NGC 637

NGC 637 is an open cluster of stars in the northern constellation of Cassiopeia, positioned about 1.5° to the WNW of the star Epsilon Cassiopeiae.^[2][5] The cluster was discovered on 9 November 1787 by German-born English astronomer William Herschel.^[6] It is located in the Perseus Arm of the Milky Way,^[7] at a distance of approximately 7.045 kilolight-years from the Sun.^[1] The cluster is small but compact, and is readily visible in a small telescope.^[2]

NGC 637
Observation data (J2000.0 epoch)
Right ascension	01h 43m 04.0s[1]
Declination	+64° 02′ 24″[1]
Distance	7.045 ± 1.409 kly (2.160 ± 0.432 kpc)[1]
Apparent magnitude (V)	8.2[2]
Apparent dimensions (V)	4.2′[3]
Physical characteristics
Estimated age	10 ± 5 Myr[3]
Other designations	Cr 17, NGC 637[4]
Associations
Constellation	Cassiopeia
See also: Open cluster, List of open clusters

This is a young cluster with an estimated age of 5–15 million years.^[3] It has a Trumpler class of I2m, indicating it is strongly concentrated (I) with an intermediate range of brightness variation (2) and a moderate richness of stars (m).^[7] The cluster has 55^[2] members and an angular radius of 4′.2, corresponding to a physical radius of 9.8 ly (3.0 pc).^[7] It has a core radius of 0.36′±0.13′.^[8]

The seven brightest members are all over 10th magnitude, with five known to be variable. A total of four β Cephei-type variables have been identified, one of the highest such totals for an open cluster.^[9] A classical Be star candidate has been detected.^[7] The distribution of the cluster's stars on the Hertzsprung–Russell diagram shows a noticeable gap on the main sequence, which is not explained by missing data.^[8]

References

1. Wu, Zhen-Yu; et al. (November 2009). "The orbits of open clusters in the Galaxy". Monthly Notices of the Royal Astronomical Society. 399 (4): 2146–2164. arXiv:0909.3737. Bibcode:2009MNRAS.399.2146W. doi:10.1111/j.1365-2966.2009.15416.x. S2CID 6066790.
2. O'Meara, Steve (June 14, 2007). Herschel 400 Observing Guide. Cambridge University Press. p. 296. ISBN 9780521858939.
3. Yadav, R. K. S.; Kumar, Brijesh; Subramaniam, A.; Sagar, Ram; et al. (November 2008). "Optical and near-infrared photometric study of the open cluster NGC 637 and 957". Monthly Notices of the Royal Astronomical Society. 390 (3): 985–996. arXiv:0810.1409. Bibcode:2008MNRAS.390..985Y. doi:10.1111/j.1365-2966.2008.13740.x. S2CID 18096918.
4. "NGC 637". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-02-29.
5. Sinnott, Roger W.; Perryman, Michael A. C. (1997). Millennium Star Atlas. Vol. 1. Sky Publishing Corporation and the European Space Agency. p. 34. ISBN 0-933346-84-0.
6. "New General Catalog Objects: NGC 600 - 649". cseligman.com. Retrieved 2018-01-05.
7. Kharchenko, N. V.; et al. (August 2005). "Astrophysical parameters of Galactic open clusters". Astronomy and Astrophysics. 438 (3): 1163–1173. arXiv:astro-ph/0501674. Bibcode:2005A&A...438.1163K. doi:10.1051/0004-6361:20042523. S2CID 9079873.
8. Hasan, Priya; et al. (November 2008). "The structure and dynamics of young star clusters: King 16, NGC 1931, NGC 637 and NGC 189". Astrophysics and Space Science. 318 (1–2): 25–33. arXiv:0808.1785. Bibcode:2008Ap&SS.318...25H. doi:10.1007/s10509-008-9888-2. S2CID 18982625.
9. Handler, G.; Meingast, S. (September 2011). "New β Cephei stars in the young open cluster NGC 637". Astronomy & Astrophysics. 533: 6. arXiv:1105.3121. Bibcode:2011A&A...533A..70H. doi:10.1051/0004-6361/201116874. S2CID 55061600. A70.

External links

• NGC 637 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
• SEDS