little defocused star. According to the position given by the STScI DSS web page it is IC 2145. The zone connecting this object with NGC 2080 displays faint nebulosity that was better viewed using averted vision.

Figure 2. The N160 region. North is up.

The star indicated with the arrow in Figure 2 and IC 2145, a diffuse nebula according to the NGC/IC Project web page, were visible at 78x and a UHC filter. That source indicates the position of NGC 2086, another diffuse nebula, coincident with that star. I found an observing report where it is stated that NGC 2086 is a very small nebula almost hidden by a 10th magnitude star, while the STScI DSS web page gives, for NGC 2086, the same object of that for IC 2145. The sharp and bright view of the star through a UHC filter in my 8-inch supports the idea of the nebulous nature of this object and/or the immediate surrounding area. Whatever the case, both the "star/nebula" object and IC 2145, appeared embedded in fainter nebulosity. Observing carefully, a faint “dot” was visible within that nebulosity close to the mentioned star.

The view of the “Ghost Head Nebula” at 106x was very interesting and worked very well to see the details of this region in the middle of the complex. Averted vision suggests the presence of three bright and small patches (see the picture I took with the remote telescope). These patches are surrounded by faint nebulosity. This nebulosity is also visible toward the southwest where a faint star is visible within it, near the center. Through a UHC filter, it was not easy to discern the three patches of NGC 2080, the zone showed a sort of “granularity” and appeared bright.

The two hazy objects, IC 2145 and NGC 2085, close to the star HDE 269953 (Figure 2), looked very small resembling distant and compact open clusters. The fainter one (NGC 2085) is situated close to the star, the other one (IC 2145) is a little brighter and was easier to see.

A final observation of NGC 2080 using high magnification (360x) in a 16-inch telescope, to try to see “the eyes”, showed a blurry image. However, a sort of chain of small nebulous objects embedded in nebulosity could be seen.

NGC 2080, the Ghost Head Nebula.

Copyright: ESA, NASA, & Mohammad Heydari-Malayeri
(Observatoire de Paris, France)

The “Eyes of the Ghost”

Heydari-Malayeri & Testor (1986) discovered two compact HII regions embedded in N160A, identified as N160A1 and N160A2, the “eyes of the ghost” (bright spots in the picture to the left). These objects belong to the special class of so-called High Excitation Blobs (HEBs3) in the Magellanic Clouds. HEBs are very dense small regions usually 5” to 10” in diameter. A1 (left) is powered by a single massive star. A2 (right) harbors several exciting stars enshrouded by large quantities of dust. The best part of this story is they can be glimpsed through a common amateur telescope like 8 inch using high magnification and good seeing conditions!

The N159 Cloud

Interesting! Roughly round in shape, this cloud has maybe the most striking appearance of the three patches in the complex. The line of three stars (with visual magnitudes between 9.4 and 11) labeled B in Figure 1 was used as a guide to identify this HII region. 

At 42x, N159 looks like a round and smooth nebula with a few bright spots on the periphery (I talk about them below) distributed in the form indicated by arrows in a sketch I made. Through an 8-inch telescope and without a nebular filter, the dark feature across the “disk” in N159 was glimpsed for moments using averted vision and observing carefully (see DSS image – Figure 3).

Sketch of N159 made by the author showing the four patches 
seen through an 8-inch telescope. Two are nebular in appearance
(below in the sketch)and the other two look stellar (up in the
picture).

The brightest patch, and easier to see, is N159A (also NGC 2079), situated on the southwest corner of N159. The “patch” labeled A in Figure 3 looked like a star and it is coincident with the position of LMC X-1 (read about this object in N159´s Features section below). A higher power was necessary to observe and identify the east region, where NGC 2084 and a supernova, named SNR 0540-697, are situated.

Using the same magnification with a UHC filter the view was clearer because N159 looked more contrasted against the background sky and definitively round in shape. The dark lane across N159 was glimpsed with averted vision. Only two of the four spots in N159 were clearly visible through this filter. N159A is, by far, the more obvious, being visible like a defocused star o very small spot of nebulosity. Fainter and less contrasted is the other patch situated inner in N159 (see Figure 3). Its position seems to match that of NGC 2084. However, higher magnification was necessary in order to have a better view.

Figure 3. North is up.

At 78x, NGC 159 was clearly visible. It is still necessary to use averted vision to discern the black feature inside. The four “patches” are again visible; two of them are undoubtedly hazy in appearance, somewhat similar in apparent size. The other two clearly look like stars.

At the same magnification but this time using a UHC filter, the cloud looked round and smooth in brightness. The two hazy patches were detected immediately, especially N159A which is the brightest one. In fact, N159A is brighter than the rest of the N159 cloud. Using the configuration offered by the two stars indicated with A and B in the lower panel in Figure 3, and the nebula N159A, the other patch seems to be NGC 2084. This was confirmed later having an observation of the zone with a 16-inch telescope that made possible the identification of other features situated between both patches, indicated with white arrows on the lower panel in Figure 3. According to the NGC/IC Project web page, NGC 2084 is a bright nebula. Once again, the black feature was barely visible using averted vision.

An observation of this object at 106x (a good magnification) showed the two round hazy patches. They look similar, with N159A slightly smaller and brighter.

As usual, for most of the nebulae, the H-beta filter did not work to observe N159, being the image totally blocked.

N159´s Features

A Supernova Remnant and an X-ray source

A recently identified supernova remnant lies within N159. I am talking about SNR 0540-697, which is situated at RA 05h 40m 00s  Dec. -69° 45' 10” (J2000.0) according to MCELS (The UM/CTIO Magellanic Cloud Emission Line Survey). On the northeast corner of N159 a small zone, slightly brighter than the rest of the cloud, was visible through an 8-inch telescope at 78x and nebular filter in the zone coincident with the position of the supernova remnant. However, 0540-697 is not an object for amateur astronomers. The supernova remnant, discovered by Chu et al. (1997), is difficult to observe in optical and radio due to emission from the surrounding H II region N159.

The 14.8 magnitude star #32 is the optical 
counterpart of LMC X-1, a radio source in 
our satellite galaxy. This photo appears in 
Figure 2 in the paper "Determination of the
Optical Counterpart of LMC X-1" (A.P. Cowley
et. al. 1995).

Not too far from this remnant, indicated in the DSS image with letter A, we find LMC X-1, which is (with Cyg X–1) one of only two known persistently luminous x-ray binaries consisting of a black hole accreting the wind of a massive blue star (“The nature and cause of spectral variability in LMC X–1” L. Ruhlen et. al. 2011). I think the star visible there through my 8-inch telescope at different magnifications is surely R148, a B5 type supergiant star in LMC with a visual magnitude of about 12.5, one of the four “patches” in N159. The fainter star very close to R148 labeled #32 in the photo to the right, is probably the optical counterpart of the x-ray source LMC X-1.

The “Papillon Nebula”, an elusive object

Situated in the HII region N195, this small nebula is also the prototype of the HEB family, “High-Excitation Blobs” (Heydari-Malayeri & Testor 1982) that constitute a rare class of ionized nebulae in the Magellanic Clouds, according to the paper “Stellar Populations Associated with the LMC Papillon Nebula” by F. Meynadier et. al. (2004),. It is known with the name N195-5 and its angular dimension is about just 2x2.8 arc seconds. It is not visible in an 8-inch telescope.

If current researches are right… will generations in a remote future see maybe “a new 30 Doradus” in this part of our neighbor galaxy?

_________________________________________________________________________________

1_ 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.

2_ WR Star: Wolf-Rayet stars are hot massive stars (20+ solar mass) with a high rate of mass loss. Strong, broad emission lines arise from the winds of material being blown off the stars.

3_ HEB: Stands for High Excitation Blobs, compact HII regions which 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.