Pushing the 10" to its limits - Hydra/Centaurus Galaxy clusters 18/2

[§AB]

This morning (18/2) provided the last usable opportunity to do some serious deep sky observing before the moon becomes an all night resident. The 1000km/h gale that threatened to kill my plans yet again had magically subsided leaving wonderful still conditions. Went to bed at 11 last night and woke up at 2, so had only 3 hours sleep and as you can imagine that's not ideal, especially when your mission is to hunt galaxy clusters! :o The scope was outside by 2:10am and I went inside to eat and watch some TV while it cooled. Then I sat in the room with the lights off for half an hour to dark adapt. Went outside at 3am. Collimated, took out the rug and lenses, all the usual hoohaa.

I trained the scope on Saturn to judge the seeing. I couldn't focus at even 146x. It is clear that seeing is terrible. Transparency however was good.

Scope: 10" GSO dob
Time: 3am-5.10am
Seeing: 2/10
Transparency: 3/5
Temp: 15ºC
Dew: Nil to very light


Started off with the Sombrero Galaxy. At 56x, the 10" already showed the dust lane. At 146x and 192x, the galaxy exhibited a bright almost stellar core with a central bulge thinning out into long streaks on either side. The dust lane was obvious. The southern half of the galaxy was far less obvious than the bright northern half.

Next stop was the Hydra 1 Cluster. The MSA plots about 25 galaxies in the immediate area. I stayed in the central region, where a 5th and 6.5th Mag stars lie, inhibiting observation of faint galaxies.

ABELL 1060: The Hydra 1 Cluster.
NGC 3311
A moderately faint and fairly large circular haze at 192x. Magnitude is listed at a relatively bright 11 but SFC brightness is only 13.5 making it more difficult than the mag alone would suggest.

NGC 3309
Lies about 2' W of NGC 3311. Easier to see than 3311, due to smaller size and higher SFC brightness. Mag is listed as 11.3 and SFC brightness 12.5. A magnitude 13.5 star was easily picked up sitting on the galaxy's E edge.

NGC 3312
Faint, mag 12.1 / SFC brightness 13.5 elongated haze in the 10", with elongation in a N-S direction. Located midway between a pair of Mag 5 and mag 6.5 stars, which inhibited observation of ths galaxy somewhat.

NGC 3316
A tiny faint blob about 10' E of 3312. Magnitude is a decent 12.1 but a SFC brightness of 13.5 makes this object fairly difficult.

NGC 3308
Magnitude 12.4, SFC brightness 13.1. Moderately faint, more difficult than NGC 3309. Visible as a small circular haze.

NGC 3307
Located about 4' W of 3309/3311. The magnitude is listed at an excessively faint 14.5 with a SFC brightness of 13.0. Tried to make this one out at a variety of mags from 96x to 192x. Spotted a star-like object around where the galaxy should be but unsure whether it was the galaxy/core itself or just a foreground star. Not confirmed. I'll have to try this one again.

That's as far as I went in Abell 1060, I wanted to check out some other offerings around Hydra/Centaurus before dawn so next stop was M83. M83 is easily found by starhopping from 4.5 mag 1 Centauri. On the way came across a nice galaxy, NGC 5253.

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NGC 5253
Lovely, bright elongated (NE/SW) galaxy at 192x, with a nice, tight core. Mag is 10.7 and SFC brightness 13. Smaller telescopes should reveal the bright core.

M83
This zenith muncher is best seen at low power. Observed it at 96x. Bright almost stellar core surrounded by a circular disk of much fainter haze.

NGC 5078
This one surprised me. Photos show a brillant large edge on spiral with a nice dark lane bisecting it. The 10" showed the central regions well, with a bright elongated core region at 192x. The galaxy has a tiny companion, IC 879.

IC 879
A small companion galaxy of 5078, located around 3' SW. Now, this is where the performance of my 10" reflector completely shocked me. This galaxy is magnitude 14, which, in a NELM 4.5-5 suburban sky no 10" reflector is expected to pick up. On "NGCIC.org", an amatuer note of IC879 states that it was "not seen" with a 13.1" reflector. Upon careful, intent observation with averted vision at 192x, I kid you not, this galaxy popped into view!!! I estimate I could hold it in sight about 80% of the time. I kept observing it for a good 10-15 minutes, to really confirm the sighting. Man, I was the ecstatic. I just had to do a celebration jig which thankfully no one witnessed! :D:D:D I do believe that the flocked tube and the flocked dewshield played a major role in making this object at the absolute limit of visibility - visible.

NGC 5101
192x - A nice bright core enveloped in a fainter circular haze. Mag 10.7, SFC brightness a surprisingly low 13.9 (probably the average of the bright core area and the very faint outer envelope that is visible on images). A mag 12.6 star sits about 2' W of the core. The galaxy is located about 35' E of NGC5078.

NGC 5061
At 192x a bright, stellar core was visible surrounded by a fairly bright circular haze. Magnitude is a decent 10.5 but surface brightness only 13 but visually the galaxy is easier than the SFC brightness suggests. Located about 45' NW of 5078. A mag 13 star is embedded in the NE portion of halo.

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ABELL 3574
This is a galaxy cluster which is easily found about 3º NNE of the 4th mag star 1 Centauri. The cluster sits just within the Centaurus side of the Hydra/Centaurus border. Due to rapidly approaching twilight, I barely scratched the surface of what this whole region has to offer.

The following galaxies are members of ABELL 3574:

NGC 5291
Forms part of the "Seashell" galaxy pair. Now, once again, my sighting of IC879 is re-inforced here. This galaxy has a listed mag of 14.2, with an equally feeble SFC brightness of 13.9, which by all means should not have been visible with a 10" from my suburban sky. When, after careful observation, the galaxy manifested itself in my 192x eyepiece, I could barely believe it :eyepop: I increased the mag to 250x, despite the shocking seeing. This cluster of galaxies was riding the zenith so I had the best seats in da house. Stuff me, at 250x I could not only see the galaxy, which is only 0.3 mags off the theoretical limit of a 10", but I did make out a N-S elongation. Turning to the MSA, the symbol is indeed orientated in a N-S angle!

MCG-05-33-005
This is the so-called "Seashell" galaxy and is located adject to NGC5291's SW edge. I believe that this object is fainter than NGC 5291, which already tested my 10" reflector to the absolute limit. At 250x, I intently studied the area when an ultra-feeble haze emerged where this galaxy should be. Making use of averted vision, careful concentration and several minutes at the eyepiece, I was astounded to see this excessively faint ghost pop in and out of view. I estimate I could hold it in view about 50% of the time. I'm not sure of the magnitude as I couldnt find it listed anywhere, but I suspect it could be around the low-mid 14's! If anyone has the magnitude for this, please let me know! This is also my first NON-NGC/IC galaxy :D As I was excitedly checking the charts, I knocked the eyepiece which almost catapulted out of the focuser!! I had to re-tighten the focuser tension screws to hold the heavy Vixen and Barlow combo in place without the focuser slipping and slopping!

IC 4329
After the excitement of pushing the limits, it was time to plough on. This is the primary member of Abell 3574. At 192x, this galaxy showed considerable N-S elongation and was relatively easy to see with a listed mag of 11.3 and surface brightness of 13.2.

IC 4329A
192x - Located around 4' SE of IC4329. This galaxy appeared largely circular and smaller than 4329. Not sure of its magnitude, but comparing with 4329, I'd estimate it around 12.

NGC 5298
Located about 10' SW of IC 4329. Faint haze at 192x located between 2 faint stars. Slightly elongated E-W, mag 13.2, SFC brightness 13.0.

NGC 5302
192x - Brighter than 5298 at mag 12.3, SFC brightness 12.9. Located about 6' S of 5298, in same moderate power field. A N-S elongation was visible.

Drawing to a close
This is only my 3rd time hunting galaxies with my 10" reflector and I must say, its performance on galaxies has far exceeded my expectations. Never in my life did I ever think that I was gonna pick out 14th mag galaxies from my outer surburban, NELM 4.5-5 backyard. And to top it all off, the seeing was amongst the poorest I've ever experienced. I'd hazard that from a truly dark sky with great seeing, this scope could possibly get close to 15th mag :eyepop: All I know now is that Pluto doesn't stand a chance in hell ;) It'll will be interesting repeating this from a +6.5 sky. Sadly, twilight came before I knew it and I rewarded myself with a nice cup of coffee, excited about how far I could push my scope :D

I will include a sketch I made of the Sombrero Galaxy soon. Also included is a couple of pics of my observing setup in my backyard :) Basically I have the eypiece box, maps andsketch pad layed on the rug. Also seen in the pics is my state-of-the-art adjustable observing chair.

EDIT - included sketch of Sombrero Galaxy

[erick]

I hesitate to respond lest you be fast asleep by now and I wake you! You've obviously had several good nights, SAB. All your observation reports are printed out as targets for me. I only hope I can locate and see them as you have. Glad to hear you are having fun now we've had a run of cloud-free evenings. Always a good read - thanks!

[goober]

Great report - I always enjoy the read and I'm glad the weather cooperated with you. I can relate to dark adapting... when I got up at 3am, I put my red headlamp on and setup in darkness. I then made a cup of tea to take outside and blinded myself by opening fridge door ... :rolleyes:

Interesting setup photo - nice and simple - things I can relate to. Love the observing chair! In the past couple of months I've expanded from scope and stool, by adding an aluminium table that collapses down. That's been handy. I'm still trying to distill the setup into a perfect no-fuss system. I wish I'd watched PhilW break down and pack his dob at Kallista a few weeks ago - I swear it took him about 3 minutes!

Regarding how faint you are going with this scope... I'm beginning to suspect you have amazing eyesight. Your eyes are a third of the optical network when viewing something (along with the atmosphere and your optics).

[goober]

I did some digging over lunch (http://www.skymap.com/mcg.htm)

MCG-05-33-004 15.00 206.861 13 47 26 - 29 48 57.6
MCG-05-33-005 16.00 206.863 13 47 27 - 30 24 57.6

(Approximate) magnitude 16?

[§AB]

Thanks Erick and Doug :)

My eyesight is quite ordinary, nothing special!

Re MCG-05-33-005, Steve Gottlieb estimates the mag at around 15 http://www.astronomy-mall.com/Adventures.In.Deep.Space/ic4329.htm

Max visual limit for a 10" is often given as 14.8. With my flocked tube and dewshield, the galaxy's location virtually at the zenith and good transparency, 15th mag is possible IMO. It's tiny size would almost certainly imply high SFC brightness so perhaps that is the determining factor in its visibility at the eyepiece. Assuming it has a V=15.0, its SFC could be in the 14.5 range. In any case, there was definately the faintest possible haze wavering in and out of vision off the SW edge of 5291!

[Dave47tuc]

Mate a very enjoyable read thanks.:thumbsup:

Your observing skills are very good indeed.;)

[desler]

Thanks for the great read, The 10 inch seems to be working really well for you. I popped out for about 20 minutes last night here and found the seeing really good, being a newb and a bit obsessive, anything where I can see the sky at the moment is considered good. Sleep well!

Darren:)

[ngcles]

Hi §AB,

You're addicted aren't you?

Seriously, great report I enjoyed it thoroughly. Pushing your 'scope (whatever the 'scope) your eyes and the conditions to the limit is a great sport that I've also enjoyed for years. This is what _serious_ deep sky observing is all about -- irrespective of what size 'scope you are looking through ; 3 or 30". This ain't touring Paris in a sight-seeing coach, it is scaling the south-face of Everest!

I too rememberr the night I broke the 14th magnitude barrier with my 10" -- and I had the same reaction. But just a quick (well, quickish) note on (faint) magnitudes.

Once you get past about 13th magnitude, it's a bit like the "Pirate's Code" -- its more like a guide, and galaxy magnitudes (generally speaking) begin to get seriously rubbery once you pass about mag 14.5.

The problem lies with (1) Most faint galaxies haven't been photometrically measured and (2) the way the magnitude is measured or calculated and at _what wavelength_.

Most galaxies etc brighter that about mag 12 have been properly (photometrically) measured at a visual wavelength to provide a proper v magnitude. When you see a magnitude number prefixed or suffixed with a "v" you know it is a proper visual magnitude. Many others for good reasons have had their magnitudes measured at a shorter blue wavelength. This is usually indicated with a (B). The general rule with these Blue magnitudes is to add about 0.75 of a magnitude to get an _approximate_ v magnitude.

Others are prefixed or suffixed with a (P) this is a photographic magnitude and many are an estimate based on its appearance on a survey plate or other image. Some are reasonable estimates some aren't.

Once you get down past mag 14.5, very, very few galaxies have had accurate photometry performed at any wavelength and the magnitude given is somtimes (often) very much a guide (in many cases a "guesstimate"). And, the problem gets more acute the fainter it is.

I've looked at quite a few galaxies with my 18" with magnitudes said to be in the 17th and 18th magnitude range -- that shouldn't be visible at all, yet they are. It is the estimate that is incorrect or rubbery.

One example is quite near the Hydra I or Abell 1060 cluster you have observed. Just 1/2 a degree NE is a small group of galaxies surrounding IC 2597. In another catalogue it is called Hickson 48. The Hickson catalog are all very compact groups of small and faint galaxies.

There is an image here:

http://stdatu.stsci.edu/cgi-bin/dss_search?v=poss2ukstu_red&r=10+37+47.45&d=-27+04+54.1&e=J2000&h=15.0&w=15.0&f=gif&c=none&fov=NONE&v3=


From the image, the galaxies of Hickson 48 are:

IC 2597 Mag 12.8 (B) Hickson 48A (Centre)
ESO 501-59 Mag 15.0 (B) Hickson 48B (6 O'Clock)
PGC 31577 Mag 16.4 (B) Hickson 48C (2 O'Clock)
PGC 31580 Mag 17.0 ? Hickson 48D (1 O'Clock)


BTW, I _love_ Hickson groups!!

Now, IC 2597 under a dark sky will be very faint, but won't prove too much of a challenge to your 10". Surprisingly, you might also be able to see 48B in excellent conditions. Hickson 48C is visible in 31cm (and not too difficult) and using 46cm, all 4 are there. These magnitudes (B & C) are clearly (very) rubbery.

Passing on to NGC 5291, in the RC3, this has been assigned a B mag of 15.1and/or a v mag of 14.2, so you have done a truly outstanding job of pulling it in under a suburban sky. The close companion is MCG -5-33-5
which in the PGC (Principal Galaxy Catalogue) has been assigned a magnitude no less than 18! Yes 18, it isn't a typo. This is clearly, clearly wrong! I think you are right -- approx mag 14.2 to 14.3 is my guess.

That does not detract one jot from your achievement of having found and observed them -- they are very to extremely faint objects for 25cm particularly in suburban conditions -- well done!

Thought that was complicated? Now we move on to PNe magnitudes -- and that is a a _really_ complex topic (ie black art) ...

Best,

Les D
Contributing Editor
AS&T

[PhilW]

It takes a little more than 3 minutes - maybe 5 :D. There are just six large plastic nuts that unscrew by hand, & the trusses stay together as a unit (this latter point is key, otherwise you have loose poles rolling everywhere). I will post a pic of it tonight in Omaroo's 'show us your scope' thread on the ATM discussion so you can see how it folds up.

Also I used a lot of foam in its construction cos I am a weakling & don't like to lift heavy things, but I'll discuss that in the thread too.

Phil

[Karlsson]

Thanks for this explanation, Les!

It finally clears up an 8 year old mystery - when we accidentally stumbled upon UGC2902 in Per with my 8" Newt, admittedly from a very dark site in the Philippines, where we were living at the time (and amongst other things, in control of the street lighting... :D)

We had little access to resources, but what we could find was different magnitudes ranging from 14-ish to 15.9, but all beyond my scope's 'limit'... And yet it was unmistakable as it forms an almost equilateral triangle with two 8-ish mag stars, and there isn't all that much else to be found in that FoV... We were never able to repeat the feat, as the skies there may be dark but rarely completely free of haze.

When I read your post I went back to our observation records, and now I'm finally convinced we didn't see a phantom: peace of mind... :)

[§AB]

That's an excellent explanation Les, Thanks! I thought that the mag 15-16 figure for MCG -5-33-5 is completely suspect, coz if that were true, I wouldn't have seen it.

I posed the question on Cloudynights and one member has found the actual magnitude for MCG -5-33-5 ..... 14.7 (v), SFC brightness 13.9 :eyepop::party2: I think the flocking and dewshield played a major part in making these objects, which are at the absolute limit of a 10", visible from my suburban backyard.

So in theory, at a truly dark sky, my scope could pick out 15th magnitude stars and small concentrated galaxies similar to 5291/MCG -5-33-5.

Man, I'm completely hooked on galaxy hunting now! I had no idea it could be so rewarding!


Thanks Dave :) Your old scope is one fine galaxy workhorse! and its the first instrument I've used which shows Saturns Crepe ring on a regular basis :thumbsup: Cant wait till Jupiter gains some altitude....

[goober]

Just to add to the confusion, I looked it up in Uranometria Vol. 3 tonight - listed as 15.1 (v). :P

[ngcles]

Hi §AB,

§AB wrote:

"I think the flocking and dewshield played a major part in making these objects, which are at the absolute limit of a 10", visible from my suburban backyard."

It undoubtedly played a role, but much more importantly you are also using what I think is a "just right" exit pupil for maximum contrast on low-contrast, small deep-sky objects -- about 1.5 to 2mm. At x146 the ep is 1.71mm and at x192 1.3mm. :thumbsup:

My old 10" was "flocked" too. I read about the idea in the US magazine "Amateur Astronomy". Black flocking paper wasn't so easily obtained then so following the article I went to a haberdashery and bought 1.2m of German black cotton velvet.

Ordinary acrylic velvet is real shiny compared to this stuff which was about $100 per metre last time I looked and hard to find too. But it is _amazing_. Spread it out on the loungeroom floor and it just looks like a big black hole -- a void. It seems to swallow light. After taking some advice at the hardware, I used an epoxy glue to stick it on the inside of the tube. I rolled the velvet up on a long broom handle, painted a section of the inside of the tube with glue, laid it down using the broom and rolled it on like wallpaper smoothing it with hands. Paint the next section with glue, roll it down, smooth it out, paint the next section, roll it down, smooth it out etc etc. I did a really good job of it with only a couple of low bubbles here and there.

When my wife and I went to get up off the floor after having done the job, we discovered we were both stoned on the glue because we spent so much of the time with our heads in oppposite ends of the tube smoothing out air-bubbles! (true story). Co-incidently, this was the same experience the guy who wrote the article had, but I overlooked as a consideration.

When it came time to do the 12", I used wallpaper glue which also gave a good (but less intoxicating) result.

§AB wrote:

"So in theory, at a truly dark sky, my scope could pick out 15th magnitude stars and small concentrated galaxies similar to 5291/MCG -5-33-5."

I can't think of any reason it/you wouldn't. I believe the faintest stars I could (reasonably easily) detect with my old 10" were about 15.2 and galaxies with SB magnitudes a bit worse than 14 is about the limit in a truly dark sky. But don't accept my word on that -- push for your own limit because you just might do better.

§AB wrote:

"Man, I'm completely hooked on galaxy hunting now! I had no idea it could be so rewarding!"

Know the feeling!

But remember, there are many other equally big challenges out there, particularly in the G.Cs and PNe. On that front, I think you might find the Jul/Aug 2008 AS&T Deep Sky Delights will be interesting!

Best,

Les D
Contributing Editor
AS&T

[§AB]

got it right without even realising :thumbsup:


haha way to discover a legal way of getting high :lol: Nice one!

The flocking stuff in my scope is a black veleet material, which is black as and you cant see anything when u look down the tube!


15.2 is very impressive for a 10" scope. I'll have to get to a dark sky site, armed with data and maps for very faint stars and galaxies and really test the boundaries :)



Planetaries are my other favourite breed of deepsky. When seeing is good (rare), I usually throw all the mag I have at the scope to tease out their innards. The MSA plots an extremely high density of PNe around the Scorpius and Sagittarius, with some areas having up to 5 plotted in a single square degree :eyepop:Come winter, I'll have fun there :thumbsup: