We stick with the winter targets for this week and look at the long term light curve of the object AH Ori. This is a know young variable star of Orion type in the Orion Nebula (M42).

This is one of our most observed fields. Thus, the light curve for the object contains in access of 12000 data points. The majority of which is in the B, V, and I filters, but in the last two years, we have also excellent coverage in R. There are of course additional data in Halpha and the odd U-band observation.

In the plot we show our long term (9 years) data in BVRI. For clarity the magnitudes are shifted as indicated in the legend for better visibility. The most notable aspect of the data is that the short term variation (which looks like noise, but is real) amounts to about 1.5-2.0 magnitudes. The larger values occur in the shorter wavelength filters. Additionally there are longer term slow up and down trends of up to one magnitude for the baseline average brightness.

It is worth zooming into the data and look at the details. There are many short term dimming events, which are the cause for the ‘noise’ in the long term plot. One interesting ‘feature’ in the data seems to be the relative calmness of the object during the 2014/15 observing season. There, much less variability is evident compared to the other years. One of the HOYS projects we are planning is to identify stars that change their behaviour over time. This object would probably be one that gets flagged up for detailed analysis in such an investigation.