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NGC 6647 (15,184 of 18,816)

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NGC 6647

NGC 6647, C 1828-173, VIII 14, h 2014, GC 4418

RA: 18h 31m 30s
Dec: −17° 21′ 0″

Con: Sagittarius
Ch: MSA:1367, U2:340, SA:16

Ref: SIMBAD

(reference key)

Type: open cluster

Mag: B=?, V=8

Size: ?
PA: ?

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

NGC 6647, H VIII 14, was also seen by JH whose position is adopted in NGC. There is nothing obvious at that position. WH's original position is about 8 arcmin west-northwest of his son's. Just 4 arcmin northeast of that is a group, about four arcmin across, of a couple of dozen stars. The brightest is around 12th magnitude. I think that these are the stars that WH took to be a cluster.

What I find curious about this object is the description. NGC follows GC exactly in calling the object a "Cl, L, Ri, lC, sts vS." How did JH get that out of his father's and his own observations? WH's description reads, "A cl of sc pL sts," while JH's reads "A very loose parcel of v small stars, hardly noticeable as a cluster." "Large" perhaps, but "Rich"? Perhaps JH penned the description in haste.

Whatever the case, the clump of stars that I believe to be WH's object does not match the NGC description, though it does fit what WH himself wrote.

Historical observations

William Herschel (c.1784)

Synonyms: H VIII-014

Discovered in 1785 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a cluster of scattered pretty large stars."

Published comments

Vorontsov-Velyaminov, B. (1925/1926)

Vorontsov-Velyaminov, B. "Integral magnitudes of south star clusters", Astron. Nach. 228, 325. Comparing the brightness of the cluster with the extrafocal images of stars, he estimates the magnitudes as 7.94

Melotte, P.J. (1915)

A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.

An open cluster of fairly bright stars. Resembles NGC 6494. Not in NGC; noted by Bailey. Possibly this is NGC 6647.

Sulentic & Tifft (1973)

(Sulentic and Tifft 1973) notes that this is a nonexistent object. Their coded description reads NO CL DC.

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