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RA: 20h 23m 56s
Dec: +38° 31′ 24″
Ch: MSA:1148, U2:120, SA:9
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 23mn
Mag: B=7.3, V=6.6
It is a member of the Cygnus OB 1 Association.
In the Appendix to the 1912 'Scientific Papers of Sir William Herschel' this object is described as "1794, October 27, Is not sufficiently marked in the heavens to deserve notice, as 7 or 8 small stars together are so frequent about this part of the heavens that one might find them by hundreds."
Vorontsov-Velyaminov, B. (1925) "Catalogue of integrated magnitudes of star clusters", Astron. Nach. 226.195. Comparing the brightness of the cluster with the extrafocal images of stars, he estimates the magnitude as 7.13.
Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 7' and the class as 3 3 p.
The RNGC (Sulentic and Tifft 1973) notes that this is a 9.0 mag open cluster.
"NGC 6913 .. is a young open cluster harboring O-type members and lying close to the plane of the Galaxy... Despite appearing in the Messier catalog as M29, few papers in literature deal with it, furthermore showing some disagreement in the results."
Cluster distance estimated range from 1.1 kpc to 2.2 kpc; "Tifft (1958) suggested that NGC 6913 is indeed the result of two separate groups of stars, one at 1.6 kpc and the other somewhere between 1.9 and 2.4 kpc."
Estimated ages span from 0.3-1.75 Myr to 10 Myr.
Reference: Boeche, C. et al. (2003) Kinematics and binaries in young stellar aggregates. II. NGC 6913=M29. arXiv:astro-ph/0310090v1
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "7M; 7' diameter; 20-plus 8 thru 11M members; all blue-white; 7 brightest stars form 2 opposing, symmetrical curves; cluster N6910 (6.5M; 8' diameter) 2 degrees due N; 25' NNE of 3M Gamma CYG; surrounded by 2-part nebulosity I.1318; cluster I.1311 2 degrees W of N6910; reference-VADSS-217."
MacRobert writes: "M29 is arranged in a unique shape. Seven of its brighter stars form two small arcs bowing toward each other like the outline of a power plant's cooling tower. There are supposed to be 50 stars here, but I certainly don't see that many with my 6-inch. What is apparent, however, is that this whole region is heavily obscured with dark clouds blotting out patches of the Milky Way background. Suspicious dark zones lie just east and north in particular."
Observer: Lew Gramer; Your skills: Intermediate; Date and UT of Observation: 1997-07-25/26, 04:00 UT; Location: Medford, MA, USA (42N); Site classification: urban; Limiting magnitude: 5.8 (zenith), intermittent haze; Seeing: 5 (out of 10 highest) - mediocre; Moon up: yes, 50% (not visible at site); Instrument: 7x50mm Simmons binoculars
Distinct bright haze just 1/2 a binocular field (less than 3o) SSE of gamma Cyg, and about 40' due W of a mag. 6 star, which is found immediately SE of gamma. Unmistakable, even in this sky! Diffuse, with no concentration apparent, although a stellaring of near-resolved stars was visible on the S edge.
6cm - sm, pretty cl of br *s. 12 *s vis w/a little haze. six brtr ones. immed fld is pretty blank.
7cm - sm sparse cl w/only brtr *s, not real well sep from fld @ 30x. 75x: 15 *s in 5' diam, mostly m8-9. BS, 27Nov1992, Anderson Mesa.
15cm - H shape suggested 15 *s. elong SE-NW, 8' diam. fairly distinct from fld by compactness and geometry.
- sparse isolated by dk Rift to E. many more bkgrnd *s starting at W edge of cl. 140x shows 25 *s in 4'-5' area incl six of m7-8. BS, 15Oct1990, Anderson Mesa.
20cm - kind of sm. esembles M18; a few br *s upon a rich fld. 20 *s m8-10 in 10' area.
25cm - sm and loose w/only a few br *s. box shape outstanding w/other pairs and shapes.
- 90x: 26 *s in 6' area.
30cm - 21 *s in 10' area. six brtst *s are in two arc NE&SW, concave outward like so: )(. br part of cl 6' across.
Observing from Stellenbosch, 1983, I used a 2-inch refractor and wrote: "Two bright stars involved. Brightest star double; secondary faint and close. Other stars in cluster difficult to see; with averted vision 2 or 3 stars can be glimpsed to sparkle out. Very difficult -- nebulosity around bright star." The size was estimated as 9'.
Alldays (22.50S, 20.12E, 770m).
12-inch f/10 SCT (95x, 218x)
Cluster eight stars are arranged in the form of a backwards "K". This lovely handful of stars is very boxy with the southern part more define and busy. 5.5' more or less in size.
The Messier objects
The Bennett objects
The Caldwell list
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