Cluster NGC 6823 with Emission Nebula Sh 2-86

NGC 6823 + Sh 2-86
NGC 6823 + Sh 2-86: Open cluster NGC 6823 with emission nebula Sh 2-86; 500 mm Cassegrain 3625 mm f/7.2; SBIG STL11K; 240+3*40 min LRGB; Bernese Highlands; © 2015 Radek Chromik

History

The open star cluster NGC 6823 was discovered on July 17, 1785 by the German-British astronomer Wilhelm Herschel with his 18.7" reflecting telescope. [277] He described it as a «cluster, fairly rich in stars, oblong, stars 11th to 12th magnitude». [313] At that time he did not notice the emission nebula surrounding the star cluster.

On August 7, 1864, the German astronomer Albert Marth discovered the small emission nebula NGC 6820, which he described as «faint, small, round, brighter in the center». He was on the island of Malta at the time, observing the sky with William Lassell's 48 inch f/9.4 Newtonian telescope. [277, 313] Some mistakenly equate NGC 6820 with the emission nebula around star cluster NGC 6823, including Roger W. Sinnot in his NGC 2000.0 catalog revised in 1988. [142] However, the description and position given back then fit the small emission nebula about a quarter degree southwest of the center of the open star cluster.

The American astronomer Stewart Sharpless found the large emission nebula Sh 2-86 (LBN 059.38-00.15) around the open star cluster NGC 6823 while searching the photo plates of the «Palomar Observatory Sky Survey» made with the 48 inch Schmidt telescope. He published This discovery together with a total of 313 H-II regions in a catalog in 1959. He also incorrectly gave NGC 6820 as the nebula around the star cluster NGC 6823. [310]

NGC 6820
NGC 6820: Emission knots in nebula Sh2-86 and star cluster NGC 6823. Sections from different sky surveys [147]

Physical Properties

This object is a star-forming region. The distance of the star cluster NGC 6823 is given rather imprecisely with 1.7 kpc to 6.3 kpc (5500 to 20'000 light years). [145] He is probably closer to the end of this range. The star cluster features a central trapezoidal system BD+22°3782 with bright O- and B-type stars. About 92 stars brighter than 13 mag belong to the cluster, which is divided into an inner and outer area. The Hertzsprung–Russell (HR) diagram of both regions shows a well-defined upper main sequence with an estimated age of 2 million years. Another pre-main sequence population with an estimated age of 200'000 to 500'000 years in the outer region may have been produced by an earlier supernova explosion from one of the massive O stars at the center of NGC 6823. [400]

«Revised New General Catalogue and Index Catalogue», «Historically Corrected New General Catalogue», Dr. Wolfgang Steinicke, 2021 [277]
NameRADecTypeBmagVmagDimDreyer DescriptionIdentification
NGC 6820 19 42 28.0+23 05 15EN15.00.50 × 0.5F, S, R, bMIRAS 19403+2258, knot in Sh2-86
NGC 6823 19 43 10.0+23 18 00OCL (I3pn)7.17.00Cl, eRi, E, st 11…12OCL 124, LBN 135

Finder Chart

Open star cluster NGC 6823 is located in the constellation Vulpecula. The best observation time is May to October.

Chart NGC 6823
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]

References

142NGC 2000.0, The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J.L.E. Dreyer; edited by Roger W. Sinnott; Sky Publishing Corporation and Cambridge University Press (1988); cdsarc.unistra.fr/viz-bin/cat/VII/118 (2021-02-18)
145SIMBAD astronomical database; simbad.u-strasbg.fr/simbad
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)
310«A Catalogue of H II Regions» Stewart Sharpless, US Naval Observatory, 1959; DOI:10.1086/190049; Bibcode:1959ApJS....4..257S
313«A New General Catalogue of Nebulae and Clusters of Stars, being the Catalogue of the late Sir John F.W. Herschel, Bart., revised, corrected, and enlarged» Dreyer, J. L. E. (1888); Memoirs of the Royal Astronomical Society. 49: 1–237; Bibcode:1888MmRAS..49....1D
400«Young stellar objects in NGC 6823» B. Riaz, E. L. Martín, R. Tata, J.-L. Monin, N. Phan-Bao, H. Bouy; Monthly Notices of the Royal Astronomical Society, Volume 419, Issue 3, January 2012, Pages 1887–1912; DOI:10.1111/j.1365-2966.2011.19841.x