Spots on young stars again this week 🙂

There have been plenty of posts about this – so please drawl the archive of posts. We have so far determined the rotation period of the stars using the periodic variability. In addition we measured the amplitudes of the variation in brightness in the different filters to determine the size and temperature of the spot, relative to the star. Again, there multiple posts and also papers about this already.

However, there is a lot more information in the shape of the phase folded light curves – not just the amplitudes. We have now started to look into using the shape of the light curves to not just determine the size and temperature of the spot, but also its location (latitude) on the surface as well as the inclination of the stellar rotation axis. In the animation above you can see how the phase folded light curve of a spot at a latitude of 50 degrees would look like, if the inclination of the stellar rotation axis is 60 degrees and the radius of the spot is 15 degrees.

The light curve looks flat at maximum brightness when the spot is not visible. It then dims to a minimum while the spot rotates into the meridian of the projected stellar surface. If the spot was at a lower latitude, the flat bright part of he phase folded light curve would be longer. Similarly, a higher inclination would cause a similar change. In the second plot we show an example light curve of one of the stars we identified before as having aa cold spot and rotating with a period of about 3.5 days. We can see that the general shape of the light curve looks similar.

However, in the example the flat bright part of the light curve is about half the rotation period. This indicates that the spot is most likely at a lower latitude. Also the decree in brightness is almost 15 percent, so the spot is probably larger than the one in the example simulation. The student now has to find a way to identify which of the many possible model light curves fits best to the observations and how accurately each of the parameters can be determined. Lets see how that goes 🙂