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RA: 07h 08m 18s
Dec: −13° 11′ 0″
Con: Canis Major
Ch: MSA:297, U2:273, SA:12
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 23r
Mag: B=8.58, V=7.7
Discovered by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "a pretty rich cluster, irregular figure, 7' diameter, gbM, stars 10..14th mg, place that of a double star, the chief."
Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 11' and the class as 2 2 pU.
The RNGC (Sulentic and Tifft 1973) notes that this is a 8.0 mag open cluster.
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
Raab, S. (1922) A research on open clusters. Lund Medd. Astron. Obs. Ser. II, 28, 1.
Discussed, based of F-A plates.
Moffat 1974: cen line of three: V=10.4,12.4,12.8. pairs: V=10.4,12.4; 12"; pa240, and h3930: V=9.9,10.9; 16"; pa80.
6cm - 13 *s trail away S and curve a little W from a m7.5 *. some f haze.
15cm - partially res @ 50x w/neb appearance. 140x: 8'-10' diam concen on E side, lots of stragglers extending SW. on N side of main grp is wide pair: 9.5, 10; 12: pa70. in center of concen is close line of three, cen one brtst, m11.5; line is only 10" long. BS, 20Nov1988, Anderson Mesa.
25cm - med size. one outstanding *. loose cl grouped irreg. 15' diam, 30 *s.
- cen part in diamond *ism, one being a pair (dm 1.5). outstanding * is N.
- mod consp. elong NE-SW in pa30, sev m9-10 *s scattered around. core is flattened and more sharply defined on E, dk area further E. nr edge of this is a sm nuc of ~8 *s, incl a pair (10.4,12.4). to N is wider pair (9.9,10.9) nrly parallel in pa45. 10'x6' area holds 30 *s. *s in nuc are m12-14. BS, 25Jan1982, Anderson Mesa.
30cm - 50 or so *s in 12'x8' cl elong NE-SW. 10" pair on N. SSE 2' of cl is 30" knot of ten *s incl close pair on its W side.
Steve Coe, using a 17.5" f/4.5, notes: "pretty bright, somewhat compressed, arrowhead shape points to starless region. Star at tip of arrowhead is double. Pretty rich cluster at 150X."
A 10-inch f/5 at 30x shows that the brightest star is an 8th mag primary lying on the northeastern edge of the cluster. The other members form a lobsided V, pointing north. This V is made up of seven or eight 9th mag and smaller stars. This striking V-shape is quite noticeable and prominent. The long arm of the V runs southwest from the bright star in the northeast; if you follow this bearing for about three-quarters of a degree and then look slightly east, you will see a very eye-catching curved arc of six 11th mag stars.
Using the 10-inch on a second occassion, I saw this V-shape as three converging lines made up of 10 or so pretty faint stars. At 120x the cluster shows about eight stars of 10th mag; sprinkled amongst them are fainter stars, resulting in a nebulous haze. The cluster lies between an 8th and 9th mag star. Three-quarters of a degree due south is a very striking curved row of about seven 10th mag stars.
Observing site: Little Tycho Observatory
[7h 8m 18s, -13° 10' 0"] A lackluster group of ~15 stars, 9mv... There is a pair in the center, 10", 65° pa.
Location:Blesfontein Guest Farm,Sutherland.
Sky Conditions:The most crystal clear sky possible.Dark moon and stars magnitude 6 and fainter are visible with the naked eye.Excellent clean sky,limited star flickering and brilliant objects.
This open cluster stars has an irregular appearance where I have counted 25 stars within a fixed diameter.There are bright and faint stars mixed together in this cluster which consists of 11th-13th magnitude stars.The stars in this cluster is well detached and that they are separated from each other.This open cluster measures 35.6'x 27.3'.Chart No.94,NSOG Vol.1.
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