Chinese astronomers have conducted a photometric survey of ancient scattered cluster NGC 188 using the Nanshan One-Meter Wide Field Telescope (NOWT). As a result, they identified many variable stars, one of which was discovered for the first time. The discovery was reported on April 25 at the preprocessing warehouse. arXiv.

Detection and study of variable stars can provide important clues about stellar structure and evolution. Investigating variables can also be useful for better understanding the scale of the universe’s distance.

NGC 188 (also known as Caldwell 1) is located about 5,400 light-years away in the constellation Cepheus and is a well-studied diffuse galactic cluster (OC) estimated to be about 6.8 billion years old. It is one of the oldest, richest OCs in the Milky Way galaxy and is known to contain dozens of variable stars.

A research team led by Fan-Fang Song of the Xinjiang Astronomical Observatory in China conducted another study of NGC 188, identifying 25 variable stars, one of which is new. They used NOWT to perform a charge-coupled device (CCD) photometric study of this cluster.

“In this paper, we present a photometric investigation of the scattered cluster NGC 188 in the V-band time series, with a particular focus on the variables,” the researchers write.

In total, the survey revealed 25 variable stars in a 55×45 arc-minute field of view. ² (corresponding to 2900 × 2400 pixels) NGC 188 is around. Variables are labeled V1 to V25 and the results show that 16 variables are members of the cluster and the remaining stars belong to the field star population.

The newly discovered star, designated V18, is a periodic variable with a period of about 0.317 days. The results show that it is a field star about 6,000 light-years away with an effective temperature of 6,116 K.

According to the authors of the paper, the data collected indicates that V18 is most likely a W Ursae Majoris, W UMa (EW) system. In general, EWs are faint binary variable stars – close binary systems of spectral types F, G, or K that share a shell of material and are in contact with each other. In addition to V18, there are 11 other EWs in 25 variable samples defined from V1 to V11.

The data obtained by Song’s team also allowed them to reclassify a previously known variant, V21 (also known as V0769 Pocket). NOWT observations suggest that V21 could possibly be an EA-type shaded binary system, as a 0.5 magnitude dimming was detected in the light curve rather than a BY Draconis-type variant as suggested in previous studies.