Rup 106 & E3

[Rob_K]

Continuing the quest for ever-more impossible globular clusters in a cheap 4.5" scope... :lol:

Anyway, last night we had our monthly club observing night out at the Porepunkah airstrip, and were greeted with great skies. Tons to see, cruised all the biggies, some fantastic views.

I came prepared with charts for globular clusters Rup 106 and E3, both well-positioned. Try as I might, I couldn't get a hint of anything at the E3 position, no surprise there.

Rup 106 was a different matter, and I'd like to get some advice on this from people who might have seen it before. Because it seemed relatively easy to me (compared to some impossibly faint things I have chased down LOL). I first looked when there was still a hint of brightness in the sky (just to nail down the position) and there was nothing there. A bit later, in dark sky, a very faint background glow was visible in the position, perhaps 4 arcminutes in diameter. I could hold it quite well, knocking the eyepiece and moving the field with the hand control. It never quite assumed a proper form, bits of it flickering in and out. Conditions were excellent - two mag 6.4 stars close to it were easy naked-eye. I checked the position again later as mist was starting to rise and there was nothing there again - amazing the effect of a bit of moisture in the air.

I've attached a rough sketch of what I was seeing - the 'glow' I've drawn is considerably exaggerated of course, it was a ghost of a ghost! In hindsight, I should have 'commandeered' one of the bigger scopes on the field to check it out, but I'm that used to observing on my own it didn't occur to me. :rolleyes:

Comments, advice welcome!

Cheers -

[Paddy]

Nice one Rob. I've not looked for this one before but your sketch matches what it looks like on Wikisky perfectly. If I get some observing in tonight I'll have a go.

What does E stand for? Might have a go at that one too.

As always, impressive what you achieve with the Tasco 4.5! I dips me lid.

[Rob_K]

Thanks Patrick!



E3 (ESO 037-SC001 = C0921-770) was one of three star clusters found on ESO blue plates in 1976, so I presume the E stands for "ESO". :shrug: E2 was an open cluster (in the LMC halo), while E1 & E3 were globular clusters. But E1 was later found to be identical with globular cluster AM1.

E3 should be well-gettable with your scope. It's nominally vis mag 11.4, but it's large and very diffuse. Good luck - post a report!!

Cheers -

[Rob_K]

Oops, I should have added that this isn't the first time I've tried for Rup 106 in the 4.5". First time there was nothing there, but in 2008 in pretty good conditions (but not as good as last night) I had tantalising glimpses of "something" but nowhere near enough to convince me that I had seen it. Strange how time gets away and it's three years later before I try again! :lol:

Cheers -

[pgc hunter]

Well done Rob. You've certainly milked that Tasco to no end :thumbsup: Try using a dark shroud over your head when hunting such faint objects. I find it helps alot.

[Rob_K]

Thanks pgc! Well, someone did hunt up a report of Rup 106 observed through a 110mm x 805mm newt - similar observation to mine except that I appear to have seen more of it. Just need those 'magic' dark nights, bit like the legendary 'perfect seeing' nights! Pretty comfortable adding it to my MW globular cluster list now. 105 & still counting! ;) :lol:

Cheers -

[pgc hunter]

I'm a firm believer in the ability of an observer to see difficult/extremely faint objects through relatively modest apertures, the difference is you gotta know what you're doing and how to make the most of the scope and conditions :thumbsup:

Legendary seeing eh...as far as Melbourne is concerned this failure of a season, the ability to resolve stars into pinpoints at anything above 100x is to be considered legendary :lol::screwy:

[Brian W]

Rob, I thought I was a minimalist using an 8". I may just have to dig out the 4.5 again.
Brian

[ngcles]

Hi Rob,

Yep the sketch shows a good position for Ruprecht 106 and I think it would be barely visible in 10.5cm given top quality skies and moderate magnification. I didn't find it hard at all in 25cm and here's my note from Bargo in 1996:

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.

The V-tip magnitude (brightest AGB member stars) for Ru106 is given as 14.8 so it isn't out of the question that some of the stars I saw were actual resolved member stars

E3 is a somewhat different bucket of fish. It is a very faint object for 30cm class 'scopes and still not particularly straightforward in larger ones.

I happened to look in on both last weekend up at Mudgee. Ru106 appears partly resolved in 46cm with maybe a dozen faint stars in the mags 14.5-16 range scattered over its LSB face that appears about 2.5 arc-mins across.

E3 even under a sky with an SQM-L reading of 21.55 was a sizable faint blur approaching 3.5 across that looked a little patchy or perhaps grainy but not resolved. In 50cm it appears to have raggedy edges.

Both show little to no concentration to centre.

Hope this helps.


Best,

Les D

[Rob_K]

Thanks Les, greatly appreciated! Yes, I didn't have any real expectation of seeing E3. I would still like to have another go at Rup 106 under the very best skies - just a tiny niggle that I seemed to see more than what is actually there. I'll also 'commandeer' a bigger scope if I can to double-check. Need some 'drought skies' - there's still so much moisture in the air that it has to affect observation, even when skies are dark.

There's still a couple more very faint globulars on my list, not presently well-situated for viewing... ;)

Cheers -