IC 4756

Open cluster in the constellation Serpens

IC 4756

Observation data (J2000 epoch)
Right ascension	18^h 38^m 31.2^s^[1]
Declination	+05° 29′ 24″^[1]
Distance	1.3 kly (400 pc)
Apparent magnitude (V)	4.6^[1]
Physical characteristics
Other designations	Cr 386, Mel 210
Associations
Constellation	Serpens
See also: Open cluster, List of open clusters

IC 4756 is a large bright open cluster in the constellation Serpens. Known as Graff's Cluster, it is bright enough to be seen with the naked eye and considered a fine cluster for binoculars or small telescopes.^[2]

IC 4756 is also known as the Tweedledee Cluster (paired with NGC 6633 as Tweedledum), also as the Secret Garden Cluster.^[3]

Metallicity of IC 4756 is similar to the Sun, at -0.02±0.01 dex.^[4]

Stars

There are some noteworthy stars in the cluster. HD 172365^[5] is a likely post-blue straggler in the IC 4756 that contains a large excess of lithium.^[6] HD 172189, also in IC 4756, is an Algol variable eclipsing binary^[7] with a 5.70 day period. The primary star in the system is also a Delta Scuti variable, undergoing multiple pulsation frequencies, which, combined with the eclipses, causes the system to vary by around a tenth of a magnitude.^[8]

References

^ ^a ^b ^c "IC 4756". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 30 November 2016.
^ Michael Bakich. "The Omega Nebula, Graff's Cluster, and planetary nebula IC 1295". astronomy.com. Retrieved 2020-10-05.
^ O'Meara, Stephen James (2007). Deep-Sky Companions: Hidden Treasures. Cambridge University Press. p. 457-458. ISBN 978-0521-83704-0.
^ Bagdonas, Vilius; Drazdauskas, Arnas; Tautvaišienė, Gražina; Smiljanic, Rodolfo; Chorniy, Yuriy (2018), "Chemical composition of giant stars in the open cluster IC 4756", Astronomy & Astrophysics, 615: A165, arXiv:1804.01975, Bibcode:2018A&A...615A.165B, doi:10.1051/0004-6361/201832695, S2CID 118857628
^ "HR 7008 – Star in Cluster". SIMBAD. Retrieved 14 December 2014.
^ Andrievsky, S. M.; Gorlova, N. I.; Klochkova, V. G.; Kovtyuch, V. V.; Panchuk, V. E. (1999). "The Lithium-rich supergiant HD172365". Astronomische Nachrichten. 320 (1): 35–41. Bibcode:1999AN....320...35A. doi:10.1002/1521-3994(199903)320:1<35::aid-asna35>3.0.co;2-f.
^ Ibanoǧlu, C.; Evren, S.; Taş, G.; Çakırlı, Ö.; Bozkurt, Z.; Afşar, M.; Sipahi, E.; Dal, H. A.; Özdarcan, O.; Çamurdan, D. Z.; Çamurdan, M.; Frasca, A. (2009). "Spectroscopic and photometric observations of the selected Algol-type binaries - IV. V799 Cassiopeiae, BX Piscium and HD 172189". Monthly Notices of the Royal Astronomical Society. 392 (2): 757. Bibcode:2009MNRAS.392..757I. doi:10.1111/j.1365-2966.2008.14087.x.
^ Costa, J. E. S.; Michel, E.; Peña, J.; Creevey, O.; Li, Z. P.; Chevreton, M.; Belmonte, J. A.; Alvarez, M.; Fox Machado, L.; Parrao, L.; Pérez Hernéndez, F.; Fernández, A.; Fremy, J. R.; Pau, S.; Alonso, R. (2007). "Pulsational frequencies of the eclipsing δ Scuti star HD 172189. Results of the STEPHI XIII campaign". Astronomy and Astrophysics. 468 (2): 637–642. arXiv:0706.4083. Bibcode:2007A&A...468..637C. doi:10.1051/0004-6361:20065784.

External links

Media related to IC 4756 at Wikimedia Commons
IC 4756 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

Constellation of Serpens

Stars

Bayer	α (Unukalhai) β (Chow) γ (Ainalhai) δ ε ζ η θ (Alya) ι κ (Gudja) λ μ ν ξ ο π ρ σ τ¹ τ² τ³ τ⁴ τ⁵ τ⁶ τ⁷ τ⁸ υ φ χ ψ ω
Flamsteed	3 4 5 6 7 8 10 11 (A¹) 14 16 25 (A²) 29 36 (b) 39 40 43 45 46 47 59 (d) 60 (c) 61 64 3 Her 47 Oph
Variable	R W X RT UZ VV VY WX AA AN AO AP AR AU BQ CT CV CW EG FH FI FK FL FQ FR LV LW LX MR MS MT MV MY NN NO NQ NW OO OU PS QV QX QY V382 V411
HR	5665 5690 5692 5706 5711 5740 5745 5783 5796 5831 5850 5859 5861 5874 5909 5913 5931 5992 6005 6011 6014 6016 6449 6496 6544 6562 6568 6600 6620 6666 6681 6755 6756 6757 6785 6830 6840 6843 6858 6890 6898 6928 6993 (e) 6999 7008 7048 7076 7144
HD	135061 135615 136027 136118 138085 142245 143436 145936 146740 157969 168112 168443 168746 (Alasia) 175541 (Kaveh)
Other	ADS 9544 AS 296 9 11 22 23 27 Gliese 701 Gliese 710 GJ 1224 GX 17+2 IRAS 18418-0440 MWC 297 MWC 922 PG 1510+234 PG 1605+072 PSR B1534+11 PSR J1719−1438 Ross 508 Serpens FIRS 1 Serpens SVS 20 Serpens X-1 W40 IRS 1A South

Exoplanets	CoRoT-9b CoRoT-11b CoRoT-22b CoRoT-23b CoRoT-27b HD 168746 b (Onasilos) HD 175541 b (Kavian) ω Serpentis b

Star
clusters

NGC	NGC 6535 NGC 6539 NGC 6604 NGC 6605
Other	IC 4756 Messier 5 Messier 16 Serpens OB2 Serpens South Palomar 5

Nebulae

Other	Abell 41 Eagle Nebula L134 L183 L483 Serpens cloud Sh2-54 Westerhout 40 Red Square Nebula S68

Galaxies

NGC	5887 5910 5911 5913 5919 5920 5921 5926 5928 5931 5936 5937 5940 5942 5941 5944 5951 5953 5954 5952 5956 5955 5957 5960 5962 5964 5970 5972 5975 5977 5980 5983 5984 5988 5991 5990 5994 5996 5997 6003 6004 6008 6006 6007 6009 6012 6010 6014 6020 6017 6018 6021 6022 6023 6027 6027a 6027b 6027c 6027d 6027e 6029 6033 6037 6036 6051 6063 6065 6066 6070 6080 6100 6118 6172
Other	317 318 321 323.1 324 326 Arp 72 Arp 220 4C 11.50 CGCG 049-033 Hoag's Object IC 4537 IC 4588 IRAS 15107+0724 NRAO 530 PDS 456 PG 1553+113 PGC 54493 PKS 1546+027

NGC