NGC 637

NGC 637
NGC 637 DSS
Observation data (J2000.0 epoch)
Right ascension01h 43m 04.0s[1]
Declination+64° 02′ 24″[1]
Distance7.045 ± 1.409 kly (2.160 ± 0.432 kpc)[1]
Apparent magnitude (V)8.2[2]
Apparent dimensions (V)4.2′[3]
Physical characteristics
Estimated age10 ± 5 Myr[3]
Other designationsCr 17, NGC 637[4]
Associations
ConstellationCassiopeia
See also: Open cluster, List of open clusters

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]

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]

  1. ^ a b c d Cite error: The named reference Wu2009 was invoked but never defined (see the help page).
  2. ^ a b c d Cite error: The named reference OMeara296 was invoked but never defined (see the help page).
  3. ^ a b c Cite error: The named reference mnras390_3_985 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference Sinnott1997 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference cseligman was invoked but never defined (see the help page).
  7. ^ a b c d Cite error: The named reference aaa438_3_1163 was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference Hasan2008 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Handler2011 was invoked but never defined (see the help page).