Variable stars in the field of intermediate-age open cluster NGC 559

Abstract

This work presents the first long-term photometric variability survey of the intermediate-age open cluster NGC 559. Time-series V band photometric observations on 40 nights taken over more than three years with three different telescopes are analyzed to search for variable stars in the cluster. We investigate the data for the periodicity analysis and reveal 70 variable stars including 67 periodic variables in the target field, all of them are newly discovered. The membership analysis of the periodic variables reveal that 30 of them belong to the cluster and remaining 37 are identified as field variables. Out of the 67 periodic variables, 48 are short-period (P < 1 day) variables and 19 are long-period (P > 1 day) variables. The variable stars have periodicity between 3 hours to 41 days and their brightness ranges from V = 10.9 to 19.3 mag. The periodic variables belonging to the cluster are then classified into different variability types on the basis of observational properties such as shape of the light curves, periods, amplitudes, as well as their positions in the Hertzsprung-Russell (H-R) diagram. As a result, we identify one Algol type eclipsing binary, one possible blue straggler star, 3 slowly pulsating B type stars, 5 rotational variables, 11 non-pulsating variables, 2 FKCOM variables and remaining 7 are characterized as miscellaneous variables. We also identify three Eclipsing Binary stars (EBs) belonging to the field star population. The PHOEBE package is used to analyse the light curve of all four EBs in order to determine the parameters of the binary systems such as masses, temperatures and radii.

Investigating Stellar Variability in the Open Cluster Region NGC 381

“…We examined the light curves of all the periodic variables for the presence of primary and secondary minima, which is the signature of binary systems, by plotting phase-folded light curves corresponding to twice the obtained periods. The amplitude of the variation in periodic variables was calculated by taking half of the difference in the mean magnitudes of the three faintest and the three brightest points in the curves (Joshi et al 2020a). We have provided the basic parameters such as period, amplitude, and magnitude in Table 2.…”

“…Mowlavi et al (2016) classified these stars as fast-rotating pulsating B (FaRPB) variable stars based on a spectroscopic study that revealed that the majority of these stars were fast-rotating. FaRPB stars are known to have short periods (p < 0.55 days; Mowlavi et al 2016;Joshi et al 2020a). However, these variables were classified as miscellaneous variables since they have periods significantly longer than 0.55 days.…”

“…= +61:35:18.24). This is the very first variability study of cluster NGC 381 and is part of our ongoing project to investigate the variability of poorly studied open clusters (Joshi et al 2020a). In our previous study, we found a total of 132 member stars of the cluster after applying a 50% probability cutoff in this region.…”

“…Open clusters are known to host a rich variety of variable stars (Xue et al 2019;Joshi et al 2020a;Sandquist et al 2020). These stars play a crucial role in our understanding of stars' intrinsic properties such as pulsation, rotation, and emission.…”

Searching for Variable Stars in the Open Cluster NGC 2355 and Its Surrounding Region

“…Open clusters are exceptional laboratories for us to understand the fundamental astrophysical processes and one of the principal components of the galaxy. It is believed that a significant number of stars in the galaxy are formed in clusters (Joshi et al 2020). Therefore, their extensive study is vital to infer the star formation history in the galaxy (Phelps & Janes 1994) and to probe the Galactic structure (Chen et al 2003;Cantat-Gaudin et al 2018).…”