NGC 637
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| 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 |
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 light years from the Sun.[1] The cluster is small but compact, and is readily visible in a small telescope.[2]
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]
