NGC 6940

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NGC 6940
NGC 6940 AOFPK.jpg
Observation data (J2000 epoch)
Constellation Vulpecula
Right ascension 20h 34m 26s [1]
Declination +28° 17′ 00″ [1]
Distance 2,510 ly [2] (770 pc [2] )
Apparent magnitude (V)6.3 [1]
Apparent dimensions (V)25'
Physical characteristics
Estimated age720 millions years [2]
Other designationsMelotte 232
See also: Open cluster, List of open clusters
The location of NGC 6940 NGC 6940 map.png
The location of NGC 6940

NGC 6940 is an open cluster in the constellation Vulpecula. It was discovered by William Herschel in 1784. The cluster is nearly a billion years old and it is located 2,500 light years away. It is considered the finest open cluster in the constellation. [3]

Contents

Observation

It is located a bit more than two degrees south-southeast of 41 Cygni and three and a half degrees southwest from 52 Cygni. The cluster is bright enough to be seen even with small binoculars, which can partially resolve it. [3] NGC 6940 is included in the Herschel 400 Catalogue.

Characteristics

NGC 6940 has hundreds of members. The cluster is quite scattered and in between its members are also visible field stars. For example, two bright stars, an 8.6 mag B8III giant star at the NE edge and a 9.1 mag A0III giant at the SW corner of the cluster are too young to be true members of NGC 6940 and are probably background stars. The brightest star (lucida) of NGC 6940 is the red giant FG Vulpeculae, a semiregular variable star whose magnitude ranges from 9.0 to 9.5 every 80 days approximately. [3] NGC 6940 is rich in red giants, more than 20 according to WEBDA database. Based on the spectroscopic analysis of twelve of them, the cluster age was estimated to be 1.1 billion years, with a turn-off mass of 2 M⊙. Its metallicity is close to the one of the Sun. [4] In NGC 6940 have been detected 8 variable stars whose variability is consistent with the delta Scuti variables. [5]

A study of the cluster by ROSAT in soft X-rays revealed four sources that are identified as cluster members. [6] One more source was attributed to a possible cluster K0 giant star member, which was later confirmed to be a cluster member. [7] Three of these sources were identified as binary stars, from a total of six known to exist in the cluster. The luminosity of the sources was typical of RS Canum Venaticorum variables, close binaries that could retain very active coronal sources despite the age of the cluster. [6]

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<span class="mw-page-title-main">Cygnus (constellation)</span> Constellation in the northern celestial hemisphere

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<span class="mw-page-title-main">Jewel Box (star cluster)</span> Open cluster in the constellation Crux

The Jewel Box is an open cluster in the constellation Crux, originally discovered by Nicolas Louis de Lacaille in 1751–1752. This cluster was later named the Jewel Box by John Herschel when he described its telescopic appearance as "...a superb piece of fancy jewellery". It is easily visible to the naked eye as a hazy star some 1.0° southeast of the first-magnitude star Mimosa. This hazy star was given the Bayer star designation "Kappa Crucis", from which the cluster takes one of its common names. The modern designation Kappa Crucis has been assigned to one of the stars in the base of the A-shaped asterism of the cluster

<span class="mw-page-title-main">Messier 23</span> Open cluster in Sagittarius

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<span class="mw-page-title-main">Messier 39</span> Open cluster in the constellation Cygnus

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<span class="mw-page-title-main">NGC 663</span> Open star cluster in the constellation Cassiopeia

NGC 663 is a young open cluster in the constellation of Cassiopeia. It has an estimated 400 stars and spans about a quarter of a degree across the sky. It can reportedly be detected with the unaided eye, although a telescope is recommended for best viewing. The brightest members of the cluster can be viewed with binoculars. Although the listed visual magnitude is 7.1, several observers have reported higher estimates.

<span class="mw-page-title-main">NGC 6709</span> Open cluster in the constellation Aquila

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<span class="mw-page-title-main">NGC 6193</span> Open star cluster in the constellation Ara

NGC 6193 is open cluster containing 27 stars in the constellation Ara, visible to the unaided eye. NGC 6193 lies at the center of the Ara OB1 association, which extends over a square degree. The cluster is associated with neighboring regions of the nebulosity NGC 6188.

<span class="mw-page-title-main">NGC 6834</span> Open cluster in the constellation Cygnus

NGC 6834 is a young open cluster of stars located about 10,850 light years from the Sun in the constellation Cygnus. It was discovered on July 17, 1784 by Anglo-German astronomer William Herschel. The cluster has a visual magnitude of 7.8, which is dimmed by 2.1 magnitudes due to interstellar dust. Half the cluster members lie within an angular radius of 6′.

<span class="mw-page-title-main">NGC 654</span> Open star cluster in the constellation Cassiopeia

NGC 654 is an open cluster in the constellation Cassiopeia. It was discovered by William Herschel in 1787. With apparent magnitude 6.5, it can be observed by binoculars. It is located 2,5° northeast of the star Delta Cassiopeiae. In the same low power field can also be seen the open clusters NGC 663 and NGC 659. It surrounds a 7th magnitude yellowish star, an F5Ia supergiant, which is a possible member of the group.

<span class="mw-page-title-main">NGC 6939</span> Open cluster in the constellation Cepheus

NGC 6939 is an open cluster in the constellation Cepheus. It was discovered by William Herschel in 1798. The cluster lies 2/3° northwest from the spiral galaxy NGC 6946. The cluster lies approximately 4,000 light years away and it is over a billion years old.

<span class="mw-page-title-main">NGC 2539</span> Open cluster in the constellation Puppis

NGC 2539 is an open cluster in the constellation Puppis, located at the north edge of the constellation. It was discovered by William Herschel on January 31, 1785. It is a moderately rich cluster and with little central concentration, with Trumpler class II1m.

<span class="mw-page-title-main">NGC 2659</span> Open cluster in the constellation Vela

NGC 2659 is an open cluster in the constellation Vela. It was discovered by John Herschel on 3 February, 1835. It is of Trumpler class III3m. It is a young cluster, with age nearly 8 million years. The core of the cluster is 1.93 parsec across and the total radius is 3.6 pc. The total number of stars that belong to the cluster is estimated to be 1,801 ± 608 stars and the total mass 857 ± 237 M☉. Among its members, one is a Be star, with four more possible Be stars.

NGC 5662 is an open cluster in the constellation Centaurus. It was discovered by Nicolas Louis de Lacaille on May 17, 1752 from South Africa. James Dunlop observed it on July 10, 1826 from Parramatta, Australia and added it to his catalog as No. 342.

<span class="mw-page-title-main">NGC 4349</span> Open cluster in the constellation Crux

NGC 4349 is an open cluster in the constellation Crux. It was discovered by James Dunlop in 1826. It is located approximately 7,000 light years away from Earth.

<span class="mw-page-title-main">NGC 4103</span> Open cluster in the constellation Crux

NGC 4103 is an open cluster in the constellation Crux. It was discovered by James Dunlop in 1826. It is located approximately 5,000 light years away from Earth, in the Carina-Sagittarius arm.

NGC 4815 is an open cluster in the constellation Musca. It was discovered by John Herschel in 1834. It is located approximately 10,000 light years away from Earth.

<span class="mw-page-title-main">NGC 2527</span> Open cluster in the constellation Puppis

NGC 2527 is an open cluster in the constellation Puppis. It was discovered by William Herschel on December 9, 1784. The cluster was also observed by John Herschel on January 7, 1831. He also observed it on February 5, 1837, identifying it as a different object, which was catalogued as NGC 2520. It is a poor cluster and with no central concentration, with Trumpler class III1p.

<span class="mw-page-title-main">NGC 7160</span> Open cluster in the constellation Cepheus

NGC 7160 is an open cluster in the constellation Cepheus. It was discovered by William Herschel on November 9, 1789. The cluster was also observed by John Herschel on October 7, 1829. It is a poor cluster and with little central concentration, with Trumpler class II3p. It is part of the stellar association Cepheus OB2, located one degree south-southwest of VV Cephei.

<span class="mw-page-title-main">NGC 6910</span> Open cluster in the constellation Cygnus

NGC 6910 is an open cluster in the constellation Cygnus. It was discovered by William Herschel on October 17, 1786. The cluster was also observed by John Herschel on September 18, 1828. It is a poor cluster and with prominent central concentration, with Trumpler class I2p. NGC 6910 is the core cluster of the stellar association Cygnus OB9.

References

  1. 1 2 3 "NGC 6940". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 2017-06-19.
  2. 1 2 3 WEBDA: NGC 6940
  3. 1 2 3 Rhemann, Gerald; Crossen, Craig (2004). Sky Vistas Astronomy for Binoculars and Richest-Field Telescopes. Vienna: Springer Vienna. p. 64. ISBN   978-3709106266 . Retrieved 18 July 2017.
  4. ↑ Böcek Topcu, G.; Afşar, M.; Sneden, C. (21 November 2016). "The chemical compositions and evolutionary status of red giants in the open cluster NGC 6940". Monthly Notices of the Royal Astronomical Society. 463 (1): 580–597. arXiv: 1411.7608 . Bibcode:2016MNRAS.463..580B. doi:10.1093/mnras/stw1974. S2CID   119182329.
  5. ↑ Rose, Michael B.; Hintz, Eric G. (November 2007). "A Search for Low-Amplitude Variability in Six Open Clusters Using the Robust Median Statistic". The Astronomical Journal. 134 (5): 2067–2078. Bibcode:2007AJ....134.2067R. doi: 10.1086/522963 .
  6. 1 2 Belloni, T.; Tagliaferri, G. (October 1997). "Soft X-ray emission from intermediate-age open clusters: NGC 6940". Astronomy and Astrophysics. 326: 608–613. Bibcode:1997A&A...326..608B . Retrieved 18 July 2017.
  7. ↑ van den Berg, M.; Verbunt, F. (15 August 2001). "An optical study of X-ray sources in the old open clusters NGC 752 and NGC 6940". Astronomy & Astrophysics. 375 (2): 387–396. Bibcode:2001A&A...375..387V. doi: 10.1051/0004-6361:20010767 . Retrieved 18 July 2017.

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