For this weeks light curve we stay in the field of Sigma Ori. Indeed this area on the sky contains a large number of variable young stars which are part of the Sigma Ori cluster.

Following our call to image this region to support HST observations, one participant has uploaded his monitoring data of the field from the last 2.5 months. We show the B, V, R, and I light curve of the star BG Ori in the above figure. It is right in the cluster of young stars and it does show some excess infra-red emission, indicating a disk.

The light curve shows repeated brightening and fading events which occur in all filters. The amplitude of the variations is much brighter at shorter wavelength. Without a detailed analysis of the colours, it is not possible to be sure if the variations are due to changes of the amount of disk material along the line of sight or a change in the mass accretion rate.

The time scales of the the variations can be extremely small. Some half magnitude dimming events are as short as a single night. In the long term, over the six years we do have data, the star behaves in the same way. A lot of variability, but always within the bounds observed in the light curve for the last couple of months.