HOYS stands for “Hunting Outbursting Young Stars” – and this week we actually show one 🙂
The above image is the R and I-band light curve of the young star V557Mon. It is usually a very faint star near the edge of the Rosette Nebula. During the winter observing period of 2024-25 the object underwent a strong outburst of about 4mag in amplitude. The outburst lasted nicely for the entire visibility period and the source was in its faint state the season before and after. You can read some more details in this paper (we were not involved in that one), where you can see this was a so-called EXor type outburst.
From the light curve you can see that during the normal behaviour we barely observe the star. Photometry is only available from the very few deepest images as the star is usually about 19.5mag in the R-Band. Indeed we only have a few reliable data points in R, I, and some very deep U-band images during the faint state. But in the outburst it was reliably detected in all filters due to the brightness increase.