This week we have a look at an object that got flagged up by one of our HOYS-LCO participants a year and a half ago, when the group started to investigate light curves in our database. It is the known young star 2MASS J21524274+4710132, situated in the Cocoon Nebula (IC5146). The object is a good example of how long term monitoring can change your view about a particular object.

When the object got first mentioned to us, we had about four years worth of data. The light curve looked like it was periodic with a period of roughly two years. We had observed the star to increase its brightness by about one magnitude over a year and a half, to then drop the brightness by one magnitude and do the same again. There were also some short term (weeks) one magnitude dimming events that randomly occurred, but nothing else to write home about.

Since then the behaviour has completely changed. In the first year, the brightness dropped by about two magnitudes, while the short term variations at least doubled in magnitude. In the last observing season the object was initially brighter again, but getting fainter. It has now started to vary by 3-4 magnitudes on reasonably short (month) timescales. We will see what happens next.

One interpretation of this change could be that there is an increase in material being moved into the inner disk, thus increasing the frequency and depth of the dimming events. Looking through our entire sample of light curves for this kind of behaviour can tell us how often such events happen, and how long they will last. This will allow us to draw conclusions about the structure and dynamics of the inner disk regions around these young stars – which is were ultimately terrestrial planets are forming.