NGC 663

NGC 663
NGC 663 in Cassiopeia
Observation data (J2000 epoch)
Right ascension	01h 46.0m
Declination	+61° 15′
Distance	6,850 ly (2,100 pc)
Apparent magnitude (V)	7.1
Apparent dimensions (V)	16.0″
Physical characteristics
Other designations	Caldwell 10
See also: Open cluster, List of open clusters

NGC 663, also known as Caldwell 10, is young open cluster of about 400 stars in the Cassiopeia constellation. 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.^[1]

After adjusting for reddening due to interstellar dust, the distance modulus is estimated as 11.6 magnitudes. It is located about 2,100 parsecs distant with an estimated age of 20–25 million years.^[2] This means that stars of spectral class B2 or higher (in the sense of higher mass), are reaching the end of their main sequence lifespan.^[3] This cluster appears to be located in front of a molecular cloud, although the two are not physically associated. This cloud has the effect of blocking background stars from the visual image of the cluster as it lies at a distance of 300 parsecs.^[4]

This cluster is of interest because of the high number of Be stars, with a total of about 24 discovered. These are spectral class B stars that show prominent emission lines of hydrogen in their spectrum. Most of the Be stars in the cluster lie between spectral class B0 and B3.^[2] A candidate member of the cluster, LS I +61° 235, is a Be star with an X-ray binary component that has a period of about three years.^[5] There are at least five blue stragglers in the cluster. These are stars that formed by the merger of two other stars.^[3] Two of the cluster's star systems are likely eclipsing binaries with periods of 0.6 and 1.03 days.^[6]

References

1. ^ O'Meara, Stephen James (2002). The Caldwell objects, Deep-sky companions. Cambridge University Press. pp. 50–51. ISBN 0521827965. 
2. ^ ^{a b} Pigulski, A.; Kopacki, G.; Kolaczkowski, Z. (2001). "The young open cluster NGC 663 and its Be stars". Astronomy & Astrophysics 376 (1): 144–153. Bibcode 2001A&A...376..144P. doi:10.1051/0004-6361:20010974. 
3. ^ ^{a b} Marco, A.; Negueruela, I.; Motch, C. (August 29-September 2, 2005). "Proceedings of the conference - Blue Stragglers, Be Stars and X-ray Binaries in Open Clusters". Active OB-Stars: Laboratories for Stellare and Circumstellar Physics. Hokkai-Gakuen University, Sapporo, Japan. Bibcode 2007ASPC..361..388M. http://adsabs.harvard.edu/abs/2007ASPC..361..388M. Retrieved 2009-08-31. 
4. ^ Phelps, Randy L.; Janes, Kenneth A. (November 1993). "Young open clusters as probes of the star-formation process. 2: Mass and luminosity functions of young open clusters". Astronomical Journal 106 (5): 1870–1884. Bibcode 1993AJ....106.1870P. doi:10.1086/116772. 
5. ^ Reig, P.; Fabregat, J.; Coe, M. J.; Roche, P.; Chakrabarty, D.; Negueruela, I.; Steele, I. (June 1997). "The Be/X-ray binary LS I +61 235/RX J0146.9+6121: physical parameters and V/R variability". Astronomy and Astrophysics 322: 183–192. Bibcode 1997A&A...322..183R. 
6. ^ Pietrzynski, G. (July 1996). "Variable Stars in the Young Open Cluster NGC 663". Acta Astronomica 46: 357–360. Bibcode 1996AcA....46..357P. 

External links

• NGC 663 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

Coordinates: 01^h 46^m 16^s, +61° 13′ 06″