Object of the Week February 9, 2015 – Biurakan 11 and 12 a pair of "mystical" open clusters

[Uwe Glahn]

Biurakan 11 (Byurakan 11) = Be 27, Lund 262, OCL 521, C0648+058
Open Cluster (III1p) – Monoceros

R.A.: 6h51m21s
Dec.: +5°46.1
Size: 2'
Number of stars in cluster: 25
Brightest star: 15vmag

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Biurakan 12 (Byurakan 12) = Be 26, Lund 261, OCL 520, C0647+058
Open Cluster (III1m) – Monoceros

R.A.: 6h50m16s
Dec.: +5°43.7
Size: 4'
Number of stars in cluster: 30
Brightest star: 17vmag

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Most of us though open clusters to be boring objects – easy for big aperture, only some brighter stars, no structure or other challenging details. But these peaceful candidates can also be different – like Biurakan 11 and 12.

The name “Biurakan” (or “Byurakan”) comes from the Armenian observatory (BAO). Some famous scientists like Markarian or Ambartsumian researched there. The history of the catalog is difficult to research, because of missing Russian scientific platforms like A&A in the US. The whole catalog consists of 13 cluster members. Unfortunately nothing is traceable about the missing cluster 6. Neither WEBDA nor SIMBAD found any entries. Cluster 1-5[6] were cataloged by Iskudarian 1959, cluster 7-11 also by Iskudarian 1960. No discovery entry or history again about clusters 12 and 13.

Nerveless the unique history all 12 clusters are exiting targets with lots of challenging objects like numbers 7 or 13 but all can be seen with 16” aperture (see my project – only in German).

Special target is the pair of Biurakan 11 and 12 which are only 15' distance in the sky. Both clusters are really tough and a challenge in mid size telescopes. Biurakan 11 is a little bit easier in 16” aperture and shows hints of mottling within the cluster. Maybe both clusters are visible in smaller aperture or shows stars in bigger aperture.

Martin Germano
link
Biurakan11_Biur12_1024.jpg

Give it a go and let us know!

[Ivan Maly]

Interesting targets, Uwe. It seems though that we won't have a single clear night this month for deep-sky observing. In his 1960 paper (link) Iskudarian writes that clusters 7-11 were discovered on Palomar prints and plates from their own 21-inch Schmidt. (The observatory has, I believe, a 1-meter Schmidt also.) He also positions clusters 8-11 beyond the dense disk of the Galaxy in the direction of the anti-center.

[Steve Gottlieb]

At some point I wrote in my observing database (perhaps copying from an online observing report) that "The Biurakan Clusters were discovered by Victor Ambartsumian, the director of Byurakan Observatory, located on top of Mt. Aragats in Armenia in 1949." When I took a look at a few in Mononoceros, my first response was "these look just like Berkeley (Be) clusters!". Then I realized they are ALL duplicated in the Berkeley cluster list!

Biur 7 = Be 31
Biur 8 = Be 32
Biur 9 = Be 30
Biur 10 = Be 28
Biur 11 = Be 27
Biur 12 = Be 26
Biur 13 = Be 34

-- Steve