Chinese astronomers used the Nanshan One-meter Wide-field Telescope (NOWT) to search for variable stars in the open cluster NGC 2355 and its surrounding field. In this region, they discovered 72 new variables. The discovery is detailed in a paper published on arXiv.org on June 14th.
Because star clusters are collections of stars with similar properties, such as age, distance, and initial composition, they provide excellent opportunities to study stellar evolution. Astronomers frequently look for variable stars in young clusters, which could help them better understand pre-main-sequence (PMS) stars and thus the early stages of stellar evolution.
A team of astronomers led by Hong Wang of Xinjiang Astronomical Observatory in Xinjiang, China, recently used NOWT’s CCD camera to conduct an extensive search for variable stars in NGC 2355. NGC 2355 is a 5,400 light-year-distance open cluster in the constellation Gemini that is estimated to be 900 million years old. Only a few searches for variables in this cluster have been conducted so far.
“Based on time-series photometric observation data, we investigated the variable stars in the field surrounding NGC 2355. Over the course of 13 nights, the Nanshan One-meter Wide-field Telescope captured over 3,000 CCD frames in the V band “The researchers wrote about it in their paper.
Wang’s team discovered 88 variable stars in 13 nights of photometric observations. It was discovered that 72 of the 88 stars are new variables, while the rest are known variables from previous observations.
Based on the light curves of the stars in the sample, the researchers classified them into different types and derived fundamental parameters. Finally, 52 of the stars described in the paper are pulsating stars, 26 are eclipsing binaries, and four are rotating variables. The remaining six stars are variable stars of unknown type.
“We may need more observations later to identify and classify these unknown variable stars for those variable stars for which no type has been determined,” the astronomers wrote.
The 52 pulsating stars were further classified as Delta Scuti variables, RR Lyraes variables, Gamma Doradus variables, and Cepheid I variable stars. Eleven of the 26 eclipsing binaries are of the EW type, nine are of the EA type, and the rest are of the EB type.
In addition to the 11 previously known variables classified as cluster members by a study conducted in 2018, the researchers noted that four variable stars reported in the paper are members of NGC 2355. They are located in the cluster’s outer region and exhibit spatial and kinematic homogeneity with the cluster members. Furthermore, the authors discovered that NGC 2355 has a metallicity of about -0.07 dex and a reddening of 0.24.