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