We have a look at some items related to spots on young stars this week. The properties (size and temperature) of these spots are determined from amplitudes in periodic light curves in various filters. This requires to first find the periodic light curves, i.e. to determine the (rotation) period of the star. Once we have the spot properties, we can ask questions such as: Do large star spots occur more likely on objects with shorter or longer rotation periods? The size of the spots certainly has something to do with the magnetic fields of the star, and that in turn will depend to some extend on the rotation period, as well as the internal structure of the star.
However, simply plotting the number of ‘large’ spots against the period is not enough. The reason is that finding periodic signals in our data does depend on the amplitude (spot size) and the period of the star. Thus, if one wants to analyse such simple questions as the one above, we need to know the bias/selection effects in our sample. Hence, we need to simulate how probable it is to find a periodic signal of a given period and amplitude. In the above plot this is shown for a half year bit of data for one star which is reasonably bright.
One can see that signals with very small amplitudes are very unlikely to be found for any period. Large amplitude signals are always found. However, for in-between amplitudes, one can see that the probability of finding the period depends on the period itself. In the example shown, periods of about 2 weeks are much less likely to be detected than 1 week ones.
This is of course just one example for one 6 months part of a single light curve. We need to evaluate this for the entire sample of stars to be able to answer the above question. This will take while, but we’ll make another post when the simulations are finished 🙂