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RA: 16h 41m 24s
Dec: −48° 46′ 0″
Ch: MSA:1481, U2:407, SA:22
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 23p
Mag: B=5.34, V=5.2
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James Dunlop observed this cluster from Paramatta, New South Wales, and included it as No. 413 in his catalogue of 1827. Using a 9-inch f/12 telescope, he described it as "A cluster of small stars, with a bright star in the preceding side. A very considerable branch or tail proceeds from the north side, which joins a very large cluster."
Observed by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "Cluster VIII; consists of about a dozen stars 10..11 magnitude, and perhaps as many less, with stragglers, which fill field. In its preceding part is a fine double star ... and yet more preceding is a very large, faint nebula, in which the preceding part of the cluster is involved."
Ced 136b (NGC 6193)
Position (1900): RA 16 33.8, Dec - 48 34
Star: -48 11070 (Mp=5.0, V=5.35, SpT=Oe5)
Spectrum of nebula: emission spectrum (inferred from sp.t. of exciting star)
Classification: Neb associated with mainly one star (which may be multiple) - star surrounded by a neb envelope without conspicuous structure (eg. lambda Scorpii)
Notes: "Ced 136 Nebulous field discovered by John Herschel in 1836. Ced 136 b = The nebulous cluster NGC 6193 = GC 4224 = h 3642. FA 38. (194). The cluster = Dunlop 413. R. Principal star in the cluster: - 48 11070 = HD 150135/6 = Boss 22418/9. Alternative Class: A. 1."
Burnham writes that the cluster is "a remarkable and brilliant aggregation ... the brightest star is the visual double h4876 (HD 150136), an O-type giant ... the 7th magnitude companion at 9.6 arcseconds was discovered by Herschel in 1836, and has shown no definite change in separation or PA since that time ... the close companion, at 1.6 arcseconds, was first measured in 1878. Neither star has shown any relative motion since discovery ... There is also a 10th magnitude companion at 13.4 arcseconds in PA 160 , and a fourth star at 13.9 arcseconds in PA 15 , magnitude 11. The cluster measures some 14' across and has a total magnitude of 5.2.
Vogt. N. & Moffat, AFJ (1973), "Southern Open Star Clusters III." Astron.Astrophys.Suppl., 10, 135-193. [image, table]
"Although this cluster is defined to have a diameter of 16', we have measured only stars in the central region of diameter 4'. This increases the probability of obtaining member stars and suffices to determine photoelectrically the distance and age. We derive .. d = 1.36 kpc, earliest Sp = O8.
"Cat. of Open Cl. south of -45° Decl.", Mem. 17 Mnt Stromlo Obs.
The associated nebula is NGC 6188. The cluster is a member of the Ara OB 1 Association.
The RNGC (Sulentic and Tifft 1973) notes that this is a 5.5 mag open cluster.
Hartung notes "this straggling cluster needs a large field; it shows remarkable long curved chains and lobes of stars with a small group near the centre. The field is beautiful and makes a good demonstration piece which is still effective in small apertures and there is some faint nebulosity involved. The brightest star is a close pair (5.6, 8.5, sep 1.5 arcsec pa 20 deg)."
Sanford writes of it as "a scattered star cluster involved with faint nebulosity which is spectacular in long-exposure photographs.
Phil Harrington (1990, Touring the Universe through Binoculars) calls it a "rich open cluster of 30 stars, although binoculars may not show that many. The brightest cluster member is the quadruple star h4876, first catalogued by John Herschel. The system's primary sun is a 6th mag landmark to watch for when searching for the cluster. Unfortunately, its companion stars are either too faint or too close to it to be detectable in binoculars. To the southwest [lies] NGC 6188."
6cm - vsm, poor. 4-5 *s to NE of m7.8 *, incl two brtr ones. CBL, Slate Mtn.
1998-04-23/24, 11x80 tripod-mounted binoculars, Die Boord. Seeing good, transparency below average, dew. "B *, 9 mag NE. Due W = 7.5m, 10x the distance". [These rough notes don't make much sense. The impression is that there are only 3 stars seen; but the directions don't match up too well with U407, nor were they compared to the map at the eyepiece. Very shoddy observing...]
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