A survey for variable young stars with small telescopes: III – Warm spots on the active star V1598Cyg
Our new paper with the above title has been accepted for publication by Monthly Notices of the Royal Astronomical Society last week. We have analysed the HOYS data for the known variable star V1598Cyg, which is situated in the field of the Pelican Nebula. According to the distance measurement from Gaia, we find that the star itself is not a member of the star forming region, but rather a foreground object, about half way to the Pelican Nebula.
The star shows long term variations on a time scale of about six years, as well as short term variability with a period of 19 hours and 47.4 minutes. The latter is most likely caused by spots on the surface of the star. They rotate in and out of view and thus cause the brightness variations. Our long term HOYS data allows us to trace how the amplitude of the variability changes over time and at different wavelength. This in turn gives us the possibility to model the temperature and size of the spots on the surface and study their evolution.
We find that the spots are a few 100 degrees warmer than the surface of the star, rather than being colder like Sun spots. They also cover between 10 and 30% of the visible hemisphere of the star. Hence, the light curve variability is most likely caused by bright region in the chromosphere of the star, which sits above the photosphere. We also find that the spots typically last between six months and one year. However, it is still not clear if the object is a young fast rotating star, a close short period binary or possibly both.
If you are interested in reading the full paper, please click on this link.