This week we look at the light curve of the variable star V718Per. It is situated in the IC348 target region and is a bona fide cluster member. It has been identified previously as an Orion Variable. This means that its brightness varies stochasticly. In the plot above we show the V, R, and I-band data of the object in our database as of last autumn.

We can see that the object shows long-term brightening and dimming behaviour. Indeed it appears that the object systematically brightens by about one magnitude and then fades back, over a period of about five years. In the last three years it has repeated this pattern again and is now on the cusp of the light curve. It will be interesting to see in the next few years if this is indeed a more or less periodic pattern. If this is indeed the case, then this could be caused by some large-scale pattern in the orbiting disk material. Given the five year period, this would be something that is accessible to resolve with interferometers like ALMA, because it would have a separation from the star of about three astronomical units.

Our analysis of the light curve shows that the source is classified as a dipper. Furthermore, the changes in colour during the dimming events suggest that the material occulting the star is made up of dust grains that are on average much larger than what is usually found in the interstellar medium. It is hence feasible that an orbiting, dense disk structure, where dust grains can grow by sticking together due to collisions can explain the light curve. This could be caused e.g. by spiral patterns in the disk, which have been seen before at large scales, and should be present closer to the stars as well.

The light curve above also shows a few outlier data points, both below and above the usual brightness. While some of these could potentially be attributed to photometry errors, source mis-identification etc., some of them seem to be real. In particular the deep, ~1mag dimming event at time MJD=59600 occurs in both the V and R filters. So this is likely a short dimming event by material very close to the star. Similarly, some of the short brightening events occur in more than one filter at the same time. They could hence by short accretion bursts. It is hence very difficult without a detailed analysis to decide if individual, ‘outlier’ data points are real or actual errors.