3 old/distant open clusters and 1 young one

[Martin Meredith]

I've had a good run of 6 clear moonless nights out of 10 and I've spent most of them observing open clusters. Monoceros in particular is well-placed and chock full of them (128), as is Auriga (99) and of course Cassiopeia (183). For those with a decent southern horizon, Puppis isn't far behind with 173. I seem to have clocked up 55 in 6 sessions (along with the inevitable sidetracks to nearby galaxies). Each cluster is different. I've adopted a strategy of watching individual subs in mono as they come in and then at the last moment switching to the coloured stacked version. It comes as quite a shock to see the vibrant tones appear on the screen.

On Saturday I focused on some of the older clusters, and last night on some younger ones. I must admit to developing a real fondness for the older clusters with their shimmering faint star fields. First up is Trumpler 5 in Monoceros, to be found in the north of that constellation, with a higher declination than nearby Betelgeuse. This is one of the oldest known open clusters, with an estimated age of 5 billion years. It is also a rich and not particularly faint cluster with over 500 suspected members, including a very red carbon star, V493 Mon, visible here just below and to the right of centre. Its distance is thought to be nearly 8000 LYs.

 

However, Monoceros contains an even older open cluster in its southern reaches, not far from Puppis. Berkeley 39 has an age estimated at 8 billion years, and at 15.5 million LYs is located at nearly twice the distance of Trumpler 5. It is the 8th oldest known cluster. (the red 'star' left of centre is a hot pixel I think...) The listed position is some way off in declination.

The most distant listed open cluster in the Dias catalogue is Berkeley 29 in Gemini, which is thought to lie at an incredible 48500 light years. This is relatively young at only a billion years. Who knows whether it will last for another 10 billion? It seems quite depleted to me (75 members) but that might just be the distance. Again, the catalogue position seems to be off by a few arc minutes of RA. 

The visibility of all these clusters is aided by being in the direction away from the galactic centre.

At the other extreme of age, one of the youngest known clusters that is convenient to observe at the moment is NGC 2244, at just under 2 million years old, lying at a distance of over 5000 LYs. This is the cluster embedded at the centre of the Rosette Nebula also in Monoceros. Normally I use linear brightness scaling when doing live RGB combination in order to preserve the 'correct' RGB colour ratios, but given the presence of the nebula in this case I used nonlinear scaling to capture both it and the stars. The effect is to add a blue-cast. (I believe this is because the scaling function preferentially boosts weaker signals, which in this case is the blue channel).

I read somewhere that although there are just over 2000 open clusters listed, this is a tiny fraction of those present in our galaxy; the obscuring effects of dust and the great distances presumably make the others hard to spot.

Thanks for looking!

Martin

 

[Dave In Vermont]

Very interesting entities you've located, Martin - thank you!

Please do carry on this great work. I'm hoping to finally set-up my equipment when the weather gets warm here in my neck-of-the-woods. Got all the gear - but the Weather Gods!

Starry Skies!

Dave

[stash_old]

"6 out of 10" clear nights 

[elpajare]

Fantastic work Martin, as always.

[Martin Meredith]

Thanks elpajare and Dave; I know, stash_old, but I think the run of good luck has now come to an end for a few days at least....

Martin