NGC 129

NGC 129 is an open cluster in the constellation Cassiopeia. It was discovered by William Herschel in 1788. It is located almost exactly halfway between the bright stars Caph (β Cassiopeiae) and γ Cassiopeiae. It is large but not dense and can be observed by binoculars, through which the most obvious component is a small triangle of stars of magnitude 8 and 9, located in the center of the cluster.

NGC 129
DSS image of NGC 129
Observation data (J2000 epoch)
Right ascension00h 30m 00s[1]
Declination+60° 13′ 06″[1]
Distance5,450 ly (1,670 pc[2])
Apparent magnitude (V)6.5 [1]
Apparent dimensions (V)21'
Physical characteristics
Estimated age76 millions years[2]
Other designationsCollinder 2
Associations
ConstellationCassiopeia

NGC 129 contains several giant stars. The brightest member of the cluster is DL Cassiopeiae, a binary system which contains a Cepheid variable with a 8,00 day period. Using the fluctuations of the brightness of DL Cassiopeia from 8,7 to 9,28, Gieren et al. in 1994 determined the distance of NGC 129 to be 2034 ±110 pc (6.630 ±360 ly), much larger than the distance obtained by Turner et al. (1992), who obtained a distance of 1,670 ±13 pc from ZAMS fitting of the cluster. A possible cause of this difference is the different level of obstruction of light and star reddening of the stars of the cluster.[3] One more cepheid variable, V379 Cas, is also a possible member of NGC 129.[4]

References
  1. "NGC 129". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2015-06-19.
  2. Turner, David G.; Forbes, Douglas; Pedreros, Mario (September 1992). "Galactic clusters with associated Cepheid variables. II - NGC 129 and DL Cassiopeiae". Astronomical Journal. 104 (3): 1132–1143. Bibcode:1992AJ....104.1132T. doi:10.1086/116302.
  3. Gieren, W. P.; Welch, D. L.; Mermilliod, J.-C.; Matthews, J. M. & Hertling, G. (June 1994). "Independent distance determinations to Milky Way Cepheids in open clusters and associations. 1: The binary Cepheid DL CAS in NGC 129". The Astronomical Journal. 107 (6): 2093–2100. Bibcode:1994AJ....107.2093G. doi:10.1086/117019.
  4. Richard I. Anderson; Laurent Eyer & Nami Mowlavi (25 June 2013). "Cepheids in Open Clusters: An 8-D All-sky Census". Monthly Notices of the Royal Astronomical Society. 434 (3): 2238–2261. arXiv:1212.5119. Bibcode:2013MNRAS.434.2238A. doi:10.1093/mnras/stt1160.
  • Media related to NGC 129 at Wikimedia Commons
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