After many weeks of looking at light curves of young stars, we return to one of the other types of variable objects found in the HOYS data – Giant Stars. We have a look at the Mira type variable KS Cyg. We did look at the star about one year ago, but it is always interesting to see if and how objects change over time.

In the above light curve we show the I -band and V-band data we have for the object. Note that we have shifted the V data by three magnitudes for better visibility. The period of approximately 300 days for the Mira-like pulsations are clearly visibly. Thus, the minima and maxima of the light curve shift by about two months from one year to the next. This allows us over time to fully sample the phased light curve.

The amplitude of the variations differs from filter to filter. While it is only about 2mag in the I-band, it increases to almost 4.5mag in the V filter. Thus, the object is not only changing brightness but also its colour. During the maximum the V-I colour is roughly 3.5mag, but this changes to almost 6mag. This means the object is very red and cold during the minima.