NGC 1817
Open cluster in the constellation Taurus
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NGC 1817 is an open cluster of stars in the constellation Taurus. It was discovered by English astronomer William Herschel in February 1784.[5] With an apparent magnitude of 7.7[3] and spanning 9.3 arc minutes across the sky, it is separated from the NGC 1807 cluster by just 26 arc minutes.[6][circular reference] Indeed, the two may actually be parts of a single extended cluster.[5]
| NGC 1817 | |
|---|---|
NGC 1817 as seen by the DSS | |
| Observation data (J2000 epoch) | |
| Right ascension | 05h 12m 15.(0)s[1] |
| Declination | +16° 41′ 2(4)″[1] |
| Distance | 6,430 ly (1,972 pc)[2] |
| Apparent magnitude (V) | 7.7[3] |
| Apparent dimensions (V) | 9.3′[3] |
| Physical characteristics | |
| Estimated age | 0.8−1.2[4] Gyr |
| Other designations | C 0509+166, Collinder 60 |
| Associations | |
| Constellation | Taurus |
The NGC 1817 cluster is around the same age as the Hyades, or perhaps a little younger at 0.8−1.2 billion years. The turnoff point for this cluster—where stars above a certain mass are evolving through the red giant stage—is twice the mass of the Sun.[7] The cluster is situated in the opposite side of the sky from the Galactic Center at a separation of 32 kly (9.9 kpc) from the core,[7] and is around 1.3 kly (0.4 kpc) away from the Galactic plane.[4]
Measurements of the proper motion of 810 stars within a 1.5° region centered on the cluster suggest that it has at least 169 members.[8] Of these, there is a total of 26 variable stars, including three candidate Gamma Doradus variable stars and sixteen Delta Scuti variables.[9] This unusually high proportion of Delta Scuti variables is likely the result of the turnoff point being located within the instability strip.[5]
Gallery
Open clusters NGC 1807 and 1817 showing separation of 26'
