In week 110 (more than 4 years ago) we had a look at the star BL Vel, which is situated in the southern HOYS field of Gaia19eyy. Back then we found that on occasion the star shows periodic variability with a period of almost exactly 9 days. However, the amplitude was quite variable. It could be about 0.2mag, but the periodic signal would also disappear for times.
We hence decided to have another look at the data. In the picture above we show the V and R-band data from 2022/23. We can see that for the first ~50 days shown, the nine day periodic signal is clearly visible. The amplitude in each cycle seems to be increasing. After that however, the clear signal almost disappears and one needs to look very carefully to at least occasionally spot the variations.
During the entire next year there are only very low amplitude variations, but the periodicity is seen. Lately, over the last few months the higher amplitude signal has re-appeared and currently the amplitudes are again 0.2mag. All the while, the shape of the variations changes. Sometimes it looks almost sinusoidal, at other times short (~2d) steep increase are followed longer (7d) steady declines. Occasionally this even flips around with longer increases and fast declines.
So the source is clearly periodic which leaves only surface spots or orbiting disk material as the cause for the variability. A more detailed investigation is need to find out what is going …. anyone? 🙂