This week we look at some of the progress with the next HOYS paper. We showed a preliminary plot of how periodic and symmetric our light curves are in a previous post. This has now been updated and cleaned up. It now only contains stars which are potential members of young HOYS clusters that are less than 3000 light years away. Furthermore, it includes only stars that are clearly variable. This has naturally reduced the number of stars in the plot, but it is now a much more simple to analyse sample.
In the plot the x-axis (Q Index) shows how periodic the light curve is. Strictly periodic objects (e.g. eclipsing binaries) would have Q=0. In stars where the variation in brightness is completely random, i.e. stochastic, the Q-index is equal to one. From Q=0 to Q=1 the behaviour of the sources slowly turns more and more stochastic. The position on the y-axis (M Index), shows how asymmetric the light curve of the star is. Objects that are dominated by dimming events, e.g. here, have larger positive M-values in excess of +0.5. The opposite behaviour, i.e. light curves that show brightness eruptions, e.g. here, do have larger negative M-values below -0.5. More symmetric light curves, that can for example look like a sine-function, e.g. here, are found in-between the two extremes, near M=0. The symbol size in the plot is proportional to the amount of variability (called the Stetson Index), i.e. stars with larger amplitudes are represented by larger symbols.
Here is the draft text for the description of the figure from the paper: “The most common variability type of the light curves is symmetric, around M=0. There is a more or less homogeneous distribution of Q values in the range from 0.0 to 0.7. A much larger fraction of sources has higher Q-values. Typically, sources with larger StetsonJ indices (the amount of variability) have more asymmetric light curves. Note that a fraction of 1-3 percent of all variable objects lies outside the nominal values for Q, i.e. they are outside the 0.0 to 1.0 range. The reason for these are the range of different uncertainties of the photometric data points in each light curve and the need to use some average of it for the determination of Q.” More soon ….