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RA: 20h 16m 30s
Dec: +37° 38′ 0″
Ch: MSA:1149, U2:119, SA:9
Ref: SIMBAD, DAML02, Archinal&Hynes (2003)
Type: open cluster, 23pn
Mag: B=7.87, V=7.3
IC 4996 is an apparent cluster found by F. A. Bellamy on a 13-inch Oxford astrograph plate. His article is devoted to the measurement of positions and magnitudes of 103 stars in an area of about 15 arcmin across more or less centered on the cluster.
Unfortunately, Bellamy does not explicitely give a position for the cluster, and that given by Dreyer in IC2 is about 25 arcmin off in declination. Searching around the correct position, I found a clump of faint stars arrayed around a bright double or triple star a few arcmin north. This looks like only a random field clump to me -- the area is littered with dust patches and faint traces of nebulosity.
Nevertheless, I've included the clump in the position table as the "core" of Bellamy's object. If some of the bright stars that he gives in his table really do form a cluster, then the entire thing is about 17 arcmin across.
Those interested in seeing just what stars Bellamy measured will find his article in MN 64, 662, 1904.
It is a member of the Cygnus OB 1 Association.
Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 6' and the class as 1 3 p.
Photo Index by Jim Lucyk: Deep Sky #23 Su88 p40.
MacRobert writes: "Here is an open cluster that escaped the notice of all the 19th century sky sweepers whose lists of objects became the NGC ... it is not hard to see once you know to look for it. An 8th mag triple star marks the spot. Use averted vision, and out of the dark background there gradually shimmers a spray of many more stars elongated north-south."
WDS: central trap = ADS13626.
15cm - not at all consp as cl @ 30x, but triangle eye-catching in vrich *fld.
at 80x averted vis shows f cl members while direct vis shows only
triangle and a few others---the `blinking' open cl! 165x: 20 *s in 3'-4'
diam, only one comp to star A vis, one to B occas vis. * due N of B at
threshold. comp nr B seems sl elong: may be combined light of both f
comps. delta-m for BC ~1.2; A fntst of triangle: delta-m CA ~0.75 (est
at 80x to minimizeinfluence of f comps). BS, 26Mar1988, Anderson Mesa..
25cm - 190x: consp triangle w/long base facing N, brtst * (m8) at obtuse S tip.
18 *s at threshold of vis spreading N and a little E from triangle.
30cm - interesting. four brtst *s on E edge, shaped like nice trapezium. rest
of cl sprinkled out to E, mostly m13+. total of about 30 *s in 3'.5
diam w/o condensation.
Observing site: Little Tycho Observatory
[20h 16m 30s, 37° 38m 0s] A wide triple near P Cyg. Quite nice, but not listed. White stars. Approximately 50 arc second sep.
The Messier objects
The Bennett objects
The Caldwell list
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