Caldwell16 aka NGC 7243 Open Star cluster in the Constellation Lacerta

 

The open Star Cluster NGC 7243 captured at the JPO. Image Credit: Kurt Thrust using the Seestar S30 in EQ Mode with Infrared Filter. Cropped and enlarged.

Seestar S30 uncropped full field of vision version. Image Credit: Kurt Thrust.

" NGC 7243 is not imaged and posted that often by astro-imagers, which is a shame as the cluster is quite beautiful with its mix of red and blue stars". - Joel Cairo CEO of the JPO, the UK's most easterly astronomical observatory.

"The astronomical object shown above is NGC 7243 (also catalogued as Caldwell 16 and Collinder 448), an open star cluster located in the northern constellation of Lacerta. Situated approximately 2,800 light-years from Earth within the Galactic plane, the cluster presents an integrated apparent visual magnitude of approximately 6.4$ and spans an angular diameter of roughly 21 to 31 arcminutes.

Morphological and Dynamical Characteristics

• Trumpler Classification: NGC 7243 is classified as a Trumpler II 2m open cluster, indicating a moderately detached concentration with a medium range of stellar brightness and a moderate richness of member stars.

• Spatial Distribution: The cluster exhibits a loose, asymmetric, and elongated structure with distinct groupings. It is divided into sub-concentrations separated by a subtle, low-density dust lane. The core population lacks a central density spike, merging gradually into the surrounding background stellar field of the Milky Way disk.

• Mass and Membership: Photometric and proper motion analyses identify roughly 200 candidate member stars down to magnitude 15.5, with total estimated cluster mass ranging between 348 solar M and 522 solar M.

Stellar Population and Evolutionary Status

• Cluster Age: Isochrone fitting to the main sequence turnoff indicates an age of 250 million years.

• Spectral Characteristics: The brightest main-sequence members are late B-type stars (earliest spectral type B5 III). The presence of blue-white stars along the upper main sequence, alongside evolving stars transitioning toward the red giant branch, produces a distinct color contrast against the field stars.

• Extinction & Environment: Because NGC 7243 resides within the Galactic disk, the field is characterized by modest interstellar extinction, visible as subtle background interstellar dust patches interspersed among the field stars". - Gary Gemini Coms Manager at the Jodrell Plank Observatory.