Five Berkeley clusters in Auriga

[Martin Meredith]

I had a chance to observe a further 11 Berkeley clusters on Monday, all in Perseus and Auriga. Here are 5 of them, all from Auriga, which itself contains 8 Be clusters. They display some subtle differences as reflected in their Trumpler classifications. In the main I used a minute each in LRGB, in 15s subs.

Berkeley 71 is an obvious cluster and the RA/Dec values are in the right place for once. This is a Trumpler-class 2-1-m-* cluster, meaning 'detached, slight concentration; most stars of the same brightness; medium rich'. Be 71 is one of the 3 clusters studied in this article: http://articles.adsabs.harvard.edu/pdf/2004BASI...32..371L

There are some interesting stars and groupings in the surrounding field. At around 1 oclock outside the cluster itself is a rather red Mira-type variable, ranging from 12.2 to 14.1 over a 145 day period. At around 3 oclock is a colour-contrast close pair with similar magnitudes (no data as to whether this is just a visual alignment), and near the base at around 5 oclock is an unequal pair of nearly white and orange stars.

 

 

Berkeley 69 (just below-right of centre here) is somewhat similar in appearance, with a Trumpler classification 2-2-m-*, differing from Be 71 in having a medium range of brightness. This cluster is just a degree or so SE of the much larger open cluster NGC 1893. Be 69 is described in more detail here: https://aas.aanda.org/articles/aas/pdf/1997/04/ds1154.pdf

 

 

What about Berkeley 70? This one isn't as clear cut as the earlier two, with a classification of 3-1-m-*, the initial 3 meaning  'detached, no concentration' (I sometimes know the feeling...)

There is something of a denser stellar field NE of the centre (E meaning left) -- actually more like a river of stars. Archinal & Hynes report a comment that this may not be a genuine cluster. However, more recent studies suggest it is indeed a cluster e.g. see https://arxiv.org/pdf/1207.3244.pdf and that it contains a number of blue stragglers. When I complete the Berkeley catalogue I intend to check with GAIA-based studies for all the Be clusters to see what the latest state of play is. 

 

Berkeley 19 is different again. This is a very faint but rich (~150 stars) grouping in the centre of the shot. Perhaps surprisingly, it has the same Trumpler class, 2-1-m, as Be 71, but then the classification scheme appears not to distinguish overall cluster brightness.

Really, it needs a longer exposure to bring out more of the colour. I've said on other occasions that I really like these faint clusters. In part it is for the same reason as I like their much more distant 'visual cousins', the Shakhbazian galaxy clusters (I just read that SHK 1 has been mistaken for an OC in the past, and its easy to see why). 

This one is faint because it is one of the more distant OCs known (an older estimate is around 26000 light years; but GAIA might have updated that). Be 19 is one of two clusters described in this article http://articles.adsabs.harvard.edu/pdf/1984ApJ...286..552C

 

Finally, here is Berkeley 17, class 3-1-r. The richness (~100 stars) is perhaps hard to see in this shot (a little easier in the negative view). The second most interesting thing about this one is the line of very red stars running near-horizontally across the centre of the cluster (some or all may be field stars).

 

 

 

But what's really interesting about Be 17 is that it is the oldest known galactic cluster, with an age of around 10 billion years (unfortunately I wasn't aware of this when I observed it otherwise I would have given it more respect (and photons)). As such it has been much-studied. This very recent article is dedicated solely to Be 17 which I look forward to reading soon. https://arxiv.org/pdf/1902.05891.pdf .

Thanks for looking

Martin

 

[Mike JW]

Always enjoy seeing the Berkeley Clusters (and in colour). Re 71 and the pair of stars at 3 o clock - line of sight.

You should really gather up all your Berkeley shots/notes into a single thread - would make for a useful resource.

Good idea to mention the Trumpler Classification - I use to test myself when looking at cluster visually - I rarely got it right compared to the official designation.

Mike

[Martin Meredith]

Hi Mike

I was taking 'stock' (OC aficionados will have to excuse the pun) last night and although I've observed 87 of the 104, some are in mono and others are quite poor, so in reality I have about 20 to go.

My plan is to produce a document of some kind recording all the Berkeleys once I've finished them, and try to relate them to the GAIA data release and recent research on which are likely clusters, etc. perhaps organising them in a 2D grid by Trumpler criteria. And of course to correct the RA/Decs.

Martin

[Mike JW]

Looking forward to the document.

Mike