Coathanger Cluster, Brocchi's Cluster (Collinder 399)

Object Description

Cr 399
Cr 399: Upside down Coathanger with open star cluster NGC 6802 on the left. Excerpt from the colored DSS [147]

The Coathanger (Collinder 399) is a loose star cluster. As luck would have it, ten stars 6th to 7th size class grouped together in a shape that resembles an upturned coat hanger.

Records of this cluster go back to the 10th century when the Persian astronomer Al-Sufi referred to it as a small cloud. Around 1000 years later, in 1903, it was mentioned in the «Communications from the Royal Wroclaw Observatory». But it was not until 1931 that the Swedish astronomer Per Collinder added the Coathanger to the group of open star clusters. Collinder summarized the open star clusters known at the time in a catalog as part of his dissertation and listed it as the 399th object. His catalog, which contains a total of 471 open star clusters, is based on the survey of the Franklin-Adams maps, the NGC catalog and its extensions, as well as the catalogs by Bailey, Melotte, Raab, Shapley, Trumpler, etc.

It is often doubted whether Cr 399 is a real star cluster and yet the number of members is often given in the literature as 40 or more stars. In 1970 Hall and Landingham examined the stars in the area of this cluster for mutual and movement. However, they came to the conclusion that only six bright stars are physically connected and that no weaker stars belong to them either. According to her, the cluster is around 200 million years old.

At the end of the 1980s, Pavlovskaya and Filipova studied star clusters that move together in space. They came to the conclusion that Cr 399 and about 10 other star clusters form a group. This group includes NGC 6633, 6709, 6882, 6885, IC 4665 and the Pleiades.

The Coathanger cluster is about 300 light years away and is moving towards us at about 18 km / s. He stands in front of a dark cloud, which he partially illuminates. The southern tip of the hook is formed by the 5.3m star 4 Vulpeculae. Only 19 arcseconds away from this is an optical companion with a brightness of 10 magnitudes. [93]

Name : Cr 399: Coathanger Cluster
Typ  : Offener Sternhaufen
R.A. : 19h 25m 24s
Dec. : +20° 11' 00"
Mag. : 3.6m
Diam.: 60'
No.* : 40
Br.* : 5.19m

Sometimes Cr 399 is also referred to as Brocchi's Cluster. The name finds its origin in the 20s of the 20th century. At that time, the American amateur astronomer D. F. Brocchi made a map of Cr 399 for the purpose of calibrating photometers. [93] Occasionally the name «Himmelsfähnchen» (sky flag) is also to be found among the German speaking amateur astronomers.

NGC 6802

NGC 6802
NGC 6802: 30'x 30' Section of STScI Digitized Sky Survey [160]

The open cluster NGC 6802 can be found in the shadow of the Coathanger Cluster, which is much larger in apparent diameter. The small but dense open star cluster of about 50 stars was discovered by Wilhelm Herschel with his small 6.2 inch reflector telescope on 22 September 1783 and cataloged as WH VI 14. The cluster is located east of Cr 399 and has a diameter of about three arc minutes. The brightest stars are about 13 mag, but the overall brightness is 8.8 mag. [22, 277]

Revised+Historic NGC/IC, Version 22/9, © Dr. Wolfgang Steinicke [277]
DesignationNGC 6802
TypeOCL (III1m)
Right Ascension19h 30m 36.0s
Declination+20° 15' 42"
Diameter5 arcmin
Visual magnitude8.8 mag
Metric Distance1.124 kpc
Dreyer DescriptionCl, L, vC, E 0°, st 14…18
Identification, RemarksOCL 114

Finder Chart

The two star clusters are very easy to find, because the larger of the two can be seen with the naked eye on a dark night. Both are about eight degrees south of Albireo (β Cygni) in the constellation Vulpecula. One can orientate oneself by the small constellation Sagitta.

Chart Coathanger Cluster, 
Brocchi's Cluster (Collinder 399)
Coathanger Cluster, Brocchi's Cluster (Collinder 399) in constellation Vulpecula. Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]

More Objects Nearby (±15°)

References

22«The Deep Sky Field Guide to Uranometria 2000.0» by Murray Cragin, James Lucik and Barry Rappaport; Willmann-Bell, Inc.; ISBN 0-943396-38-7
93Objekte der Saison: Cr 399 von Jürgen Lamprecht; Interstellarum3/95, S.48
147Aladin Lite; aladin.u-strasbg.fr/AladinLite (2020-12-23)
149SkySafari 6 Pro, Simulation Curriculum; skysafariastronomy.com
160The STScI Digitized Sky Survey; archive.stsci.edu/cgi-bin/dss_form
277«Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; klima-luft.de/steinicke (2021-02-17)