NGC 1817

NGC 1817
NGC 1817 as seen by the DSS
Observation data (J2000 epoch)
Right ascension05h 12m 15.(0)s[1]
Declination+16° 41′ 2(4)″[1]
Distance6,430 ly (1,972 pc)[2]
Apparent magnitude (V)7.7[3]
Apparent dimensions (V)9.3′[3]
Physical characteristics
Estimated age0.8−1.2[4] Gyr
Other designationsC 0509+166, Collinder 60
Associations
ConstellationTaurus
See also: Open cluster, List of open clusters

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]

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]

  1. ^ a b Cite error: The named reference MNRAS399_4_2146 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference aaa438_3_1163 was invoked but never defined (see the help page).
  3. ^ a b c Cite error: The named reference theskylive was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference mnras437_2_1241 was invoked but never defined (see the help page).
  5. ^ a b c Cite error: The named reference omeara2011 was invoked but never defined (see the help page).
  6. ^ "NGC 1807 and 1817 separation". Retrieved 11 December 2021.
  7. ^ a b Cite error: The named reference mnras419_2_1350 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference aa426_819 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference ca160_9 was invoked but never defined (see the help page).