While our server is off-line (nothing is broken, so hopefully this will not be for too long), we show a few variables that have come up during our ongoing analysis.
One of the students is working on ensuring that all light curves only contain 100% reliable data points to create a large, unbiased sample of variables. This will be used to study the statistical behaviour of the variations and to learn about the small scale disk structure that surrounds these objects. One of the fun things one can do is to make a list of the ‘most variable’ sources based on different criteria.
The above mosaic is one such selection, based on the “Stetson-Welch” index, and showing the 9 most variable objects. If you are interested, table 1 in this paper, shows you how you can calculate it and other variability indices. One of the interesting things is that each ‘variability index’ does measure something different in the light curves. Thus, ‘most variable’ means something different depending on what index one uses.
In any case, in the mosaic above you can see that there are very different behaviours visible in the light curves selected. There are long term trends, as well as light curves that seem to just look like noise (esp. bottom left and top right). But if one “zooms in”, it becomes clear that these sources do indeed vary in all filters in a similar way on very short timescales, creating the impression of ‘noise’.
The object in the middle top panel, is V2492Cyg. This has featured many times before (week 91, week 140, week 175), and always shows up near the top of any lists looking for most unusual objects. Lately (for now almost 700 days) the object is totally invisible to all our telescopes. I checked our last I-Band image, and while it has a limiting magnitude of about 18mag, there is not even the slightest hint of an object being detected at the coordinates of the source. This means it is now at least 600 times fainter than what it was during the peak brightness in 2016. We will keep observing to see if/when it returns to being visible.