When you do a survey (like HOYS), one of the things you tend to find are things you did not expect. Well, here is one. One of our students stumbled across the above light curve. For obvious reasons we won’t tell you which object it is 😉.

As you can see, it looks quite interesting. Indeed it looks like (and actually is) an interference pattern of two frequencies which are very close together. Such interference produces beats with a frequency that is equal to the frequency differences of the two signals. Check out Wikipedia for more details.

A bit of analysis shows that we have two periodic signals in the data. Both of them have periods very close to two days. One period is slightly shorter than two days and one slightly larger. Our usual observing cadence is one day. This is why the pattern shows up so clearly. When both signals are in phase, i.e. their maxima occur at the same time, then we see very large changes from day to day. But because the frequencies of the two signals are slightly different, over time they get out of phase, to the point where they cancel each other out (one object is bright when the other is faint and vice versa). Then we see no change from day to day. These are the knots in the beats you can see. These occur in the light curve roughly every 25 days. This means that the period difference between the two signals is approximately 3.5hr.

We have some ideas what the object could be, but need to have a look at a lot more data and maybe take some additional observations, including spectra to verify these. A quick check has not revealed anything else similar in the data, i.e. this is not a very common phenomena. We will keep you updated what this mystery object could be. Before you get your hopes up: The last time we found a mystery object it took more than 5yr to figure it out and get the paper written and published. Thus, please don’t expect a full update next week ☺