omicron Velorum Cluster

Image gallery

Remarks

First recorded by Lacaille (1752, 1755) as a "small heap of stars."

Later (1835) listed as Brisbane 2148, "cluster".

History and Accurate Positions for the NGC/IC Objects (Corwin 2004)

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.

Published comments

Lynga, Gosta (1960)

"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."

Lynga, Gosta (1962)

"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.

Contemporary observations

Auke Slotegraaf

2002 July 01

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.

Gary Lillis

2007 May 28

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.