Globular Clusters

[Rob_K]

Less than perfect conditions tonight re transparency & light adaptation (damn computers!), but I ventured outside this evening to see if I could spot Pal 8 in the 4.5" reflector (using 21mm ep). It's there alright, but never more than a very dim, small roundish glow - very difficult when I first went out (no surprise!) but more clear later. Not easy like Pal 9, but nowhere near as difficult as Pal 7.

Seeing I was out there, had a go at a few others, E3, Rup 106 & Pal 12. E3 & Rup 106 were quite low, and unfavourably placed with respect to the town lights. Nothing at Rup 106 position, but a hint of something at E3, enough to encourage me to have a go under more favourable conditions. Tried Pal 12 just for the reason I have a shot showing some density & central brightening. Found the exact position and saw what appeared to be the little triangle of stars near it, but hadn't realised just how very, very tiny & faint this little triangle is. There was the vaguest hint of something there at times, but nothing I'd remotely call a sighting. Suspect higher power (only using 43x) and a lot more light needed! Anyway, it was an interesting hour or so!

Cheers -

[ngcles]

Hi Rob,

Though it is good to see you having a go, I'd be very, very surprised if you manage to see any of these in your last post. For the record here are some observations of them using a variety of apertures from 10 to 18". They were all made from either good rural sites with a ZLM of about 6.2, and some at an excellent site with a ZLM of about 6.5.

Rup 106 (10")

x86 34' TF. x171 17' TF. Not a particularly difficult object. Found in a field of nearly innumerable *s, 2 deg S of Gamma Centauri. Appears as an unresolved fairly sizable milky glow perhaps 2.5' diameter. Seems to have several faint superimposition *s about mag 14. Mag 9 * to the S by 3'. Scattered mag 13-14 *s like the sands of the beach.

Rup 106 (18")

x111 45' TF
x139 56' TF

Ru 106 Globular Cluster
RA: 12h 38m 40.2s Dec: -51° 09' 01"
Mag: 10.9 Mag V(tip): 14.8 Mag V(HB): 17.8
B-V (tip): --- Size: 2.0' Class:
R.V.: --- Source: Archinal *

This cluster is quite close to a mag 9*, 3' away to the S as a quite diffuse, hazy, galaxy-like looking object perhaps 2.0 -2.5' diameter with several faint stars scattered over the top. These may be resolved *s but are just as likely field stars at about mag 14.5. Appears to brighten broadly and slightly to centre without core or pip, 3' diameter hazy, background does not seem granular. Profusely littered field.

E3 (18")

x185 27' TF x247 20' TF

E 3 Globular Cluster *
RA: 09h 20m 59.3s Dec: -77° 16' 57"
Mag: 11.4 Mag V(tip): --- Mag V(HB): ---
B-V (tip): --- Size: --- Class: R.V.: ---
Source: Archinal

A quite faint GC but looks differrent at lest from my memory of in in the 31cm (no specific notes on this) quite faint pointed at from the E by 2 *s, mags 10 & 8 the closest is the latter 13' away E. A large 2.5' diameter diffuse and weakly grannular glow of lowish SB with a few (apparent superimposition *s) faint *s virtually no concentration to centre. No apparent resolution. Ragged edges. Nicely populated field considering it is Chamaeleon.


E3 (20")

x277 18' TF. Mag 11.5 Size 5'. Not difficult at all, indeed this object was discovered to be visible even in my own 31cm a short time later. To the W of a mag 7.5 * by 15', Appears perhaps slightly elongated roughly N-S, 1.5' x 1.2' with a moderate broad concentration to the cetnre with no evidence of resolution . Est cc 9-10. An easy D.V target in 50cm, It can be held steadily though it is very faint in 31cm with A.V at x186.


Pal 12 (10")

x181 17' TF. Mag 11.7 Size 2.7'. Found to the N of a small group of 3 *s in a Tri + 1 about mag 13.5. Very faint but not invisible, though it is barely detectable with D.V. Quite small looking like a weakly concentrated eliptical type eg. Weak to slight broad central brightening. No resolution, est cc 10.

Hope this helps,


Les D

Contributing Editor
Australian Sky & Telescope

[Rob_K]

Thanks Les - great information! All these are on my "don't bother" list anyway, but I just felt it would be interesting to have a look. I'll try UKS 1 next (just kidding - only a metre or so short in aperture!).

I'm pretty much at the end of my journey except for the two that haven't presented me the opportunity yet (6229 & 2419). Then I can start all over again! Thanks for your help

Cheers -

[glenc (Glen)]

Here is a map for finding a mag 13.7 globular in M31.
http://deepsky.astroinfo.org/And/g1/index.en.php

[glenc (Glen)]

This is a good website for globular clusters.
http://gclusters.altervista.org/

The most distant galactic GC is AM1 at 123.3 kpc (402 klyr).
The most distant galactic NGC GC is NGC 2419 at 82.6 kpc (269 klyr).

The faintest galactic NGC GC is mag 12.4 NGC 6749.

[glenc (Glen)]

I looked at more than 40 GC last night with a 16" Dob and a 13mm EP.
The most difficult one was NGC 6540.
http://dso-browser.com/dso/info/NGC/...=-5&min_alt=20
Other faint ones were NGC 6256, NGC 6380, NGC 6539 and IC 1276.
NGC 6380 is the faintest of these four.
https://picasaweb.google.com/1100488...94326912276690

[glenc (Glen)]

I have seen 79 globular clusters in the last 3 nights with my 16" Dob.
Has anyone seen NGC 6749? I looked for it this morning but did not see it.
https://picasaweb.google.com/1100488...95799439293970

Here is Steve Gottlieb's description.
"18" (8/2/11): this difficult NGC globular is highly obscured and just stands out clearly from the rich Milky Way background glow. At 225x it appears as a very faint diffuse glow, roughly 2' diameter, with a low surface brightness. A 12th magnitude star is superimposed and the slightly brighter core of the globular is located about 45" SW of this star. The edge of the globular is not well defined but appears to just reach a mag 12.5 on the south end. Additional mag 11-12 stars are clearly off the east, west and south side of the halo. Located 26' ENE of mag 5.8 HD 177178. "
http://www.cloudynights.com/ubbthrea.../o/all/fpart/1

[glenc (Glen)]

Star clusters and how to observe them By Mark Allison

http://books.google.com.au/books?id=...usters&f=false

Lots of interesting info on GC.

[astrospotter (Mark)]

first off thanks Glen, Les and Rob and others for a very nice read in this thread. I like globs a lot.

This is a bit embarrassing to post after the SteveG excellent observation but in the spirit of answering the question who has seen Ngc6749 and in what conditions, here goes

From 2700 feet at lat +36 (central California, USA) with SQM 21.0 (not real dark) in an 18" dob at 188x. This was in 2008 and I promise that since then I have improved a lot in my observational details . So this one is worth a re-visit this summer.

No resolution, size hard to judge. Position by careful star hop. Glow only

[Paddy (Patrick)]

Wow, you're really stacking away the GCs Glen! You've read my meagre notes on this faint little glow already - interesting to read how much an observer like Steve can get out of something so elusive!

[glenc (Glen)]

Yes I read your note Paddy, thanks. There seems to be a shortage of keen observers like you in Oz.
NGC 6749 is higher in the sky for Steve and his scope is bigger.

[glenc (Glen)]

Thanks Mark, I observed from California in 2006 with Kent Wallace but did not look for 6749 then.

[glenc (Glen)]

IC 1257 is one of the faintest NGC/IC globular. It is near M14.
Here are some descriptions from Steve Gottlieb.
http://www.astronomy-mall.com/Advent.../steve.ngc.htm

IC 1257 = OCL-51 = Lund 751 = Ced 144
17 27 08.5 -07 05 35
V = 13.1; Size 1

18" (7/26/06): picked up at 225x, but viewed at 325x as a very faint, low surface brightness disc of 30" diameter with only a very weak central brightening. This challenging globular was visible steadily, even with direct vision but there was no hints of details. A couple of mag 16-16.5 threshold stars are close S and W.

18" (7/18/04): at 250x, appeared very faint, very small, round, ~0.5' diameter. With direct vision, this globular is weakly concentrated to a faint quasi-stellar or stellar core. Visible continuously without much effort, though very unimipressive as a globular.

17.5" (6/30/00): at 280x this small low surface brightness globular appeared very faint, round, ~30" diameter but visible with direct vision. Appears to have an extremely faint knot at the south edge and a slight central brightening.

17.5" (7/27/95): very faint, round patch, ~1' diameter. Appears similar to a 15th magnitude galaxy with no hints of resolution or central concentration. Can hold steadily with averted vision. Located 5.8' W of a mag 11.5 star. Discovered to be a globular in 1996.

13.1": not found.

[Gem (Grant)]

Running a bit faint for some of us... need to get that 16" dob my wife promised. Just need to sort out imaging first though... which is time consuming!

[glenc (Glen)]

The attached list contains 50 bright globular clusters.
The faintest GCs in this list are M56 and NGC1261, both have mag 8.3.
NGC4372 has the lowest surface brightness (20.6).
M54 contains the faintest stars (horizontal branch mag 18.2) and it is also the most distant GC in this list (86,400 light years).
Explanations for the columns are at the end of the list.

wikisky.org images with a 28 arcmin field are at
https://picasaweb.google.com/1100488...COTv9cm0msHbSQ

[Paddy (Patrick)]

Another very useful list Glen.

[Gem (Grant)]

I can vouch for the usefulness of lists like this!

I have been working through a similar (but longer) list of the brightest globs. Lots of fun!

Just can't find the list at present (with the ticks on it to know which I have done... it was in the spare room but now one of the boys has moved in.... no hope of finding it now!)...

[Gem (Grant)]

Found the list!!

48 out of the top 50 (missing M92 and M68).
79 out of the top 100.
The top 100 by magnitude takes you down to 11.0 (not allowing for surface brightness).

All done with 9.25 or 10 inch scopes... and still trying!

[glenc (Glen)]

Well done Grant!

[andyc (Andy)]

I've got to thank you for all these interesting lists Glen - they make for some fine observing challenges . I'm up to over 50 globulars in total, though I have the benefit of having lived in both hemispheres with an 8" scope, but most globulars are southern ones anyway!