This week we look at the light curve of the variable star V1598Cyg in the Pelican Nebula (IC5070). On the phase of it (see plot) it seems to be rather boring with not much going on. But this could not be more wrong 🙂 Our light curve now has six years worth of data. As the source is least visible at about February each year, the parts of the light curve with very few observations roughly separate the years. Thus, the last group represents 2021 and the very first group 2016. We published a paper about the object last year, which included HOYS data until 2019. In that paper we include some other archival data and show that the star shows long term brightness changes with a period of about six years. This can now also be seen in the HOYS data alone, and the star has been at maximum brightness during the last year.
Besides the long term variations of about 0.1mag (or 10% in brightness), the data looks just like noise. However, as analysed in detail in the above mentioned paper, most of that variation is real. Indeed the star shows periodic variations in brightness with a period of 0.8246 days. As the period is shorter than the typical gap between the data points, it looks like noise. We find that the amplitude of the periodic variations is almost of the order of the long term trend. The periodic variability amplitude changes between 3 and 8% of the flux over time.
Despite our analysis, the true nature of the source is not yet fully clear. It could be a fast rotating young star or an older, close binary system, or a combination of the two. A detailed analysis has shown that the brightness variation are caused by a warm surface spot (or group of spots). The changes in amplitude over time allow us to trace how the spot(s) evolve their temperature and size. We are in the process to analyse similar light curves to study how spots on young stars evolve over time. This will allow us to study the structure of their inner accretion disks and magnetic fields.