Happy Christmas everyone!

This weeks light curve is of the the star GP Mon in the Christmas Tree Cluster NGC2264. It is a know variable star of Orion Type at a Gaia distance of 568pc. The star is a visual apparent binary with a second roughly equal brightness star about two arcseconds away. In our images the two objects merge in all but very few cases. The second star is in the background at about 672pc

The light curve looks like a lot of noise. In each observing season the star just seems to vary randomly by about 2mag in V and 1.5mag in the I-Band. However, when one zooms in to a smaller part of the data (shown in the second figure), one can see that these variations are corelated and similar in all filters. The star hence varies by up to two magnitudes (a factor of about five in flux) as quickly as in one day. Note that due to the apparent companion being part of the measured light, the variations of GP Mon itself are actually even higher that the observed changes in magnitude.

Such large short term variations can either be caused by fast varying accretion rates or an extremely structured inner disk with lots of small and dense clumps of material. A detailed analysis of the colours and the variability is needed to verify either of those as the cause.