NGC 654 explained

NGC 654
Credit:Antonio F. Sánchez
Type:Open Cluster
Epoch:J2000
Constellation:Cassiopeia
Ra:[1]
Dist Ly:7,830 ly
Dist Pc:2,400 pc
Appmag V:6.5
Size V:5'
Age:14 million years[2]
Names:Cr 18

NGC 654 is an open cluster in the constellation Cassiopeia. It was discovered by William Herschel in 1787. With apparent magnitude 6.5, it can be observed by binoculars.[3] It is located 2,5° northeast of the star Delta Cassiopeiae. In the same low power field can also be seen the open clusters NGC 663 and NGC 659. It surrounds a 7th magnitude yellowish star, an F5Ia supergiant, which is a possible member of the group.[4]

It is 2,400 parsec away. It is a very young cluster, aged approximately 15 million years, but it could be as old as 40 million years, with a time spread of star formation of at least ~20 Myr. The central region of the cluster shows less reddening than the rest of the cluster.[5] One explanation is that between the Solar System and the cluster lie two dust layers, one at 200pc and one more at 1Kpc.[6] Behind the cluster is one more dust layer. The cluster has approx. 80 members, including three Be stars and a few luminous stars like HD 10494 and F5Ia. The earliest spectral type is around B0.[7]

NGC 654 is assumed to form part of the stellar association Cassiopeia OB8, that is located in the Perseus arm of the Milky Way, along with the open clusters M103, NGC 663, NGC 659, and some supergiant stars scattered between them, all of them having similar ages and distances.[8] [9]

Notes and References

  1. NGC 654. 2015-06-19.
  2. https://www.univie.ac.at/webda/cgi-bin/ocl_page.cgi?dirname=ngc0654 WEBDA: NGC 654
  3. Book: Stephen James O'Meara. Deep-Sky Companions: The Secret Deep vol. 4. 2011. Cambridge University Press. 978-1-139-50007-4. 31–33. O'Meara.
  4. Huestamendia, G. . del Rio, G. . Mermilliod, J.-C. . UBV photometry of open clusters in the Cassiopeia region. II - Photoelectric observations of NGC 654. Astronomy and Astrophysics Supplement Series. July 1993. 100. 1. 25–32. 29 December 2015. 1993A&AS..100...25H .
  5. A. K. Pandey . K. Upadhyay . K. Ogura . Ram Sagar . V. Mohan . H. Mito . H. C. Bhatt . B. C. Bhatt . Stellar contents of two young open clusters: NGC 663 and 654. MNRAS. April 2005. 358. 4. 1290–1308. 10.1111/j.1365-2966.2005.08784.x. 2005MNRAS.358.1290P . free .
  6. Biman J. Medhi . Maheswar G. . J. C. Pandey . T. S. Kumar . Ram Sagar . Optical polarimetric study of open clusters: distribution of interstellar matter towards NGC 654. MNRAS. 2008. 388. 1. 105–116. 10.1111/j.1365-2966.2008.13405.x. 29 December 2015. 0804.4739 . 2008MNRAS.388..105M . 119297788 .
  7. H.M. Shi - J.Y. Hu. Spectroscopic observations of young open clusters: IC 1805, NGC 654 and NGC 6823. Astron. Astrophys. Suppl. Ser.. April 1999. 136. 2. 313–331. 10.1051/aas:1999217. 29 December 2015. 1999A&AS..136..313S . free.
  8. Negueruela, I. . González-Fernández, C. . Marco, A. . Clark, J. S. . A massive association around the obscured open cluster RSGC3 . Astronomy & Astrophysics . 528 . A59 . 2011 . 10.1051/0004-6361/201016102 . 2011A&A...528A..59N. 1102.0028 . 53517711 .
  9. Humphreys, R. M. . Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way. . Astrophysical Journal Supplement Series . 38 . 309–350 . 1978 . 10.1086/190559 . 1978ApJS...38..309H.