Some notes from a few weeks ago - one of my first sessions with my new Ethos 17mm
Observations 14/3/2013
Telescope 400mm f4.9 tri-dob reflector
Eyepieces 28mm UWAN, 17mm Ethos,13,9 mm Naglers, Paracorr
Navigation: Uranometria, Night Sky Observer’s Guide
Seeing excellent, transparency fair
p=preceeding f=following
NGC 2257 GC in Dorado
175x 4’ round smooth soft glow with indistinct edges, no resolved stars, no core and a triangle of foreground stars on the following edge (one of the LMC’s GCs)
NGC 2249 OC in Dorado
175x 2’ round and concentrated soft glow with no stars resolved and no core (catalogued as a GC in Uranometria but listed as an open cluster in the LMC by Archinal and Hynes)
H60b11 GC in Dorado
175x Near NGC 2249, it could be its twin, but perhaps a little larger and brighter.
NGC 2210 GC in Dorado
175x 2’ bright round concentrated luminosity with distinct core and perhaps a slightly grainy appearance. One of the 13 GCs of the LMC
NGC 2442 GX in Volans
175x 7’ wide p-f bar with bright nucleus. A 4’ arm sweeps from p end and heads Sf. 3’ arm from f end heads Np and is slightly fainter
10’ f is the 2’x1’ p-f glow of ES9-11 (GX) and 20’ N is the 2’ distinct round glow of GX NGC 2434
NGC 2808 GC in Carina
135x One of my favourite GCs, stunning in the 17mm Ethos, myriad stars resolved, a bright and concentrated GC with a dense core sitting in a magnificent starfield.
Then some fantastic views of Eta Carinae nebula, NGC 3532, Omega Centauri with 17mm Ethos and then Ghost of Jupiter at 660x!
175x 7’ wide p-f bar with bright nucleus. A 4’ arm sweeps from p end and heads Sf. 3’ arm from f end heads Np and is slightly fainter
10’ f is the 2’x1’ p-f glow of ES9-11 (GX) and 20’ N is the 2’ distinct round glow of GX NGC 2434
Hi Paddy,
You were doing well to see the fainter of the two spiral arms as clearly as you did see it, because it is structured very differently from the brighter of the two arms;
the fainter spiral arm can look more like a short stub, at times, and it is "smeared and broadened" in its appearance;
I recall a paper by Mihos & Bothun which explains the unusual arm structure and the unusual bar-like structure in this galaxy, by reference to a model in which NGC 2442 encounters a smaller galaxy.
(the longer and brighter of the two spiral arms is well-behaved, pointy, and quite narrow)
You say in your observing notes that one of the spiral arms is slightly fainter than the other one. This is arguably true, though I myself reported a substantially greater difference between the brightness of the two arms, in my own visual observations. In general, my own observing notes (from several visual observing sessions) tend to support a much bigger difference between the length of the two spiral arms than you report in your own observations.
There is indeed a "bar-like" main body in this galaxy, but if you compare this bar structure to what is found in virtually every other barred spiral galaxy, the bar structure is not at all what you typically find in the majority of other barred-spiral galaxies.
The apparent (two-dimensional)(as viewed on the image plane) morphology of N2442 is in fact very interesting and noticeably unusual, in terms of the unusual bar structure and the unusual arm structure.......so it comes as no surprise that I have been puzzling about this galaxy for many years!
I am interested in your observations of the "nucleus" or "centralmost compact brightening" in this galaxy; because these high-surface-brightness regions at the very centres of galaxies can actually be easier to see in visual observations than in photographs. Q. Paddy, how star-like is the "apparent nucleus" that is seen in your observations, or how diffuse is it? Is it really stellar in appearance, or does it have a certain extent?
I note that it is more accurate not to refer to the visually-observed central brightening in a barred-spiral galaxy as being an actual "nucleus", because this term is reserved in professional astronomy for the tiny & virtually stellar "point-like source" of light that is often seen at the very centre of many galaxies.
What you are seeing as a "nucleus" in NGC 2442 could/might be some mixture of several different superposedthree-dimensional structures:
- a central star-like source of light (e.g. this could be, for instance, a Nuclear Star Cluster plus a Seyfert Nucleus)
- a star-forming region (which is often called a Starburst Region) that surrounds the stellar-like nucleus. This star-forming region may have a disky or flat shape (when it is seen in three-dimensional space).
- a small but significantly-extended Bulge or Spheroidal structure (with mainly old stars, and shaped like a prolate or oblate spheroid)
[[ These three central Morphologically & Kinematically distinct Stellar Population components are commonly found at the centers of barred spiral galaxies; though not every individual barred-spiral galaxy contains all three of these components.]]
Best Regards,
Robert
Oh, and one more strange thing about this galaxy.....
in NGC 2442, the plane (or planes) in which the spiral arms exist, arguably has a different orientation in 3-D space to the plane in which some of the more inner structures exist. This galaxy is one of the many "exceptions" in the bright galaxy population, where a galaxy is not occupying a single plane in 3-dimensional space!
P.S.
Some of the above information is derived from my own analysis of the two-dimensional morphology of NGC 2442 as imaged at various wavelengths. I have yet to read this recent paper analyzing the structure of this galaxy: http://iopscience.iop.org/0004-637X/723/1/530
Last edited by madbadgalaxyman; 05-04-2013 at 12:06 AM.
Nice report Paddy,
I've just got my new scope & you guys have sparked my interest.
Thanks phil
Hi Phil,
I don't know what is your exact level of observing experience, but I do know that most Deep Sky observers are obsessed with seeing the faintest parts of spiral galaxies ; the spiral arms!!
I can understand this, because all Visual Observers want and need to push their eyes to the absolute extreme-limit of detection, when viewing Very Low Surface Brightness (= intensity divided by sky area) nebulae and galaxies.
[[ In fact there is an amazing resource on techniques that can be used by observers in order to see as faintly and as accurately as possible ; the thread called "How to Hone Observing Sensitivity and Accuracy" ]]
However, strangely, I have become something of a contrarian, and I have campaigned to popularize the great and enduring interest of the brightest and most easily detectable part of a galaxy.......the central part, nearest to the centre of a galaxy.
Some of the most intriguing, mysterious, and important phenomena are viewable in the bright central parts of galaxies:
(1) Active Galactic Nuclei ( a good example is the "stellar-appearance" nuclei of NGC 1566 and M77)
A more distant example is the powerful Seyfert Nucleus that is seen within the distant edge-on spiral IC 4329A
(2) Rings of supergiant HIIregion/OB-star complexes surrounding the "stellar-like" true nucleus of a galaxy. A very good example is the easily observable star-forming ring which is seen at the centre of NGC 1097
(3) Nuclear Star Clusters, which are actually similar to a very-overluminous globular star cluster that contains several different ages of stars. One of these that might be visually observable is the Nuclear Star Cluster at the centre of NGC 300. (A related type of object is the "young globular star cluster" found in NGC 1705)
(4) Small bright bulges (spheroidal structures) seen at the centres of many galaxies that have long and strong bar structures
(5) Mini-bars : Mini-bars are tiny and Very Bright bar structures that are completely distinct from the large-scale bar found within a barred-spiral galaxy. Some galaxies have a small bar which is nested within a larger bar!! (I seem to recall that NGC 1291 has an exceedingly faint & low-contrast "large-scale bar", but it also has a Very-high-contrast & Bright central Mini-bar structure)
cheers,
Mad galaxy man
Other galaxies with prominent Nuclear Star Clusters include NGC 7793 (see recent imaging thread about sjastro's NIR image of this galaxy) and NGC 4244
Last edited by madbadgalaxyman; 06-04-2013 at 11:10 AM.
I don't know what is your exact level of observing experience, but I do know that most Deep Sky observers are obsessed with seeing the faintest parts of spiral galaxies ; the spiral arms!!
I can understand this, because all Visual Observers want and need to push their eyes to the absolute extreme-limit of detection, when viewing Very Low Surface Brightness (= intensity divided by sky area) nebulae and galaxies.
[[ In fact there is an amazing resource on techniques that can be used by observers in order to see as faintly and as accurately as possible ; the thread called "How to Hone Observing Sensitivity and Accuracy" ]]
However, strangely, I have become something of a contrarian, and I have campaigned to popularize the great and enduring interest of the brightest and most easily detectable part of a galaxy.......the central part, nearest to the centre of a galaxy.
Some of the most intriguing, mysterious, and important phenomena are viewable in the bright central parts of galaxies:
(1) Active Galactic Nuclei ( a good example is the "stellar-appearance" nuclei of NGC 1566 and M77)
A more distant example is the powerful Seyfert Nucleus that is seen within the distant edge-on spiral IC 4329A
(2) Rings of supergiant HIIregion/OB-star complexes surrounding the "stellar-like" true nucleus of a galaxy. A very good example is the easily observable star-forming ring which is seen at the centre of NGC 1097
(3) Nuclear Star Clusters, which are actually similar to a very-overluminous globular star cluster that contains several different ages of stars. One of these that might be visually observable is the Nuclear Star Cluster at the centre of NGC 300. (A related type of object is the "young globular star cluster" found in NGC 1705)
(4) Small bright bulges (spheroidal structures) seen at the centres of many galaxies that have long and strong bar structures
(5) Mini-bars : Mini-bars are tiny and Very Bright bar structures that are completely distinct from the large-scale bar found within a barred-spiral galaxy. Some galaxies have a small bar which is nested within a larger bar!! (I seem to recall that NGC 1291 has an exceedingly faint & low-contrast "large-scale bar", but it also has a Very-high-contrast & Bright central Mini-bar structure)
cheers,
Mad galaxy man
Other galaxies with prominent Nuclear Star Clusters include NGC 7793 (see recent imaging thread about sjastro's NIR image of this galaxy) and NGC 4244
Thanks for that Mgm(for short)
I've had a good scope for about 3-4 years & have recently upgraded it so i can see more of the fainter objects that i enjoy looking for, i like planetary neb & galaxies & galaxy clusters, interacting galaxies.
I have a few friends that are very experienced, so i have learned a bit & seem to be able to observe faint object not to bad.
i do enjoy reading your & a few others reports it gives me something to look at & compare how i see it.
i will read how to improve you observing ,always looking to improve skills,.I do agree i like nothing more than seeing detail in a faint object.
I will check out those targets you have suggested & a few more
I do agree i like nothing more than seeing detail in a faint object.
I will check out those targets you have suggested & a few more
Are you in a dark site?
thanks phil
Phil,
I am, these days, only an occasional visual observer. Though between 1971 & 1999 I was a regular at dark sky sites, and I soon decided that I was only interested in viewing galaxies!
Most of my work/play now involves comparing and contrasting tens of thousands of galaxy images, with a view towards understanding the morphologies and properties of the the bright galaxies in the nearby universe (the sample that I study is several thousand individual galaxies, to a limit of Blue magnitude 13.5-13.7)
I have also collected very large amounts of data, from many Galaxy Catalogs and many Galaxy Atlases and also from scientific papers, about many of these galaxies;
perhaps I will publish this information (online, and/or in paper form) one day.
These days, I use "other peoples' data" because I find that visual Deep Sky observing can show only a limited amount of detail on galaxies, due to the low resolution of the eye at faint light levels that thereby causes galaxies to look fuzzy when viewed in the eyepiece.
(However, my fundamental knowledge of galaxies has been greatly aided by having viewed many galaxies with my eye)
I recommended a very unusual form of visual galaxy observing in my previous post....... because the central regions of galaxies are relatively bright, and an angular resolution of 1-2 arcseconds, which is sometimes available to the deep sky observer, can show interesting detail.
I may try to write a post for the "observational and visual astronomy" forum, explaining in more detail the sorts of structures that can be seen in the central parts of spiral galaxies.
Interesting obs Paddy. Looks like you got some excellent seeing. You sure do well with resolving structure in galaxies, the one time I observed 2442 I don't recall seeing much besides a featureless smudge. How did the Ghost of Jupiter appear to you at that magnification?
Here is a sketch I did with an 8" at 600x in near perfect conditions
Interesting obs Paddy. Looks like you got some excellent seeing. You sure do well with resolving structure in galaxies, the one time I observed 2442
Mr PGC Hunter!
Yeah, Paddy has got excellent visual sensitivity, as is plainly seen from his observations of galaxies.
I used to have excellent sensitivity when in my 20s and early 30s, but now that I am a much older bugger, I don't detect vanishingly-faint light as well as I used to.
My observation notes from "way back when" indicate that I had a very tough time seeing much detail (with a 10 inch) in NGC 2442 under normal dark-sky conditions, but I eventually did succeed in clearly seeing the bar and also the two (very different from each other) spiral arms; however, the sky conditions had to be very very good in order for me to accomplish this, which is an indicator that the surface brightness of this galaxy must be particularly low;
the NED extragalactic database gives both major & minor axis of this galaxy as being about 5 arcminutes, as does the ESO-LV catalog, so this object is very very extended!
cheers,
Robert
See also: in the astro-imaging forum, I have included an infrared image of this galaxy, in the thread about NGC 7793 by sjastro.
Last edited by madbadgalaxyman; 07-04-2013 at 06:02 PM.
Wow! Thanks Robert for another one or two of your very illuminating responses. Amazing. Very interesting to read what you say about observing the brighter parts of the galaxies. I will re-read your post a few times before the next observing session and see if I can train my eyes more fully.
With regard to NGC 2442 I have observed it quite a few times and I have excellent skies to the south, so usually get a pretty good look at it. From memory, the central brightening looked extended rather than stellar. Thanks for the correction about the term nucleus. Very good point.
I really appreciate the time you put into these posts and like to go over them a few times as it takes quite a bit to get my head around them.
Sab, the Ghost of Jupiter at 660x was AMAZING!!! couldn't put it intos words. I owe you a debt because your reports were what encouraged me to ramp up the magnification on PNs. Fantastic!
Wow! Thanks Robert for another one or two of your very illuminating responses. Amazing. Very interesting to read what you say about observing the brighter parts of the galaxies.
With regard to NGC 2442 I have observed it quite a few times (....) From memory, the central brightening looked extended rather than stellar.
(.....) Thanks for the correction about the term nucleus. Very good point.
Thanks, Paddy,
It is not that hard, really, to figure out the structures of galaxies, even for an amateur astronomer, as the literature on the morphology and classification of galaxies is :
(1) Quite small.
(2) Relatively Non-technical and non-mathematical,
.......therefore the Classification of objects is always something that amateurs can do.(as per the 'galaxyzoo' amateur-professional collaboration)
While it is helpful for Visual Deep Sky Observers to know the exact definition of 'nucleus' and also to understand the several other structures that can be found in the central parts of galaxies, this knowledge may still not be helpful, in practical use;
because what we need to find is a way for deep sky observers to more accurately describe , in their observing notes, what they see in the central parts of various galaxies.
As is, visual DS Observers tend to use the word 'nucleus' in a very imprecise way, using this word to describe a central brightening which could be stellar or which could be significantly extended.
It would be helpful if I could prepare a guide to what can be seen in the centres of galaxies, illustrated with photographs. I hope I can "get a round Tuit".
Best Regards
Robert
P.S. I have always been impressed by Steve Gottlieb's observing notes about galaxies; he does a very good job of describing what he sees.
Have you seen my recent threads in the science forum about massive compact young star clusters? (e.g. NGC 3603 and Trumpler 14). These objects are possible for visual observers to see, but they are very challenging objects for the visual observer...... on account of their compactness and their significant distances away from us.
Last edited by madbadgalaxyman; 25-04-2013 at 08:30 AM.
"P.S. I have always been impressed by Steve Gottlieb's observing notes about galaxies; he does a very good job of describing what he sees."
Thanks for the compliment, Robert. I'll throw in my observing notes on NGC 2442 with a larger scope (24"), which mentions appearance of the central region ---
24" (4/4/08): I was amazed how prominent the sweeping spiral arms appeared at 260x giving a stunning "S" appearance. The main bar of the galaxy is fairly bright and extended ~2:1 in a SW to NE orientation with a length of ~3'. The bar has just a weak, broad concentration with no real core but it rises sharply at the center to a very small, brighter nucleus. The main arm is attached at the NE end of the bar and extends a short distance in that direction before dramatically bending sharply to the west (turning nearly 150°) and extending ~3.5' in length towards a mag 12.9 star. At the NW end this well-defined arm fades and broadens a little, terminating just SE of the 13th magnitude star. At the SW end of the bar, a thick arm emerges extending to the SW where it more gently curves around towards the east while fanning out. This arm is not as sharply defined as the inside (east) portion of the curve blends with a diffuse glow extending from the bar. The total distance between the tips of the arms spans nearly 5'. In the same field 10' ENE lies ESO 59-11 and NGC 2534 is 16' NNW. The field also includes a number of mag 9 to 11 stars that frame the galaxy.
Thank you for your characteristically detailed and interesting observations of N2442
It is hard to say, really, what three-dimensional morphological component the apparent bar actually is;
it could be a filled-in ring structure of some sort, or it could actually be a disk which is inclined to the line-of-sight. I have pondered this issue several times, but I can't seem to come to any conclusions!!
I suspect that the nucleus of which you speak in your observations probably corresponds to what would in previous days have been called a small bulge (= a spheroidal component composed mainly of old stars)
However, the bulge in this galaxy appears to be a pseudo-bulge, in that it looks like it has a disky (flattened) morphology; many barred-spirals do not have much of a real spheroidal bulge, instead having an inner mini-disk (which was formerly called a bulge)
Now I admit that this is cheating, but here is an HST closeup of the apparent bulge. Sure looks more like a disk!
The morphological components within spiral galaxies are clearly and comprehensively described in this paper:
(Kormendy & Kennicutt, 2004, ARAA, 42, 603)
This is very useful stuff, as it helps observers and theorists of all types, to come to a clear understanding of the known structures found within disk galaxies.
Further to previous post, I thought that perhaps a good near-infrared image of this galaxy might make the overall structure clearer.
I just Found this one on the internet, taken with Gemini South telescope and the FLAMINGOS-2 instrument in December 2011 in good seeing.
It is a composite of J and H and K exposures (1.2 microns ; 1.6 microns ; 2.2 microns)
The central small mini-disk is extremely obvious in the low-extinction near infrared regime.
But why don't the two principal spiral arms link to anything as they curve inwards??!? One possibility is that they might plausibly link to a weak ring structure surrounding the central small disk.
(It is quite common for spiral arms in galaxies to start from a ring structure, rather than from the very centre of a galaxy)
Another very odd thing about this image is that if you turn up the brightness and contrast, there is a very strongly rectangular structure in the central parts of this galaxy.
Its all quite puzzling really, as nothing is quite "as it should be" in this galaxy.
