sponsored by psychohistorian.org
RA: 08h 40m 40s
Dec: −53° 03′ 24″
Ch: MSA:981, U2:425, SA:25
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003), Corwin (2004)
Type: open cluster, 23m
Mag: B=?, V=2.5
Select a sketch and click the button to view
First recorded by Lacaille (1752, 1755) as a "small heap of stars."
Later (1835) listed as Brisbane 2148, "cluster".
IC 2391. There is certainly a cluster here, and it was certainly found by Solon I. Bailey during his survey of the sky on Harvard Patrol Camera plates. However, it is still not clear, without delving into the professional literature, just which stars belong to the cluster, and which are in the field around it.
Bailey made the cluster only 15 arcmin across and centered it on Omicron Velorum. Brian Skiff and AH make it 60 arcmin across and still center it on the star, though on the DSS and the IIIaJ film, this larger cluster is clearly centered about 30 seconds of time to the east and 10 arcmin to the south (I call this "IC 2391 all" in the table). I put Bailey's 15 arcmin core about 10 seconds west and 2.5 arcmin south of Omicron.
For now, you have your choice. I'll do some digging someday and report here just which stars are cluster members and which are not.
In the meantime, AH have a fascinating Note relating this cluster's part in an all-sky stellar association.
"UBV sequences in five southern galactic clusters" [http://adsabs.harvard.edu/abs/1960ArA.....2..379L]
"Summary: Photoelectric sequences in the UBV system are determined for the galactic clusters NGC 2422, IC 2391, IC 2395, Tr 10, and NGC 3114 by means of the Rockefeller reflector of the Boyden Observatory in South Africa."
"On some southern galactic clusters" [http://adsabs.harvard.edu/abs/1962ArA.....3...65L]
"Summary: Magnitudes and colours are determined for stars in the galactic clusters IC 2391, IC 2395, NGC 2470 [sic], Tr 10, and NGC 3114. Proper motions are used to determine membership in IC 2391 and Tr 10. The cluster properties are discussed."
Reports on an investigation of five southern galactic clusters (IC 2391, IC 2395, NGC 2670, Tr 10 and NGC 3114) which were "observed photoelectrically and photographically by the author during a stay in 1958 at the Boyden Observatory in South Africa." The 35.5-inch ADH Baker-Schmidt telescope was used, and the observers were Lynga, H. Haffner, and Bester.
Stellenbosch (Paradyskloof Rifle Range)
11x80 tripod-mounted binoculars (12.5-mm aperture mask)
Conditions: Dark moon. Slight easterly breeze. NELM approx 5.5 at the pole. Dew.
Coarse cluster of six scattered bright stars. Rough "W" shape, opening to the southeast. Not a small grouping, though poor. Some much fainter stars around and through the W.
2007 May 28, 22:20 SAST
Walmer, Port Elizabeth
2.5-inch f/7.6 refractor (EP: 25mm 28x 45arcmin fov)
Conditions: Slightly cloudy, stable atmosphere.
omicron Velorum Cluster. Difficult to find, once found, bright with 18 well resolved stars, nevertheless, its very big and spills out of 45arcmin field of view, being 50arcminutes in size with apparent magnitude M2.5. Lower magnification reveals large dark gaps towards the centre, 20arcmin in size. Main prominent stars east and west M3.2 are surrounded by equally spaced dimmer stars M5.6-M6; the range of brightness is fairly constant for the majority of the outer stars and the inner more prominent stars. Delta Velorum is south by one degree M2.2, the main field star in the vicinity.
The Messier objects
The Bennett objects
The Caldwell list
DOCdb is still in beta-release.
Known issues, feature requests, and updates on bug fixes, are here:
Found a bug? Have a comment or suggestion to improve DOCdb? Please let us know!
DOCdb is a free online resource that exists to promote deep sky observing.
You could help by sharing your observations, writing an article, digitizing and proof-reading historical material, and more.
Everything on DOCdb.net is © 2004-2010 by Auke Slotegraaf, unless stated otherwise or if you can prove you have divine permission to use it. Before using material published here, please consult the Creative Commons Attribution-Non-Commercial-Share Alike 2.5 License. Some material on DOCdb is copyright the individual authors. If in doubt, don't reproduce. And that goes for having children, too. Please note that the recommended browser for DOCdb is Firefox 3.x. You may also get good results with K-Meleon. Good luck if you're using IE. A successful experience with other browsers, including Opera and Safari, may vary.